DESCRIPTION
The A6214 is a single-IC switching regulator that provides
constant-current output to drive high-power LEDs. It integrates
a high-side N-channel DMOS switch for DC-to-DC step- down
(buck) conversion. A true average current is output using a
cycle-by-cycle, controlled on-time method.
Output current is user-selectable by an external current sense
resistor. Output voltage is automatically adjusted to drive
various numbers of LEDs in a single string. This ensures the
optimal system efficiency.
LED dimming is accomplished by a direct logic input
pulse-width-modulation (PWM) signal at the Enable pin.
Alternatively, an Analog Dimming input can be used to calibrate
the LED current, or implement thermal foldback in conjunction
with external NTC thermistor.
The A6216 has the added capability to generate its own PWM
dimming frequency and duty cycle in stand-alone mode.
The A6214 is provided in a compact 10-pin narrow SOIC
package (suffix LK). The A6216 is in 16-pin TSSOP (suffix
LP), both with exposed pad for enhanced thermal dissipation.
It is lead (Pb) free, with 100% matte-tin leadframe plating.
A6214-16-DS, Rev. 4
FEATURES AND BENEFITS
• AEC-Q100 qualified
• Supply voltage 4.5 to 55 V
• 2 A maximum output over operating temperature range
• Integrated MOSFET switch
• Able to use either Schottky or silicon low-side diode
• True average output current control
• Internal control loop compensation
• Integrated 5 V, 10 mA regulator for driving external load
• PWM dimming via direct logic input down to 0.1% at 200 Hz
• Standalone internal PWM dimming (A6216)
• Analog dimming for brightness calibration and thermal
foldback
• Low-power shutdown (1 µA typical)
• Fault flag output (A6216)
• LED string open and short protection
• Cycle-by-cycle current limit
• Undervoltage lockout (UVLO) and thermal shutdown (TSD)
• Robust protection against:
□Adjacent pin-to-pin short
□Pin-to-GND short
□Component open/short faults
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
PACKAGES:
Not to scale
A6214 and A6216
Figure 1: A6214 (LK Package) Typical Application Circuit
APPLICATIONS:
Automotive lighting
• Daytime running lights
• Front and rear fog lights
• Turn/stop lights
• Map light
• Dimmable interior lights
January 21, 2013
A6214: 10-Pin SOICN (suffix LK)
A6216: 16-Pin eTSSOP (suffix LP)
Not to scale
LED+
GND
V
IN
(4.5 to 55 V)
EN/PWM
C
BOOT
R
ON
L1
C2
R
SENSE
GND
D1
1
2
3
4
5
10
9
8
7
6
SW
BOOT
GND
CSH
CSL
VIN
TON
EN
ADIM
VCC
A6214
ADIM
External PWM
dimming signal
External analog
dimming signal
C
IN
C
LED
November 1, 2016
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
2
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
SELECTION GUIDE
Part Number Internal PWM and
FAULT Flag Package Packing
A6214KLKTR-T No 10-pin SOICN with exposed thermal pad 3000 pieces per 13-in reel
A6216KLPTR-T Yes 16-pin TSSOP with exposed thermal pad 4000 pieces per 13-in reel
Table of Contents
Features and Benefits 1
Description 1
Applications 1
Packages 1
Typical Application Circuit (A6214) 1
Typical Application Circuit (A6216) 2
Selection Guide 2
Specifications 3
Absolute Maximum Ratings 3
Thermal Characteristics 3
Pinout Diagrams and Terminal List Tables 4
Functional Block Diagrams 5
Electrical Characteristics 7
Characteristic Performance 9
Functional Description 11
Application Circuit Diagrams 18
System Failure Detection and Protection 21
Package Outline Drawings 23
Figure 2: A6216 (LP Package) Typical Application Circuit
LED+
GND
V
IN
(4.5 to 55 V)
C
IN
EN/PWM
L1
GND
D1
ADIM
R1*
* R1, R2, R3 used in stand-alone
mode for internal PWM dimming
V
CC
VCC
FAULT
External PWM
dimming signal
External analog
dimming signal
3
4
6
7
5
RANGE
BOOT
GND
CSH
CSL
FULL
TON
EN/PWM
ADIM
VCC
A6216
1
2
8
DR
GND FPWM
14
13
11
10
12
16
15
9
FAULT
SW
VIN
FULL
FULL = “HIGH” = 100% Duty Cycle
FULL = “LOW” = DR controls Duty Cycle
RANGE
RANGE = “HIGH” = 0 to 100% Duty Cycle
RANGE = “LOW” = 0 to 30% Duty Cycle
R
ON
C
BIAS
R2* R3*
C
BOOT
C
LED
R
SENSE
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
3
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ABSOLUTE MAXIMUM RATINGS
Characteristic Symbol Notes Rating Unit
Supply Voltage VIN –0.3 to 60 V
Bootstrap Drive Voltage VBOOT –0.3 to VIN + 8 V
Switching Voltage VSW
Continuous –1.5 to VIN + 0.3 V
Pulsed, t < 20 ns –0.3 to VIN + 3 V
Enable and TON Voltage VEN , VTON –0.3 to VIN + 0.3 V
Linear Regulator Terminal VCC –0.3 to 7 V
ADIM Pin Voltage VADIM –0.3 to 7 V
Current Sense Voltages VCSH, VCSL –0.3 to VIN + 0.3 V
FAULT, FULL, RANGE, and
FPWM Voltages
VFAULT, VFULL,
VRANGE, VFPWM
A6216 only –0.3 to 7 V
DR Pin Voltage VDR
A6216 only; DR pin voltage must not be higher
than VCC even when device is off (VCC = 0 V) –0.3 to VCC + 0.3 V
Operating Ambient Temperature TAK temperature range for automotive –40 to 125 °C
Maximum Junction Temperature TJ(max) 150 °C
Storage Temperature Tstg –55 to 150 °C
THERMAL CHARACTERISTICS*: May require derating at maximum conditions; see application section for optimization
Characteristic Symbol Test Conditions* Value Unit
Package Thermal Resistance
(Junction to Ambient) RθJA
A6214 Package LK On 4-layer PCB based on JEDEC standard 35 °C/W
A6216 Package LP
On 4-layer PCB based on JEDEC standard 34 °C/W
On 2-layer PCB with 3.8 in.2 of copper area each side 43 °C/W
Package Thermal Resistance
(Junction to Pad) RθJP 2 °C/W
*Additional thermal information available on the Allegro™ website.
