Order this document
by AN1319/D
MOTOROLA
SEMICONDUCTOR
APPLICATION NOTE
MOTOROLA INC., 1992 AN1319
Design Considerations for a Low Voltage
NĆChannel HĆBridge Motor Drive
Prepared by: Wayne Chavez
Discrete Applications Engineering
INTRODUCTION
In low voltage motor drives, it is common practice to use
complementary MOSFET half-bridges to simplify the gate
drive design. However, the P-channel FET within the
half-bridge usually has a higher on resistance or is larger
and more expensive than the N-channel FET. The alternative
solution is to design in an N-channel half-bridge. The
N-channel half-bridge uses silicon more efficiently, while
minimizing conduction losses and power device expense.
The tradeoff to take advantge of N-channel devices is found
in increased gate drive design complexity. Minimizing the
gate drive complexity in a brushed DC motor drive with an
all N-channel H-bridge is the focus of this note. In addition,
design considerations, diode snap and shoot-through current
are discussed and circuit solutions are given.
The result of the design is evaluation board DEVB151
shown in Figure 1. DEVB151 features an MPM3017
N-channel, H-bridge and circuitry designed to interface
power devices within the MPM3017 to microprocessor
outputs. The board drives 24-volt to 48-volt motors and can
handle 8 amps of continuous motor current. A detailed
description of the evaluation board is presented within this
Application Note.
AN1319
Figure 1. N-channel, H-bridge Motor Drive (DEVB151)
2
MOTOROLA AN1319
DESIGN CONSIDERATIONS
High-side Gate Drive Voltage
Using N-channel half-bridges requires circuitry that
produces voltage above the motor voltage rail and turns the
upper transistors on. One method of accomplishing this task
is to use a charge pump. The charge pump shown in Figure
2 provides a constant voltage greater than 12 volts above
the motor rail at all motor speeds, unlike the capacitor
bootstrap approach, and is less expensive than a transformer
isolated gate drive.
Figure 2. Charge Pump
10 kΩ
C10
.1µF
D11
1N5819
C9
1 µF
D10
+B
+B + Boost
U3
MC34151
C7
330 pF
Motor Supply
Voltage
1N5819
R28
10 kΩ
D10
+B
+B + Boost
1N5819
Ï
Ï
Î
Î
An oscillator, two capacitors and two diodes are all the
components necessary to build a charge pump. The inverter ,
MC34151, is configured as an oscillator with C7 and R28
determining the frequency. The charge pump action is as
follows. C10 charges up to the rail voltage minus a diode
drop when the IC’s output is low . When the IC’s output swings
high, C10 dumps charge into C9. The cycle is continuously
repeated. In steady state, the voltage across C9 is the
voltage swing of the IC’s output minus two diode drops. This
voltage is in series with the rail voltage, B+, and the sum
is sufficient to drive the high-side FETs.
Voltage losses in the charge pump are from the diode
forward drops and the IC’s output voltage swing. To minimize
the diode voltage drops, Schottky diodes are implemented.
The loss in the IC’s output voltage swing is dependent on
the level of current the charge pump is asked to support.
For example, if the charge pump is to support 50 mA, the
IC’s output swing diminishes by approximately 2 V. This is
of particular concern when operating from a voltage source
less than 15 V. Gate drive voltage is compromised when
operating from a supply voltage of less than 15 volts which
results in increased power dissipation.
High-side Gate Drive
Now that boost voltage is available for the high-side FETs,
a means of switching this voltage to the gate is needed.
Together the MDC1000A and a switched current source,
shown in Figure 3, accomplish this requirement.
The MDC1000A, a MOS turn-off device (MTO), is very
useful in the high-side FET applications. It discharges the
gate-to-source capacitance quickly and contains a zener
clamp for gate protection. To charge the gate-to-source
capacitance, the MTO passes current to the gate of the FET.
