LTC1857/LTC1858/LTC1859 8-Channel, 12-/14-/16-Bit, 100ksps SoftSpan A/D Converters with Shutdown FEATURES DESCRIPTION n The LTC(R)1857/LTC1858/LTC1859 are 8-channel, low power, 12-/14-/16-bit, 100ksps, analog-to-digital converters (ADCs). These SoftSpanTM ADCs can be softwareprogrammed for 0V to 5V, 0V to 10V, 5V or 10V input spans and operate from a single 5V supply. The 8-channel multiplexer can be programmed for single-ended inputs or pairs of differential inputs or combinations of both. In addition, all channels are fault protected to 25V. A fault condition on any channel will not affect the conversion result of the selected channel. n n n n n n n n n n n Sample Rate: 100ksps 8-Channel Multiplexer with 25V Protection Single 5V Supply Software-Programmable Input Ranges: 0V to 5V, 0V to 10V, 5V or 10V Single Ended or Differential 3LSB INL for the LTC1859, 1.5LSB INL for the LTC1858, 1LSB INL for the LTC1857 Power Dissipation: 40mW (Typ) SPI/MICROWIRETM Compatible Serial I/O Power Shutdown: Nap and Sleep Signal-to-Noise Ratio: 87dB (Typ) for the LTC1859 Operates with Internal or External Reference Internal Synchronized Clock 28-Pin SSOP Package APPLICATIONS n n n n An onboard high performance sample-and-hold and precision reference minimize external components. The low 40mW power dissipation is made even more attractive with two user selectable power shutdown modes. DC specifications include 3LSB INL for the LTC1859, 1.5LSB INL for the LTC1858 and 1LSB for the LTC1857. The internal clock is trimmed for 5s maximum conversion time and the sampling rate is guaranteed at 100ksps. A separate convert start input and data ready signal (BUSY) ease connections to FIFOs, DSPs and microprocessors. Industrial Process Control Multiplexed Data Acquisition Systems High Speed Data Acquisition for PCs Digital Signal Processing L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. SoftSpan is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION 100kHz, 12-Bit/14-Bit/16-Bit Sampling ADC LTC1859 Typical INL Curve 2.0 1.5 P CONTROL LINES 1.0 10F 10F 3V TO 5V 5V 5V 10F INL (LSB) SOFTWARE-PROGRAMMABLE SINGLE-ENDED OR DIFFERENTIAL INPUTS (0V TO 5V, 0V TO 10V, 5V OR 10V) COM CONVST CH0 LTC1857/ RD CH1 LTC1858/ SCK CH2 LTC1859 SDI CH3 DGND CH4 SDO CH5 BUSY CH6 OVDD DVDD CH7 AVDD MUXOUT+ MUXOUT- AGND3 ADC+ AGND2 ADC- REFCOMP AGND1 VREF 0.5 0 -0.5 -1.0 -1.5 2.5V 1F 10F -2.0 -32768 -16384 0 CODE 16384 32767 1859 TA02 185789fa 1 LTC1857/LTC1858/LTC1859 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Supply Voltage (OVDD = DVDD = AVDD = VDD) .............6V Ground Voltage Difference DGND, AGND1, AGND2, AGND3 ........................0.3V Analog Input Voltage ADC+, ADC- (Note 3) ................. (AGND1 - 0.3V) to (AVDD + 0.3V) CH0-CH7, COM ..................................................25V Digital Input Voltage (Note 4).......(DGND - 0.3V) to 10V Digital Output Voltage ..(DGND - 0.3V) to (DVDD + 0.3V) Power Dissipation ...............................................500mW Operating Temperature Range LTC1857C/LTC1858C/LTC1859C .............. 