SPECIFICATIONS
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
4
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Pinout Diagram for A6214
(LK Package)
Terminal List Table for A6214 (LK Package)
Number Name Function
1 VIN Supply voltage input voltage for IC and buck regulator
2TON Regulator on-time setting resistor terminal. Connect a resistor
between VIN and TON to set the switching frequency.
3 EN/PWM Logic input for Enable and PWM dimming
4 ADIM Analog dimming control voltage input
5 VCC Internal IC bias regulator output. Connect 1uF MLCC to GND.
Can be used to supply up to 10mA for external load.
6 GND Ground terminal
7 CSL Current Sense (Lower end) feedback input for LED current
8 CSH Current Sense (Higher end) feedback input for LED current
9 BOOT DMOS gate driver bootstrap terminal
10 SW Switched output terminal
-PAD Exposed pad for enhanced thermal dissipation; connect to GND
Pinout Diagram for A6216
(LP Package)
VIN
TON
EN
ADIM
VCC
SW
BOOT
CSH
CSL
GND
PAD
1
2
3
4
5
10
9
8
7
6
VIN
TON
EN/PWM
ADIM
VCC
DR
GND
FULL
SW
BOOT
CSH
CSL
GND
FAULT
FPWM
RANGE
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PAD
Terminal List Table for A6216 (LP Package)
Number Name Function
1 VIN Supply voltage input voltage for IC and buck regulator
2TON Regulator on-time setting resistor terminal. Connect a resistor
between VIN and TON to set the switching frequency
3 EN/PWM Logic input for Enable and PWM dimming
4 ADIM Analog dimming control voltage input
5 VCC Internal IC bias regulator output. Connect 1uF MLCC to GND.
Can be used to supply up to 10mA for external load
6 DR Dimming Ratio control. In stand-alone mode: connect to resistor
divider network from VCC to set the dimming PWM duty cycle
7 GND Ground terminal
8 FULL Selects 100% dimming duty cycle or DR control of duty cycle
9 RANGE Selects DR control range, high range gives DR control from 5%
to 100%, low range gives DR control from 5% to 33%.
10 FPWM Dimming PWM frequency control. In stand-alone mode, connect
a resistor to GND to set the dimming PWM frequency
11 FAULT Open-drain output which is pulled low in case of fault. Connect
through an external pull-up resistor to the desired logic level.
12 GND Ground terminal
13 CSL Current Sense (Lower end) feedback input for LED current
14 CSH Current Sense (Higher end) feedback input for LED current
15 BOOT DMOS gate driver bootstrap terminal
16 SW Switched output terminal
-PAD Exposed pad for enhanced thermal dissipation; connect to GND
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
5
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
FUNCTIONAL BLOCK DIAGRAMS
Figure 3: Simplied Functional Block Diagram for A6214
LED+
GND
L1
GND
D1
SW
BOOT
GND
CSH
CSL
V
IN
VCC
On-Time
Select
Duty
Cycle
Control
LDO
Enable
Internal 5 V
i
LED
Reference
ADIM
ADIM
R
adj
is optional. It can be used to fine-adjust the LED current
in case the desired value of R
SENSE
is not available.
A6214
V
IN
(4.5 to 55 V)
R
adj C
LED
RSENSE
R
ON
C
IN
EN/PWM
VOUT VCC
VIN
TON
EN/PWM
VIN
On-Time
CBIAS
VREF
C
BOOT
VOUT
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
6
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 4: Simplied Functional Block Diagram for A6216
LED+
GND
L1
GND
D1
SW
BOOT
GND
CSH
CSL
TON
VCC
VIN
LDO
ADIM
ADIM
FAULT
Mode
FAULT
FAULT
OSC
FPWM
DR
R1
R2
Enable
R
FPWM
Up to 10 mA
external load
RANGE
FULL
A6216
VCC
V
IN
(4.5 to 55 V)
C
IN
R
ON
On-Time
Select
VOUT
CBIAS
Internal
5 V bias
VIN
EN/PWM
EN/PWM
VCC
Internal PWM
Duty Cycle
Generator
(200 Hz to 1 kHz)
VREF
(0 to 200 mV)
i
LED
Reference
Buck
Converter
Duty Cycle
Control
On-Time
LED
Current
Differential
Amp
Gate
Driver
V
IN
C
BOOT
VCC
RSENSE
R
adj
C
LED
VOUT
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
7
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ELECTRICAL CHARACTERISTICS: Valid at VIN = 12 V, VOUT = 6 V, TA = –40°C to 125°C, typical values at TA = 25°C, unless
otherwise noted
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
Input Supply Voltage VIN 4.5 – 55 V
VIN Undervoltage Lockout Threshold VUVLO VIN increasing – – 4.3 V
VIN Undervoltage Lockout Hysteresis VUVLO
_
HYS VIN decreasing – 150 300 mV
VIN Pin Supply Current IIN VCSH – VCSL = 0.5 V, EN = VIH, RON = 402 kΩ – 5 – mA
VIN Pin Shutdown Current IINSD EN = VIL – 1 10 µA
Buck Switch Current Limit Threshold ISWLIM 2.5 3.25 4 A
Buck Switch On-Resistance RDS(on) VBOOT = VIN + 4.3 V, TA = 25°C, ISW = 0.5 A – 0.25 0.4 Ω
BOOT Undervoltage Lockout
Threshold VBOOTUV VBOOT to VSW increasing 3.1 3.4 3.7 V
BOOT Undervoltage Lockout
Hysteresis VBOTUVHYS VBOOT to VSW decreasing – 750 – mV
Switching Minimum Off-Time tOFFmin VCSH – VCSL = 0 V – 75 100 ns
Switching Minimum On-Time tONmin VCSH – VCSL = 0.3 V – 75 100 ns
Selected On-Time tON RON = 402 kΩ 800 1000 1200 ns