When the gate-to-source voltage reaches the zener clamp
voltage, the current is shunted through the zener. When the
current source is turned off, a resistor internal to the MTO
pulls down on the anode of the series diode. After the anode
voltage falls approximately one diode drop, the internal SCR
fires, discharging the gate-to-source capacitance. The series
gate resistor, R19, limits the rate of discharge of the gate
and therefore determines the turn-off time. It will be shown
Figure 3. High-side Gate Drive
33 Ω
U4
MDC1000A
Q1
R15 R16
+B
Q2
MPSA06
R10
+5V
U1
74HC00 +M
+B + Boost
10 Ω750 Ω
3.3 kΩ
MPSA56
R19
Motor Supply
Voltage
Positive Motor
Output
Î
ÏÏ
ÏÏ
ÏÏ
Ï
MOTOROLA
3
AN1319
Figure 4. Low-side Gate Drive
Motor Supply
Voltage
Positive Motor
Output
+B
+M
1N4148
D7 R21
1N4148
D8
R23
R22
MC34151
U2 240 Ω
33 Ω.01 Ω
later that this resistor also plays a key role in solving the
dynamic issues of the motor drive.
The current source used with the MTO consists of a PNP
transistor, Q1, and resistors R15 and R16. The FET turn-on
time is determined by the sourced current. The reference
current is the collector current of the level shifting transistor,
Q2, and is set by resistor R10. The reference current is
established when the NAND gate output is logic 0. The
reference current, though small, must be supported by the
charge pump.
Low-side Gate Drive
The low-side gate drive design, as shown in Figure 4, is
relatively simple compared to the high side. The MC34151,
used before as an oscillator in the charge pump, is an
integrated circuit specifically designed to drive the gate of
a power MOSFET. The input to this device can be a 5 volt
logic level signal like that of a microcontroller. The MC34151
is capable of sourcing and sinking approximately 1.5
amperes. Therefore, to limit the current into the gate and
control the turn-on time, a resistor, R22, is needed between
the IC and FET. An additional resistor, R23, in series with
Figure 5. Simplified Half-Bridge
Motor Supply
Voltage
Motor
_
+
Rgs
Rg
PWM
+B
Q1
Q2
a diode, D8, is placed in parallel with R22 to implement a
faster turn-off time. The need for separate turn-on and turn-off
times will become clear when the dynamic characteristics are
explained.
Dynamic Issues
In addition to static gate drive designs, more difficult
dynamic design challenges must be addressed. These
issues include diode snap and shoot-through current. A
description of these issues and solutions follows.
A pulse width modulated motor drive is usually a
continuous mode clamped inductive load – i.e. – current
continually flows through the inductance. Referring to the
simplified half-bridge circuit of Figure 5, current through the
motor ramps up when Q2 is on and freewheels through Q1’s
internal diode when Q2 is switched off.
When Q2 turns on again, the stored charge within Q1’s
diode must be cleared. The resulting drain current of Q2 is
shown in the turn-on waveform of Figure 6.
The first current peak in Figure 6 shows up as current
from the rail to ground, bypassing the motor . This current has
two components. The first is the expected reverse recovery
Figure 6. Turn-on Wave Form
Icont
ID
VDS
tb
ta
4
MOTOROLA AN1319
current of the internal diode of Q1. The second is dv/dt
generated shoot-through current.
Reverse recovery characteristics of the freewheeling
diode are at the root of the system design challenges.
Referring to Figure 6, FET intrinsic diode reverse recovery
tends to be fairly snappy; tb is much shorter than ta. It follows
that di/dt during tb is greater than during ta, and if
unmanageably high, invites unpredictable behavior and
unwanted voltage spikes. In addition, VDS falls very rapidly
during tb. Referring to Figure 5, the dv/dt created during tb
couples through to the gate-to-drain capacitance of the upper
FET. A current proportional to dv/dt and CDG flows through
the top FET gate impedance, develops a gate-to-source
voltage, and turns the FET on. The result is current from the
supply to ground through the half-bridge called shoot-through
current.
Shoot-through and reverse-recovery current bypass the
motor and therefore only contribute to power dissipation.
Other unwanted side effects consist of EMI and unpredictable
gate drive performance from high di/dts acting upon lead and
stray PCB trace inductance. However, control of diode snap
and shoot-through current is accomplished by employing a
gate drive impedance strategy.
The gate-to-source impedance of the upper FET as
shown in Figure 5, controls the voltage developed across
gate to source during tb and therefore controls the
shoot-through current. A low impedance will obviously
minimize shoot-through current, but there exists a value that
lets an optimal portion of shoot-through current pass. This
impedance can be adjusted until the turn-on waveform
appears to be critically damped. The FET is conducting as
the diode is snapping. If the total current is dominated by
the FET condition, the sharp snap of the diode is hidden.
The net effect is a softer recovery characteristic.