0C to 70C LTC1857I/LTC1858I/LTC1859I.............. -40C to 85C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C COM 1 28 CONVST CH0 2 27 RD CH1 3 26 SCK CH2 4 25 SDI CH3 5 24 DGND CH4 6 23 SDO CH5 7 22 BUSY CH6 8 21 OVDD CH7 9 20 DVDD MUXOUT+ 10 19 AVDD MUXOUT- 11 18 AGND3 ADC+ 12 17 AGND2 ADC- 13 16 REFCOMP AGND1 14 15 VREF G PACKAGE 28-LEAD PLASTIC SSOP TJMAX = 110C, JA = 95C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL LTC1857CG#PBF PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC1857CG#TRPBF 28-Lead Plastic SSOP 0C to 70C LTC1857IG#PBF LTC1857IG#TRPBF 28-Lead Plastic SSOP -40C to 85C LTC1858CG#PBF LTC1858CG#TRPBF 28-Lead Plastic SSOP 0C to 70C LTC1858IG#PBF LTC1858IG#TRPBF 28-Lead Plastic SSOP -40C to 85C LTC1859CG#PBF LTC1859CG#TRPBF 28-Lead Plastic SSOP 0C to 70C LTC1859IG#PBF LTC1859IG#TRPBF 28-Lead Plastic SSOP -40C to 85C LEAD BASED FINISH TAPE AND REEL PACKAGE DESCRIPTION TEMPERATURE RANGE LTC1857CG LTC1857CG#TR 28-Lead Plastic SSOP 0C to 70C LTC1857IG LTC1857IG#TR 28-Lead Plastic SSOP -40C to 85C LTC1858CG LTC1858CG#TR 28-Lead Plastic SSOP 0C to 70C LTC1858IG LTC1858IG#TR 28-Lead Plastic SSOP -40C to 85C LTC1859CG LTC1859CG#TR 28-Lead Plastic SSOP 0C to 70C LTC1859IG LTC1859IG#TR 28-Lead Plastic SSOP -40C to 85C PART MARKING Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 185789fa 2 LTC1857/LTC1858/LTC1859 CONVERTER AND MULTPLEXER CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. MUXOUT connected to ADC inputs. (Notes 5, 6) LTC1857 PARAMETER CONDITIONS MIN Resolution l 12 No Missing Codes l 12 Transition Noise TYP (Notes 7, 15) l Differential Linearity Error (Note 15) l Bipolar Zero Error (Note 8) l Bipolar Zero Error Drift MIN Bipolar Full-Scale Error Drift External Reference Internal Reference Unipolar Full-Scale Error External Reference (Note 11) l Internal Reference (Note 11) Unipolar Full-Scale Error Drift External Reference Internal Reference 17 l l Input Common Mode Rejection Ratio LSB 4 LSB 28 0.1 LSB ppm/C 4 6 10 LSB 15 25 LSB 1 1 ppm/C 1.2 2 8 0.35 0.45 0.15 0.4 0.1 0.4 2.5 7 2.5 7 10 15 0.45 0.75 0.25 0.85 0.2 0.75 2.5 7 LSB % % ppm/C ppm/C 5 5 Unipolar Mode Bipolar Mode 3 6 2.5 7 Unipolar Full-Scale Error Match Bits LSBRMS -2 0.1 2.5 7 Bipolar Full-Scale Error Match UNITS Bits 1 1.5 1 External Reference (Note 11) Internal Reference (Note 11) MAX 1.5 -1 9 l TYP 15 0.26 1 Unipolar Zero Error Match Bipolar Full-Scale Error MIN 16 1 -1 l Unipolar Zero Error Drift MAX 14 0.1 (Note 8) TYP LTC1859 14 Bipolar Zero Error Match Input Common Mode Range MAX 0.06 Integral Linearity Error Unipolar Zero Error LTC1858 2.5 7 12 LSB % % ppm/C ppm/C 15 LSB 0 to 10 10 0 to 10 10 0 to 10 10 V V 96 96 96 dB ANALOG INPUT The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5) PARAMETER CONDITIONS Analog Input Range CH0 to CH7, COM 0 to 5, 0 to 10 5, 10 V V ADC+, ADC- (Note 3) 0 to 2.048 0 to 4.096 ADC- 1.024 ADC- 2.048 V V V V Impedance MIN MAX UNITS CH0 to CH7, COM Unipolar Bipolar 42 31 k k MUXOUT+, MUXOUT- Unipolar Bipolar 10 5 k k Hi-Z k 5 pF 0V to 2.048V, 1.024V 0V to 4.096V, 2.048V 24 12 pF pF Hold Mode ADC+, ADC- 4 pF ADC+, ADC- Capacitance TYP CH0 to CH7, COM Sample Mode ADC+, ADC- Input Leakage Current