REGULATION COMPARATOR AND ERROR AMPLIFIER
Load Current Sense Regulation
Threshold at 100%
1VCSREG
VCSH – VCSL decreasing, SW turns on, ADIM
tied to VCC 194 200 206 mV
Output Current Sense Common
Mode Voltage (measured at CSL pin) VOUT VIN = 55 V, fSW = 500 kHz, iLED = 0.5 A 2.65 – 50 V
CSH Input Sense Current ICSH VCSH – VCSL = 0.2 V – –190 – µA
CSL Input Sense Current ICSL VCSH – VCSL = 0.2 V 50 75 100 µA
INTERNAL LINEAR REGULATOR
VCC Regulated Output VCC 0 mA < ICC < 5 mA, VIN > 6 V 4.85 5 5.15 V
VCC Current Limit
2iVCCLIM VCC ≥ 4.75 V 10 20 – mA
VCC Dropout Voltage VLDO Measure VIN – VCC. VIN = 5 V, iVCC = 9 mA – 0.15 0.35 V
ENABLE/PWM INPUT
Logic High Voltage VIH VEN increasing 1.8 – – V
Logic Low Voltage VIL VEN decreasing – – 0.4 V
EN Pin Pull-down Resistance RENPD VEN = 5 V – 100 – kΩ
Maximum PWM Dimming Off-Time tPWML
Measured while EN = low, during dimming
control, and internal references are powered-on
(exceeding tPWML results in shutdown)
10 17 – ms
INTERNAL PWM DIMMING (A6216 ONLY)
Internal PWM Dimming Frequency fPWM External RFPWM = 30 kΩ from FPWM pin to GND 180 200 220 Hz
FULL, RANGE Pins Input Low Voltage VIL – – 0.8 V
FULL, RANGE Pins Input High Voltage VIH 2 – – V
Internal PWM Duty Cycle
DPWM5(L)
VDR driven by resistor divider from VCC,
VCC / VDR = 9.72, fPWM = 200 Hz, RANGE = low 4.75 5 5.25 %
DPWM5(H)
VDR driven by resistor divider from VCC,
VCC / VDR = 29.2, fPWM = 200 Hz, RANGE = high 4.5 5 5.5 %
DPWM90(H)
VDR driven by resistor divider from VCC,
VCC / VDR = 1.62, fPWM = 200 Hz, RANGE = high 87 90 93 %
Continued on the next page…
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
8
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
ANALOG DIMMING INPUT
Input Voltage for 100% LED Current VADIMH VCSH – VCSL = VCSREG 2.1 – – V
Regulation Threshold at 50% Analog
Dimming VCSREG50 VADIM = 1 V – 100 – mV
Regulaton Threshold at 20% Analog
Dimming VCSREG20 VADIM = 0.4 V 38.4 40 41.4 mV
FAULT PIN (A6216 ONLY)
FAULT Pull-Down Voltage VFAULT(PD) Fault condition asserted, pull-up current = 1 mA – – 0.4 V
FAULT Pin Leakage Current VFAULT(LKG) Fault condition cleared, pull-up to 5 V – – 1 µA
TIMERS
Cool Down Timer for Fault Retry tRETRY – 1 – ms
Delay Timer for Reporting LED Open
Fault tOPEN – 50 – µs
THERMAL SHUTDOWN
Thermal Shutdown Threshold
3TSD 150 165 180 °C
Thermal Shutdown Hysteresis TSDHYS – 25 – °C
1 In test mode, a ramp signal is applied across CSH and CSL pins to determine the CS regulation threshold voltage. In actual application, the average
CS voltage is regulated at VCSREG regardless of ripple voltage.
2 The internal linear regulator is capable of supplying up to 10 mA to external devices.
3 Determined by design and characterization. Not production tested.
ELECTRICAL CHARACTERISTICS (continued): Valid at VIN = 12 V, VOUT = 6 V, TA = –40°C to 125°C, typical values at
TA = 25°C, unless otherwise noted
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
9
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
CHARACTERISTIC PERFORMANCE
0
10
20
30
40
50
60
70
80
90
100
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4
Duty Cycle (%)
VDR (V)
Internal PWM Duty Cycle vs DR Pin Voltage
(VIN = 12 V, VOUT = 6 V, RTON = 300 kΩ, fPWM = 300 Hz, TA = 25ºC)
Measured for RANGE=H
Target for RANGE=H
Measured for RANGE=L
Target for RANGE=L
0%
20%
40%
60%
80%
100%
0 0.4 0.8 1.2 1.6 2 2.4
Normalized LED Current (%)
ADIM Voltage (V)
Normalized LED Current vs ADIM Voltage
(VIN = 12 V, VOUT = 6 V, iLED = 1 A, TA = 25°C)
Measured Current
Target
Figure 5: Analog Dimming Performance –
LED current can be reduced linearly down to 10%
using the ADIM pin voltage.
Figure 6: PWM Dimming Performance –
Duty cycle down to ~0.1% (1000:1) can be achieved
with higher VIN or lower inductance.
Figure 7: Internal PWM Dimming Operation (A6216 only) –
Duty cycle is controlled by the voltage at DR pin.
Figure 8: Internal PWM Dimming Frequency
(A6216 only) as a function of FPWM Resistance
0.001
0.01
0.1
1
0.1 1 10 100
Normalize LED Current
PWM Duty Cycle (%)
Average LED Current vs. PWM Duty Cycle
(RTON = 442 kΩ, load = 2× LED at 1.5 A, fPWM = 200 Hz)
VIN = 24 V, L = 47 µH
VIN = 12 V, L = 22 µH
VIN = 12 V, L = 47 µH
Ideal
0
200
400
600
800
1000
1200
1400
1600
0 10 20 30
fPWM (Hz)
RFPWM (kΩ)
Frequency of Internal PWM vs. FPWM Resistance
(VIN = 12 V, VOUT = 6 V, VDR = 1.7 V, TA= 25°C)
Calculated
Measured
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
10
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
CHARACTERISTIC PERFORMANCE (continued)
Figure 9: Startup for PWM Dimming operation –
RTON = 442 kΩ, L = 22 µH, VIN = 12 V, Output = 2× LED at
1.5 A, PWM = 1 kHz 50%. Note that there is a ~150 µs delay
for the rst PWM = H pulse, but none for subsequent pulses.