The turn-on gate impedance of the bottom pulse width
modulated FET of Figure 5 also plays a key role in softening
the reverse recovery characteristic. This impedance sets the
positive di/dt during ta. The stored charge in the freewheeling
diode is a function of applied di/dt and as ta becomes shorter ,
the diode snaps more severely. This implies that the turn-
on gate impedance must be set to a value that will create
a manageable positive di/dt and enable the strategy
undertaken to control diode snap.
An increase in power dissipation is sacrificed for a more
desirable turn-on waveform. Considering the problems that
arise with unmanageable di/dts, such as EMI, voltage spikes,
possible oscillation at turn-on, and possibly a large amount
of power dissipation, the trade-off is to the designer’s
advantage.
5.2”
PWR
MOTOROLA DISCRETE
APPLICATIONS
3.25”
R8
R9
D3
R10
D4
R11
R12
R13
R1
R2
R3
D1
R4
D2
R5
R6
R7
R14
R15
R16
R17
D6
D7
R28
D12
D13
C13
C14
Q4 Q2
Q3 Q1
R18
U4
C4
R22
D8
R23 R19
R20
U5
C5R21
R24
D9
R25
D10
D11
C9
C8
C7
C6
MPM3017 MOTOR DRIVE
DEVB151 REV A
+
C15
R27
R26
POWER I/O
+B
+M
–M
GND CON3
Q5
Q6
U6
C12
C10
U3
C11
C3
C2
M1
U1
D5
CON2
C1
J1
A BOT
A TOP
B TOP
B BOT
A CS
B CS
CS GND
GND
GND
U3
Figure 7. Component Layout
MOTOROLA
5
AN1319
R6
10 k
61
5
4
3
7
R28
330 pF
C9
MC34151
2
C12
.1
D12
19 V
C11
C10
D11
C1
D10
74HC00
.01 U1
+5 V
Q1
MPSA56 U4
MDC1000A
.01
C6
R16
R9
U3
1N5819
1N5819
1
2
3
1
+5 V
D4
R15
R10
R17
R12
U1
D3
R8
14
1 F
C2
R19
R14
.01
MPSA06
Q2
100 pF
C4
MPSA56
Q3
C7
C5
100 pF
R4
D6
U5
D8
R22
R23
1N4148
Q4
R21
R1
B BOT
B TOP
A BOT
A TOP
CON1 R7
1 F
C3
390
C15
R20
8
+
6
5
4
9
10
11
3
MPM3017
R18
A CS
CON2
GND
–M
+M
+B
CON3
+ B
GND
GND
CS GND
B CS
3
1
2
4.7 V
4.7 V
6
4
5
R11
2
3
1
3
1
23
2
3
1
3
1
2
4MPSA06
MDC1000A
2
1
23
1N4148
+5 V
4
9
2
1
2
1
4
5
3
2
1
4
32
1
1
2
3
31
8
11
MC34151
+5 V
R13
7
6
1N4148
D5
U2
.1
C8
GROUND
IN
1
C14
MC78L05
D13
OUT
U6
C13
17 V
R24
D7
1N4148
D9
R25
R26
TIP29B
MPSW06
Q5
R27
Q6
2
2
45
3
7
10
9
13
12
R3
D1
4.7 V
R5
R2
4.7 V
D2
U1
U1
6
1
1
Figure 8. MPM3017 Motor Drive Schematic
VDD
VDD VDD
µFµF
µF
µF
10
µF
33
µF
1 k
10 k
1 k
10 k
1 k
10 k
1 k
360
33
240
µFµF
1µF
4.8 k
4.8 k
1 k
1 k
.01
.01
33
33
240
750
3.3 k
10
3.3 k
750
µF
10 kΩ
Ω
Ω
ΩΩ
Ω
Ω
ΩΩ
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
µ
µ
6
MOTOROLA AN1319
Table 1. Parts List
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
Designators
ÁÁÁ
ÁÁÁ
Quantity
Description
ÁÁÁÁ
ÁÁÁÁ
Rating
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Manufacturer
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
Part Number
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
C1,C6,C7
ÁÁÁ
ÁÁÁ
3
.01 µF Ceramic Cap
ÁÁÁÁ
ÁÁÁÁ
100 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
C2,C3,C10,C11,C13,C14
ÁÁÁ
ÁÁÁ
6
1 µF Ceramic Cap
ÁÁÁÁ
ÁÁÁÁ
100 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
C4,C5
ÁÁÁ
ÁÁÁ
2
100 pF Ceramic Cap
ÁÁÁÁ
ÁÁÁÁ
100 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
C6,C8,C12
ÁÁÁ
2
.1 µF Ceramic Cap
ÁÁÁÁ
100 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
C9
ÁÁÁ
ÁÁÁ
1
330 pF Ceramic Cap
ÁÁÁÁ
ÁÁÁÁ
100 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
C15
ÁÁÁ
ÁÁÁ
1
390 µF Electrolytic Cap
ÁÁÁÁ
ÁÁÁÁ
100 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Sprague
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
80D391P100HA2
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
CON1,CON3
ÁÁÁ
ÁÁÁ
1
4 Terminal Connector
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
CON2
ÁÁÁ
ÁÁÁ
1
5 Terminal Connector
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
D1,D2,D3,D4
ÁÁÁ
ÁÁÁ
4
4.7 V Zener
ÁÁÁÁ
ÁÁÁÁ
500 mW