Figure 10: PWM Dimming with on-time of just 10 µs –
RTON = 442 kΩ, L = 22 µH, VIN = 12 V, Output = 2× LED at
1 A. Note that the LED current takes ~5µs to ramp up to
its steady-state value.
CH1 = VPWM (5 V/div)
CH2 = VSW (5 V/div)
CH3 = VOUT (5 V/div)
CH4 = iLED (500 mA/div)
Time Scale= 500 µs/div
CH1 = VPWM (5 V/div)
CH2 = VSW (5 V/div)
CH3 = VOUT (5 V/div)
CH4 = iLED (500 mA/div)
Time Scale= 5 µs/div
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
11
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
The A6214 is a buck regulator designed for driving a high-current
LED string. It utilizes average current mode control to maintain
constant LED current and consistent brightness. The LED current
level is easily programmable by selection of an external sense
resistor, with a value determined as follows:
RSENSE = VCSREG / iLED
where VCSREG = VCSH – VCSL = 0.2 V typical.
If necessary, a resistor can be inserted in series with the CSL pin
to fine-tune the LED current, as shown below:
CSH
CSL Radj RSENSE
VCSREG
+
VSENSE
–
iLED
iCSH
iCSL
– +
iCSL × Radj
VCSREG = iLED × RSENSE + iCSL × Radj
Therefore
iLED = (VCSREG – iCSL × Radj) / RSENSE
Figure 11: How To Fine-Tune LED Current Using Radj
For example, with a desired LED current of 1.4 A, the required
RSENSE = 0.2 V / 1.4 A = 0.143 Ω. But the closest power resistor
available is 0.13 Ω. Therefore, the difference is
Radj × iCSL = 0.2 V – 1.4 A × 0.13 Ω = 0.018 V
where iCSL = 75 µA typical
Radj = 0.018 V / 75 µA = 240 Ω
The LED current is further modulated by the ADIM (Analog
Dimming) pin voltage. This feature can be used for LED bright-
ness calibration, or for thermal foldback protection. See Analog
Dimming section for details.
Switching Frequency
The A6214 operates in fixed on-time mode during switching. The
on-time (and hence switching frequency) is programmed using
an external resistor connected between the VIN and TON pins, as
given by the following equation:
tON = k × (RTON + RINT ) × ( VOUT / VIN )
fSW = 1 / [ k × (RTON + RINT )]
where k = 0.00434, with fSW in MHz, tON in µs, and RON and
RINT (internal resistance, 20 kΩ) in kΩ.
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
0 100 200 300 400 500 600 700 800 900 1000
fSW (kHz)
RTON (kΩ)
Figure 12: Switching Frequency vs. TON resistance
ENABLE AND DIMMING
The IC is activated when a logic high signal is applied to the EN
(enable) pin. The buck converter ramps up the LED current to a
target level set by RSENSE.
When the EN pin is forced from high to low, the buck converter
is turned off, but the IC remains in standby mode for up to 10 ms.
If EN goes high again within this period, the LED current is
turned on immediately. Active dimming of the LED is achieved
by sending a PWM (pulse-width modulation) signal to the EN
pin. The resulting LED brightness is proportional to the duty cycle
(tON
/ Period) of the PWM signal. A practical range for PWM dim-
ming frequency is between 100 Hz (Period = 10 ms) and 2 kHz.
If EN is low for more than 17 ms, the IC enters shutdown mode
to reduce power consumption. The next high signal on EN will
initialize a full startup sequence, which includes a startup delay
of approximately 150 µs. This startup delay is not present during
PWM operation.
The EN pin is high-voltage tolerant and can be directly connected
to a power supply. However, if EN is higher than the VIN voltage
at any time, a series resistor (1-10 kΩ) is required to limit the cur-
rent flowing into the EN pin. This series resistor is not necessary
if EN is driven from a logic input.
FUNCTIONAL DESCRIPTION
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
12
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
PWM DIMMING RATIO
The brightness of the LED string can be reduced by adjusting the
PWM duty cycle at the EN pin as follows:
Dimming ratio = PWM on-time / PWM period
For example, by selecting a PWM period of 5 ms (200 Hz PWM
frequency) and a PWM on-time of 5 µs, a dimming ratio of 0.1%
can be achieved. This is sometimes referred to as “1000:1 dim-
ming.”
In an actual application, the minimum dimming ratio is deter-
mined by various system parameters, including: VIN
, VOUT
,
inductance, LED current, switching frequency, and PWM
frequency. As a general guideline, the minimum PWM on-time
should be kept at 5 µs or longer. A shorter PWM on-time is
acceptable under more favorable operating conditions, such as
higher VIN and lower inductance.
INTERNAL PWM DIMMING (A6216 ONLY)
In addition to external PWM dimming through EN pin, the
A6216 is able to generate an internal PWM dimming signal in
stand-alone mode. Frequency of the internal PWM signal can be
set by connecting a resistor between FPWM pin and GND, as
given by the following equation:
fPWM = c / (RFPWM + RINT)
where c = 6400, with fPWM in Hz, and RFPWM and RINT (internal
resistance, 0.5 kΩ) in kΩ.
This frequency can be between 200 Hz and 1 kHz when RANGE
is High, or 200 Hz and 500 Hz when RANGE is Low. Duty cycle
of PWM signal is linearly proportion to the voltage at DR (Dim-
ming Ratio) pin. This is illustrated by the following chart:
DR pin
voltage (V)
3.43
90%
0%
Internal PWM
Duty Cycle
5%
0.17
100%
3.080 V
30%
RANGE = High
RANGE = Low
0.514 5~4
33%
Figure 13: Variation of PWM Duty Cycle
with respect to DR Pin Voltage
It should be noted that the internal PWM duty cycle depends on
the ratio between VCC and VDR. The voltages shown in the chart
are with VCC = 5 V. For better accuracy, derive the DR pin volt-
age using a resistor divider connected between VCC and GND.
A practical range of internal PWM duty cycle when RANGE =
High is between 5% (VDR = 0.17 V) and 90% (VDR = 3.08 V).
To improve accuracy at low duty cycles between 5% and 30%,
set RANGE to Low. If DR pin is above 3.4 V, duty cycle stays at
around 99% if RANGE = High, 33% if Low.
To disable internal PWM generation, tie DR pin to VCC pin. (Do
NOT leave DR pin floating or connected to GND.) The FPWM
pin can be either left open, or tied to VCC. Note that at any time
during stand-alone PWM dimming mode, if EN pin goes low, the
LED is turned off immediately. This is illustrated in figure below.
Internal PWM
External PWM
(EN pin)
LED Current
Figure 14: LED Current when Both Internal and Exter-
nal PWM Dimming Signals are Applied
ANALOG DIMMING
In addition to PWM dimming, the A6214/16 also provides an
analog dimming feature. When V
ADIM is over 2 V, the LED cur-
rent is at 100% level (as defined by the SENSE resistor). When
V
ADIM is below 2 V, the LED current decreases linearly down to
20% at V
ADIM = 0.4 V. This is shown in the following figure:
ADIM pin
voltage
2 V
200 mV
±6 mV
(100%)
0
0.4 V
40 mV
100 mV
1 V
VCSREG
Figure 15: ADIM Pin Voltage Controls SENSE Reference
Voltage (hence LED current)
It is possible to pull ADIM pin below 0.4 V to achieve lower
than 20% analog dimming. However, the linearity may suffer if
the LED ripple current become too large compared to the aver-
age current. For example, if the LED ripple current is ±100 mA,
then the average current can only be dimmed down to 100 mA
linearly.
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
13
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ADIM pin can be used in conjunction with PWM dimming to
provide wider LED dimming range over 1000:1. In addition, the
IC can provide thermal foldback protection by using an external
NTC (negative temperature coefficient) thermistor, as shown
below:
NTC
R1
R
P
R
S
VCC
ADIM
Figure 16: Using an External NTC Thermistor
to Implement Thermal Foldback
If analog dimming is not required, the ADIM pin must be con-
nected to VCC pin. (Do NOT leave ADIM pin floating or con-
nected to GND.)
OUTPUT VOLTAGE AND DUTY CYCLE
The figure below provides simplified equations for approximat-
ing output voltage. The output voltage of a buck converter is
approximately given as:
VOUT = VIN × D – VD × (1 – D ) ≈ VIN × D, if VD << V IN
D = tON / (tON + tOFF )
where D is the duty cycle, and VD is the forward drop of the
diode D1 (typically under 0.5 V for Schottky diode).
During SW on-time:
iRIPPLE = (VIN – VOUT) / L × tON = (VIN – VOUT) / L × t × D
where D = tON / t.
During SW off-time:
iRIPPLE = (VOUT + VD) / L × tOFF = (VOUT + VD) / L × t × (1 – D)
Simplified equation for output voltage:
VOUT = VIN × D – VD × (1 – D)
If VD << VIN, then VOUT = VIN × D approximately.
More precisely:
VOUT = (VIN – iAVG × RDS(on)) × D – VD × (1 – D) – iAVG × (DCR + RSC)
where DCR is ther internal resistance of inductor and RSC is the
sense resistance.
VIN
VOUT
SW
GND
MOS
CIN
L
D
iLRSC
VSW
iL
t
t
VIN
0
tON
Period, t
–VD
tOFF
iRIPPLE
Figure 17: Simplied Waveforms for a Buck Converter
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
14
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
MINIMUM AND MAXIMUM OUTPUT VOLTAGES
For a given input voltage, the maximum output voltage depends
on the switching frequency and minimum tOFF . For example, if
tOFF(min) = 150 ns and fSW = 2 MHz, then the maximum duty
cycle is 80%. So for a 12.5 V input, the maximum output is
approximately 10 V (based on the simplified equation of VOUT
= VIN × D). This means up to 3 LEDs can be operated in series,
assuming Vf = 3.2 V or less for each LED.
The minimum output voltage depends on minimum tON and
switching frequency. For example, if the minimum tON = 100 ns
and fSW = 1 MHz, then the minimum duty cycle is 10%. That
means with VIN = 24 V, the theoretical minimum VOUT is just
2.4 V. However, the internal current sense amplifier is designed
to operate down to VOUT = 2.65 V. Therefore the output voltage
should not go lower than 2.65 V, or else the current accuracy will
suffer.
To a lesser degree, the output voltage is also affected by other
factors such as LED current, on-resistance of the high-side
switch, DCR of the inductor, and forward drop of the low-side
diode.
As a general rule, switching at lower frequencies allows a wider
range of VOUT , and hence more flexible LED configurations.
0
2
4
6
8
10
12
14
16
18
20
22
24
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
VOUT (V)
Frequency (MHz)
VOUT(max) (V)
VOUT(min) (V)
Figure 18: Minimum and Maximum Output Voltage vs.
Switching Freqency
(VIN = 24 V, minimum tON and tOFF of 100 ns)
If the required output voltage is lower than that permitted by the
minimum tON , the controller will automatically extend the tOFF ,
in order to maintain the correct duty cycle. This means that the
switching frequency will drop lower when necessary, in order to
keep the LED current in regulation.
If the LED string is completely shorted (VOUT = 0 V), LED
current regulation will become impossible. The output current
will increase until it trips SW overcurrent protection. The IC
then shuts down and retries after approximately 1 ms cooldown
period.
THERMAL BUDGETING
The A6214 is capable of supplying a 2 A current through its
high-side switch. However, depending on the duty cycle, the
conduction loss in the high-side switch may cause the package to
overheat. Therefore care must be taken to ensure the total power
loss of package is within budget. For example, if the maximum
temperature rise allowed is ∆T = 50°C at the device case surface,
then the maximum power dissipation of the IC is 1.4 W. Assum-
ing the maximum RDS(on) = 0.4 Ω and a duty cycle of 85%, then
the maximum LED current is limited to 2 A approximately. At a
lower duty cycle, the LED current can be higher.