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
1N5230B
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
D5
ÁÁÁ
ÁÁÁ
1
LED (RED)
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
GI
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MV57124A
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
D6,D7,D8,D9
ÁÁÁ
ÁÁÁ
4
Diode
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
1N4148
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
D10,D11
ÁÁÁ
ÁÁÁ
2
Diode Schottky
ÁÁÁÁ
ÁÁÁÁ
1 A,40 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
1N5819
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
D12
ÁÁÁ
ÁÁÁ
1
19 V Zener
ÁÁÁÁ
ÁÁÁÁ
500 mW
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
1N5249B
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
D13
ÁÁÁ
ÁÁÁ
1
17 V Zener
ÁÁÁÁ
ÁÁÁÁ
500 mW
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
1N5247B
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
M1
ÁÁÁ
ÁÁÁ
1
N-ch H-Bridge
ÁÁÁÁ
ÁÁÁÁ
60 V/25 A
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MPM3017
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
Q1,Q3
ÁÁÁ
ÁÁÁ
2
PNP Transistor
ÁÁÁÁ
ÁÁÁÁ
80 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MPSA56
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
Q2,Q4
ÁÁÁ
ÁÁÁ
2
NPN Transistor
ÁÁÁÁ
ÁÁÁÁ
80 V
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MPSA06
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
Q5
ÁÁÁ
ÁÁÁ
1
NPN Transistor
ÁÁÁÁ
ÁÁÁÁ
80 V/2 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
TIP29B
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
Q6
ÁÁÁ
ÁÁÁ
1
NPN Transistor
ÁÁÁÁ
ÁÁÁÁ
80 V/1 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MPSW06
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R1,R3,R5,R7,R9,R11
ÁÁÁ
ÁÁÁ
6
1 kΩ Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R2,R6,R8,R12,R28
ÁÁÁ
ÁÁÁ
5
10 kΩ Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R4,R10
ÁÁÁ
ÁÁÁ
2
3.3 kΩ Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R13
ÁÁÁ
ÁÁÁ
1
360 Ω Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R14,R15
ÁÁÁ
ÁÁÁ
2
750 Ω Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R16,R17
ÁÁÁ
2
10 Ω Resistor
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R18,R21
ÁÁÁ
ÁÁÁ
2
.01 Ω Resistor
ÁÁÁÁ
ÁÁÁÁ
2.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Mills
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MRP-2-NI
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R19,R20,R23,R25
ÁÁÁ
ÁÁÁ
4
33 Ω Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R22,R24
ÁÁÁ
ÁÁÁ
2
240 Ω Resistor
ÁÁÁÁ
ÁÁÁÁ
.25 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
R26,R27
ÁÁÁ
ÁÁÁ
2
4.8k Ω Resistor
ÁÁÁÁ
ÁÁÁÁ
1 W
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
U1
ÁÁÁ
ÁÁÁ
1
Quad 2 input NAND
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MC74HC00AN
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
U2,U3
ÁÁÁ
ÁÁÁ
2
MOSFET Driver
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MC34151P
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
U4,U5
ÁÁÁ
ÁÁÁ
2
MOS T urn-off Device
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MDC1000A
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
U6
ÁÁÁ
ÁÁÁ
1
3-pin Voltage Regulator
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Motorola
ÁÁÁÁÁÁ
ÁÁÁÁÁÁ
MC78L05ACP
MOTOROLA
7
AN1319
Additional decoupling capacitors across each half-bridge
provide high frequency current for reverse recovery. Any
sharp voltage spikes created during reverse recovery are
smoothed out and kept from propagating to the other
half-bridge creating unwanted noise. These decoupling
capacitors should be physically placed as close to the
half-bridge as possible.