FAULT HANDLING
The A6214 is designed to handle the following faults:
• Pin-to-ground short
• Pin-to-neighboring pin short
• Pin open
• External component open or short
• Output short to GND
The waveform in the figure below illustrates how the A6214
responds in the case in which the current sense resistor or the
CSH and CSL pins are shorted together. Note that the SW pin
overcurrent protection is tripped at around 3.5 A, and the part
shuts down immediately. The part then goes through startup retry
after approximately 1 ms of cooldown period.
Figure 19: In case of sense resistor short fault –
Output current rises until it trips SW OCP at ~3.5 A. The
IC shuts off and retries after ~1 ms cooldown period.
CH1 = VPWM (5 V/div)
CH2 = VSW (5 V/div)
CH3 = VOUT (5 V/div)
CH4 = iLED (1 A/div)
Time Scale = 200 µs/div
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
15
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
As another example, the waveform in figure below shows the
fault case where external diode D1 is missing or open. As LED
current builds up, a larger-than-normal negative voltage is
developed at the SW node during off-time. This voltage trips the
missing detection function of the IC. The IC then shuts down
immediately, and waits for a cooldown period before retry.
Figure 20: In case of missing low-side diode –
SW voltage fall below –2 V and trips Missing-Diode
fault. FAULT pin (A6216 only) is pulled Low immediate-
ly. The IC shuts off and retries after cooldown period.
COMPONENT SELECTIONS
The inductor is often the most critical component in a buck con-
verter. Follow the procedure below to derive the correct param-
eters for the inductor:
1. Determine the saturation current of the inductor. This can be
done by simply adding 20% to the average LED current:
iSAT ≥ iLED × 1.2.
2. Determine the ripple current amplitude (peak-to-peak value). As
a general rule, ripple current should be kept between 10% and
30% of the average LED current:
0.1 < iRIPPLE(pk-pk) / iLED < 0.3.
3. Calculate the inductance based on the following equations:
L = (VIN – VOUT
) × D × t / iRIPPLE , and
D = (VOUT + VD
) / ( VIN + VD ) ,
where
D is the duty cycle,
t is the period 1/ fSW , and
VD is the forward voltage drop of the Schottky diode D1.
OUTPUT FILTER CAPACITOR
The A6214 is designed to operate in current regulation mode.
Therefore it does not require a large output capacitor to stabilize
the output voltage. This results in lower cost and smaller PCB
area. In fact, having a large output capacitor is not recommended.
In most applications, however, it is beneficial to add a small filter
capacitor (around 0.1 μF) across the LED string. This cap serves
as a filter to eliminate switching spikes seen by the LED string.
This is very important in reducing EMI noises, and may also help
in ESD testing.
ADDITIONAL NOTES ON RIPPLE CURRENT
• For consistent switching frequency, it is recommended to
choose the inductor and switching frequency to ensure the induc-
tor ripple current percentage is at least 10% over normal operat-
ing voltage range (ripple current is lowest at lowest VIN).
If ripple current is less than 10%, the switching frequency may
jitter due to insufficient ripple voltage across CSH and CSL pins.
However, the average LED current is still regulated.
• For best accuracy in LED current regulation, a low current
ripple of less than 20% is required.
• There is no hard limit on the highest ripple current percentage
allowed. A 40% ripple current is still acceptable, as long as both
the inductor and LEDs can handle the peak current (average cur-
rent × 1.2 in this case). However, higher ripple current % affects
the accuracy of LED current, and limits the minimum current that
can be regulated when using ADIM.
• In general, allowing a higher ripple current percentage enables
lower-inductance inductors to be used, which results in smaller
size and lower cost.
• If lower ripple current is required for the LED string, one solu-
tion is to add a small capacitor (such as 1 to 2.2 μF) across the
LED string from LED+ to GND. In this case, the inductor ripple
current remains high while the LED ripple current is greatly
reduced.
• The effectiveness of this filter capacitor depends on many fac-
tors, such as: switching frequency, inductors used, PCB layout,
LED voltage and current, and so forth.
• The addition of this capacitor introduces a longer delay in LED
current during PWM dimming operation. Therefore the accuracy
of average LED current is reduced at short PWM on-time.
CH1 = VFAULT (5 V/div)
CH2 = VSW (5 V/div)
CH3 = VOUT (5 V/div)
CH4 = iLED (1 A/div)
Time Scale = 1 µs/div
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
16
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
INDUCTOR SELECTION CHART
The chart in figure below summarizes the relationship between
LED current, switching frequency, and inductor value. Based on
this chart: assuming LED current = 1 A and L = 22 μH, then mini-
mum fSW = 0.7 MHz in order to keep the ripple current at 20% or
lower. (Note: VOUT = VIN / 2 is the worst case for ripple current).
If the switching frequency is lower, then a larger inductance must
be used to meet the same ripple current requirement.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 0.5 1 1.5 2
Switching Frequency (MHz)
LED Current (A)
L = 10
µH
L = 15
µH
L = 22
µH
L = 33
µH
L = 47
µH
Figure 21: Relation between minimum switching frequen-
cy and LED current, given different inductance used
(VIN = 12 V, VOUT = 6 V, ripple current = 20%)
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
17
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
VIN
GND
L1
D1
RSENSE
LED+
iRIPPLE
VIN
GND
L1
D1
RSENSE
LED+
iRIPPLE
iRIPPLE
Without output capacitor:
The same inductor ripple current flows through
sense resistor and LED string.
With a small capacitor across LED string:
Ripple current through LED string is reducted, while
ripple voltage across RSENSE remains high.
Figure 22: Using an Output Filter Capacitor to Reduce
Ripple Current in LED String
Effects of Output Capacitor on LED Ripple Current
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
18
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
APPLICATION CIRCUIT DIAGRAMS
Figure 23: Application Circuit Example for A6214
(for driving 15 V LED at 1.3 A, fSW = 500 kHz)
LED+
GND
V
IN
(20 to 55 V)
EN/PWM
C4
0.1 µF
R1
442 kΩ
L1
47 µH 2 A
C5
1 µF
RSENSE
0.15 Ω
GND
D1
60 V
2 A
1
2
3
4
5
10
9
8
7
6
SW
BOOT
GND
CSH
CSL
VIN
TON
EN
ADIM
VCC
A6214
R
adj
71.5 Ω
C3
0.1 µF
100 V
C2
4.7 µF
100 V
C1
33 µF
63 V
LED
String
(~15 V)
i
LED
= (V
CSREG
– i
CSL
× R
adj
) / R
SENSE
= (0.2 – 0.000007 × 71.5) / 0.15 = 1.3 A
Suggested Components
Symbol Part Number Manufacturer
C1 HHXA630ARA330MHA0G United Chemi-Con
C2 C3225X7S2A475M200AB TDK
C3 CGA4J2X7R2A104M125AA TDK
L1 CDRH105RNP-470NC Sumida
D1 10MQ060NTRPBF Vishay
RSENSE RL1632R-R150-F Susumu
Figure 24: Application Circuit Example for A6216
(with External PWM and Thermal Foldback)
LED+
GND
V
IN
(4.5 to 55 V)
C
IN
EN/PWM
GND
V
CC
VCC
FAULT
External PWM
dimming signal 3
4
6
7
5
RANGE
BOOT
GND
CSH
CSL
FULL
TON
EN/PWM
ADIM
VCC
A6216
1
2
8
DR
GND FPWM
14
13
11
10
12
16
15
9
FAULT
SW
VIN
R
ON
442 kΩ
C
BIAS
1 µF
C
BOOT
0.1 µF
C
LED
0.1 µF
R
SENSE
0.2 Ω
10 kΩ
L1
47 µH 2 A
D1
60 V
2 A
i
LED
= 1 A
before foldback
VCC
R
S
R1
R
P
NTC
Thermal Foldback using NTC
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
19
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
APPLICATION CIRCUIT DIAGRAMS (continued)
Figure 25: Using two (or more) A6214/16 in parallel to drive the same LED string. Total
LED current is the sum of currents from each driver.
LED–
L1 RCS1
D1
SW
GND
CSH
CSL
CLED
VIN
LED+ L2
RCS2
D2
SW
GND
CSH
CSL
CLED
VIN
iLED1 iLED2
A6214/6 A6214/6
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
20
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
APPLICATION CIRCUIT DIAGRAMS (continued)
PROTECTION FROM OUTPUT LC-RESONANCE
During normal operation, if the LED load becomes disconnected
(due to a bad connector, for example), the output capacitor CLED
will be charged up to VOUT = VIN. Later, when the LED load is
reconnected, higher voltage stored in CLED will create a huge
current spike through the load. Normally this does not create
any problems, since the current spike will decay within a few
microseconds. However, if the LED load is connected through
long cables, the parasitic inductance LK in the cable will form an
LC-resonant circuit with CLED. If the resonant circuit is under-
damped, VOUT may oscillate and becomes negative. This could
subject CSH and CSL pins to negative spike voltage exceeding
their Absolute Maximum Ratings. Therefore the following pre-
cautions are recommended to avoid output oscillation:
• Use shortest possible LED cables to reduce LK.
• Use lower capacitance for CLED to reduce stored energy
(EC = 0.5 × CLED × VIN2).
• Critically damp the output LC-resonant circuit, as shown
in Figure 26. The drawback is additional power loss during
PWM dimming operation (since C1 is charged and discharged
through R1 during each PWM cycle).
In case the output LC resonance cannot be eliminated (due to
long LED cables, for example), consider adding a Schottky bar-
rier diode (SBD) in parallel with CLED, as shown in Figure 28.
The SBD clamps the negative spike of the LC resonance, so CSH
and CSL pins are protected. This is the most effective protection
with minimal side effects.
In underdamped circuit,
VOUT goes negative
In critically-damped circuit,
VOUT stays positive
C
LED
initially charged to
VOUT = 50 V when load is open
Time/µs
Figure 26: Countermeasure to Prevent VOUT Oscillation
During Output Intermittent Open/Short Fault
Figure 27: Simulation Results Showing Difference in VOUT
Between Underdamped and Critically-Damped Circuits
Figure 28: Using Schottky Diode to Clamp the Negative
spike from Output LC-Resonance
GND
L1
R
SENSE
CSL
C
LED
Add D2 to clamp the
negative voltage of
LC-resonant circuit
S1 LK
V
LED
CSH
D2
(60 V 1 A)
Total parasitic
inductance of cable
VOUT
V
LED
GND
L1
R
SENSE
C
LED
0.1 µF
ic = 50 V
R
OUT
1 Ω
CSH
CSL
Total resistance
of output path
L
K
0.4 µH
ic = 0 A
C1
0.22 µF
R1
1 Ω
ESR
10 mΩ
S1
V
OUT
Add R1 and C1 to
critically damp the
LC-resonant circuit
Large current spike
when S1 is closed
Total parasitic
inductance of cable
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
21
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
SYSTEM FAILURE DETECTION AND PROTECTION
LED+
GND
V
IN
EN/PWM
L1 = open
or short
R
SENSE
open or short
GND 1
2
3
4
5
10
9
8
7
6
SW
BOOT
GND
CSH
CSL
VIN
TON
EN
ADIM
VCC
A6214
D1 = open
or short
C4 open
or short
C1, C2 = open or short
R1 = open
or short
C5 = open
or short C3 open
or short
LED string open
or short to GND
Figure 29: Showing Various Possible Fault Cases in an
Application Circuit
IC-LEVEL FAILURE MODES
Protected against:
• Any pin open
• Any pin shorted to GND
• Adjacent pin-to-pin short
SYSTEM-LEVEL FAILURE MODES
Protected against open/short fault for all external
components, including:
• LED string
• Sense resistor
• Inductor
• Diode
• Input/output caps, etc.
Failure Mode Symptom Observed
FAULT flag
(A6216)
asserted?
A6214/16 Response
Inductor shorted Dim light from LED Yes Current spike trips SW secondary OCP and turns off switching. Retries after 1 ms.