The PCB layout is also a very important design
consideration. Care must be taken to minimize the source
inductance and any stray inductance in the high current
paths. This is done by keeping the high current traces as
wide and as short as possible. Another rule to follow is that
the low current ground traces or trace should tie to the high
current trace at one central grounding point. Typically the
sources of the power transistors are used as the grounding
point. If using current sense resistors, the leads terminating
to ground must be the central grounding point.
The dynamic design challenges are solved simply by
employing a gate drive impedance strategy. The different
gate impedances in Figures 2 and 3 are optimized to control
the turn-on di/dt, shoot-through current and diode snap.
Faster turn-off of the bottom FETs minimizes turn-off
switching losses.
BOARD DESCRIPTION
Evaluation board DEVB151 was designed to be an
electronic building block that interfaces a microcontroller to
a motor. This board translates HCMOS logic signals, like
those from a microprocessor or microcontroller, to motor
turning power. DEVB151 can drive a brushed DC motor in
both directions or drive one phase of a stepper motor. Four
inputs to the board control the gates of H-Bridge configured
FETs. The outputs of the board include + and – terminals
for the motor and current-sense terminals for each
half-bridge. A single voltage power source is all that is
required to operate the board. A silk-screen plot and a full
schematic are shown in Figures 7 and 8, respectively. The
board content is listed in Table 1.
All control inputs and current sense outputs are on the
left side of the board. Inputs A TOP, A BOT, B TOP, and B
BOT each correspond to a similarly labeled power FET and
have positive logic. For example, when B TOP is logic 1 its
corresponding transistor is on. To prevent an accidental
simultaneous conduction of either half-bridge (A TOP=A
BOT=1 or B TOP=B BOT=1), protection circuitry was added
to the design. Cross-coupled NAND gates disable the bottom
transistor when the top transistor is on. This protection
scheme has another advantage. Inputs A BOT and B BOT
can be tied together and share the same PWM signal. The
logic of the upper transistors determines which bottom
transistor is pulse width modulated. Resistors and zeners are
additions to the board inputs to deter static damage of the
NAND gates. The NAND inputs are directly compatible with
5 volt HCMOS logic and form a direct interface to
microcontrollers and microprocessors.
The voltages at output terminals A CS and B CS are the
representations of the current through each half-bridge,
respectively. Current is related to the voltage present at
these terminals by a ratio of 100 amps per volt. To incorporate
a single-current sense voltage, jumper J1, can be installed.
This ties the current sense resistors from each half-bridge
together. In this case, the output voltage at A CS or B CS
is related to the current by a ratio of 200 amps per volt. The
voltage representation of the currents at these terminals is
very noisy . To obtain a clean sense voltage, low pass filtering
is recommended before sampling. CS GND terminal is
ground for the current sense outputs. Along with this ground,
two more terminals are labeled ground. One is used for the
ground lead from the microcontroller and the other is
available as an instrument grounding point.
All power connections are on the right side of the board.
Power to the board is brought in on the +B and GND
terminals. The power outputs to the motor are the +M and
– M terminals.
The heart of DEVB151 is the MPM3017. The MPM3017
is made up of four N-channel power MOSFETs which have
an RDS(on) rating of 40 mΩ maximum, a breakdown voltage
of 60 volts and are energy rated. The remainder of operating
specifications are listed in Table 2.
Application of DEVB151 is shown in the diagram of Figure
9. An 8 bit microcontroller, such as the MC68HC11, can be
readily programmed to generate the required signals to
operate this evaluation board. This microcontroller contains
a general purpose timer used to perform the time-intensive
tasks of generating a PWM signal. The cross-coupled NAND
gates at the inputs of DEVB151 allow the use of only one
PWM signal. The direction signals can simply be outputs from
an available parallel port. In Figure 8, two bits of port B are
used as the direction signals, and port A, pin 6 is the output
carrying the PWM signal.