Sense resistor open No light from LED Yes High differential sense voltage causes IC to shut off switching. Retries after 1 ms.
Sense resistor shorted Dim light from LED Yes Increases SW current, which eventually trips SW secondary OCP fault. Retries
after 1 ms.
Diode open Dim light from LED Yes Detects missing diode fault and shuts off switching. Retries after 1 ms.
Diode shorted No light from LED Yes Trips SW secondary OCP and turns off switching. Retries after 1 ms.
LED string open No light from LED Yes* Continue to switch at maximum tON (Since this fault cannot be distinguished from
VIN too low for LED forward drop)
LED string shorted to GND,
or Output cap shorted No light from LED Yes* IC unable to regulate LED current at VOUT = 0 V. SW current increases and trips
OCP. IC shuts down and retries after 1 ms.
LED string partially shorted Some LEDs are not on NO Normal operation (since IC has no way to know how many LED is supposed to
be in series).
Continued on the next page…
System Failure Mode Table (partial)
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
22
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Failure Mode Symptom Observed
FAULT flag
(A6216)
asserted?
A6214/16 Response
Output cap open Normal light from LED NO Normal operation (since IC only monitors inductor current).
Boot cap open Dim light from LED Yes* IC attempts to switch but can’t fully turn on SW. Short current spikes through
LED string.
Boot cap shorted No light from LED Yes* IC detects undervoltage fault across Boot cap and will not start switching.
TON resistor open Dim light from LED Yes SW turns on and hits secondary current limit, then shuts down. Retries after 1 ms.
TON resistor shorted Dim light from LED NO Operates at maximum switching frequency (minimum tON and tOFF). May hit
thermal limit.
Note (*)
• In case of LED current not in regulation, FAULT ag is asserted after approximately 50 µs timeout delay.
• For PWM dimming operation with on-time < 50 µs, FAULT ag is asserted if LED current fails to reach regulation after 16 PWM = H pulses.
• For PWM dimming operation with on-time > 50 µs, FAULT ag is only asserted when PWM = H. However, if the fault persists for 16 consecutive
PWM cycles, FAULT ag will be pulled Low and then it stays Low until the fault is cleared.
System Failure Mode Table (partial) (continued)
Figure 30: VIN too low for LED regulation. PWM = 500 Hz
2% (40 µs). FAULT = L after 16 PWM pulses.
Figure 31: VIN too low for LED regulation. PWM = 500 Hz
20% (400 µs). FAULT toggles each time PWM = H, but
stays Low after 16 PWM pulses.
CH1 = VPWM (5 V/div)
CH2 = VFAULT (5 V/div)
CH3 = VOUT (5 V/div)
CH4 = iLED (500 mA/div)
Time Scale = 5 ms/div
CH1 = VPWM (5 V/div)
CH2 = VFAULT (5 V/div)
CH3 = VOUT (5 V/div)
CH4 = iLED (500 mA/div)
Time Scale = 5 ms/div
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
23
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LK, 10-Pin SOICN with Exposed Thermal Pad
PACKAGE OUTLINE DRAWINGS
For Reference Only–Not for Tooling Use
NOT TO SCALE
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
A
0.40
0.30
0.25
0.19
8º
0º
0.685 ±0.20
C
SEATING
PLANE
SEATING PLANE
C0.10
10X
1.00 BSC
0.25 BSC
21
10
4.90+0.08
–0.10
3.91+0.08
–0.10
2.41 ±0.25 6.00 ±0.20
1.55 ±0.10
0.10 ±0.05
GAUGE PLANE
A
B
B
C
Exposed thermal pad (bottom surface)
5.60
1.000.55
1.75
2.41
3.30
10
21
C
Branded Face
3.30 ±0.25
PCB Layout Reference View
Terminal #1 mark area
Reference land pattern layout; all pads a minimum of 0.20 mm from all adjacent pads;
adjust as necessary to meet application process requirements and PCB layout tolerances;
when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can
improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
24
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LP, 16-Pin TSSOP with Exposed Thermal Pad
A
1.20 MAX
0.15
0.00
0.30
0.19
0.20
0.09
8º
0º
0.60 ±0.15
1.00 REF
C
SEATING
PLANE
C0.10
16X
0.65 BSC
0.25 BSC
21
16
5.00 ±0.10
4.40 ±0.10 6.40 ±0.20
GAUGE PLANE
SEATING PLANE
A
B
B
C
D
Exposed thermal pad (bottom surface); dimensions may vary with device
6.10
0.65
0.45
1.70
3.00
3.00
16
21
1
C
D
Branded Face
3 NOM
3 NOM
For Reference Only – Not for Tooling Use
(Reference MO-153 ABT)
Dimensions in millimeters. NOT TO SCALE
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
PCB Layout Reference View
Terminal #1 mark area
Reference land pattern layout (reference IPC7351 SOP65P640X110-17M);
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances; when
mounting on a multilayer PCB, thermal vias at the exposed thermal pad land
can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
Branding scale and appearance at supplier discretion
Standard Branding Reference View
YYWW
NNNNNNN
LLLL
= Device part number
= Supplier emblem
= Last two digits of year of manufacture
= Week of manufacture
= Characters 5-8 of lot number
N
Y
W
L
Automotive-Grade, Constant-Current 2 A
PWM Dimmable Buck Regulator LED Driver
A6214 and
A6216
25
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
For the latest version of this document, visit our website:
www.allegromicro.com
Revision History
Number Date Description
– September 23, 2015 Initial release
1 March 17, 2016 Added Load Current Sense Regulation Threshold footnote (page 7-8); updated Additional Notes on
Ripple Current (page 15).
2 April 6, 2016 Added Parallel Operation figure (page 19) and SBD Protection figure (page 20); updated Protection
from Output LC-Resonance (page 19); corrected LK package drawing dimension (page 23).
3 June 17, 2016 Updated k value (page 11).
4 November 1, 2016 Updated Functional Description (page 11); added Table of Contents.
Copyright ©2016, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of
Allegro’s product can reasonably be expected to cause bodily harm.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