Table 2. Electrical Characteristics
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Characteristic
ÁÁÁÁÁ
ÁÁÁÁÁ
Symbol
ÁÁÁÁ
ÁÁÁÁ
Min
ÁÁÁÁ
ÁÁÁÁ
Typ
ÁÁÁÁ
ÁÁÁÁ
Max
ÁÁÁÁÁ
ÁÁÁÁÁ
Units
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Input voltage
ÁÁÁÁÁ
ÁÁÁÁÁ
+B
ÁÁÁÁ
ÁÁÁÁ
18
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
48
ÁÁÁÁÁ
ÁÁÁÁÁ
Volts
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Peak motor current
ÁÁÁÁÁ
ÁÁÁÁÁ
IPK
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
30
ÁÁÁÁÁ
ÁÁÁÁÁ
Amps
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Continuous motor current
ÁÁÁÁÁ
ÁÁÁÁÁ
IC
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
8
ÁÁÁÁÁ
ÁÁÁÁÁ
Amps
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Minimum logic 1 input voltage
ÁÁÁÁÁ
ÁÁÁÁÁ
VIH
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
2.7
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁ
ÁÁÁÁÁ
Volts
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Maximum logic 0 input voltage
ÁÁÁÁÁ
ÁÁÁÁÁ
VIL
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
2.0
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁ
ÁÁÁÁÁ
Volts
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Power dissipation
ÁÁÁÁÁ
ÁÁÁÁÁ
PD
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
7
ÁÁÁÁÁ
ÁÁÁÁÁ
Watts
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Sense voltage
ÁÁÁÁÁ
ÁÁÁÁÁ
Vsense
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
10
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁ
ÁÁÁÁÁ
mV/A
* Additional heat sinking will increase the maximum power dissipation rating.
8
MOTOROLA AN1319
Figure 9. Application Block Diagram
ÏÏÏ
ÏÏÏ
ÏÏÏ
ÏÏ
ÏÏ
ÏÏ
ÏÏ
ÏÏÏÏ
ÏÏÏÏ
ÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏ
+B
+M
–M
GND
Atop
Btop
Abot
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
Bbot
MC68HC11
PB1
PB0
PA6
ÏÏ
ÏÏ
ÏÏ
+
–
Brushed
DC Motor
dir
pwm
dir ′
DEVB151
CONCLUSIONS
N-channel half-bridges increase performance of motor
drive systems over that of complementary half-bridges.
However, the dynamic issues of the design remain constant
for both topologies. Shoot-through current and diode snap
are managed by relatively simple circuit solutions. These
circuit solutions stem from the optimization of the gate
impedances for separate turn-on and turn-off speeds. The
additional voltage needed to drive the upper half of the
N-channel half-bridges above the motor voltage is derived
from a charge pump.
DEVB151 is more efficiently used if the bottom transistors
are pulse-width modulated rather than the upper transistors.
The top transistors can be pulse-width modulated, however,
due to limitations of the high-side gate drive, top FET turn-on
speed is slower than that of the bottom FETs. The slower
turn-on speed leads to greater switching losses.
Losses in the charge pump circuitry limit the low end
supply voltage to 15 volts, therefore DEVB151 does not
address the 12 volt market. However , implementing a voltage
tripler, a modified charge pump, will allow operation down
to 12 volts.
Looking at DEVB151 as a building block between a
microcontroller and a motor, the board is kept simple and
is protected from accidental misuse. DEVB151 only needs
a single voltage source from which different voltage levels
are supplied to the various internal devices. The
cross-coupled NAND gates prohibit the user from
accidentally destroying the power transistors on the board.
All inputs and outputs are clearly labeled and are fairly
self-explanatory.
REFERENCES
1) Berringer, Ken, “One-Horsepower Off-Line Brushless
Permanent Magnet Motor Drive,” Power Conversion and
Intelligent Motion, June 1990
2) Schultz, Warren, “Interfacing Microcomputers to
Fractional Horsepower Motors,” Motorola Application
Note AN1300
3) Schultz, Warren, “Drive Techniques for High Side
N-Channel MOSFETs,” Power Conversion and Intelligent
Motion, June 1987
4) Motorola Power MOSFET Transistor Data, DL135 Rev
3, 1989
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specifically disclaims any and all liability , including without limitation consequential or incidental damages. “Typical” parameters can and do vary in different
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AN1319/D
◊
*AN1319/D*