ADC+, ADC-, CONVST = Low l 1 A 185789fa 3 LTC1857/LTC1858/LTC1859 DYNAMIC ACCURACY The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. MUXOUT connected to ADC inputs. (Notes 5, 12) LTC1857 SYMBOL PARAMETER CONDITIONS MIN S/(N + D) Signal-to-(Noise + Distortion) Ratio 1kHz Input Signal THD Total Harmonic Distortion 1kHz Input Signal, First Five Harmonics TYP LTC1858 MAX MIN TYP LTC1859 MAX MIN TYP MAX UNITS 74 83 87 dB -101 -101 -101 dB Peak Harmonic or Spurious Noise 1kHz Input Signal -103 -103 -103 dB Channel-to-Channel Isolation 1kHz Input Signal -120 -120 -120 dB -3dB Input Bandwidth Aperture Delay Aperture Jitter 1 1 1 -70 -70 -70 60 Transient Response Full-Scale Step (Note 9) Overvoltage Recovery (Note 13) 60 4 MHz ns 60 ps 4 150 4 150 s 150 ns INTERNAL REFERENCE CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5) PARAMETER CONDITIONS VREF Output Voltage IOUT = 0 VREF Output Temperature Coefficient IOUT = 0 VREF Output Impedance -0.1mA IOUT 0.1mA VREFCOMP Output Voltage IOUT = 0 l MIN TYP MAX UNITS 2.475 2.5 2.525 V 10 ppm/C 8 k 4.096 V DIGITAL INPUTS AND DIGITAL OUTPUTS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5) SYMBOL PARAMETER CONDITIONS MIN VIH High Level Input Voltage VDD = 5.25V l VIL Low Level Input Voltage VDD = 4.75V l IIN Digital Input Current VIN = 0V to VDD l CIN Digital Input Capacitance VOH High Level Output Voltage VOL Low Level Output Voltage IOZ VDD = 4.75V, IO = -10A, OVDD = VDD VDD = 4.75V, IO = -200A, OVDD = VDD l VDD = 4.75V, IO = 160A, OVDD = VDD VDD = 4.75V, IO = 1.6mA, OVDD = VDD l Hi-Z Output Leakage VOUT = 0V to VDD, RD = High l TYP MAX UNITS 2.4 V 0.8 V 10 A 5 pF 4.74 V V 4 0.05 0.10 0.4 V V 10 A COZ Hi-Z Output Capacitance RD = High 15 pF ISOURCE Output Source Current VOUT = 0V -10 mA ISINK Output Sink Current VOUT = VDD 10 mA POWER REQUIREMENTS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5) PARAMETER CONDITIONS MIN TYP MAX UNITS Positive Supply Voltage (Notes 9 and 10) 4.75 5 5.25 V CONVST = 0V or 5V 8 5.5 8 13 8 15 CONVST = 0V or 5V 40 27.5 40 Positive Supply Current Nap Mode Sleep Mode Power Dissipation Nap Mode Sleep Mode l mA mA A mW mW W 185789fa 4 LTC1857/LTC1858/LTC1859 TIMING CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5) SYMBOL PARAMETER CONDITIONS fSAMPLE(MAX) Maximum Sampling Frequency Through CH0 to CH7 Inputs Through ADC+, ADC- Only tCONV Conversion Time tACQ Acquisition Time MIN l TYP MAX 100 kHz kHz 166 l Through CH0 to CH7 Inputs Through ADC+, ADC- Only l l 4 5 s 4 s s 20 MHz 1 fSCK SCK Frequency (Note 14) tr SDO Rise Time See Test Circuits 6 ns tf SDO Fall Time See Test Circuits 6 ns t1 CONVST High Time t2 CONVST to BUSY Delay t3 SCK Period l 50 ns t4 SCK High l 10 ns t5 SCK Low l 10 l CL = 25pF, See Test Circuits 0 UNITS 40 l ns 15 30 ns ns Delay Time, SCK to SDO Valid CL = 25pF, See Test Circuits l Time from Previous SDO Data Remains Valid After SCK CL = 25pF, See Test Circuits l t8 SDO Valid After RD CL = 25pF, See Test Circuits l t9 RD to SCK Setup Time l 20 ns t10 SDI Setup Time Before SCK l 0 ns t11 SDI Hold Time After SCK l 7 t12 SDO Valid Before BUSY RD = Low, CL = 25pF, See Test Circuits l 5 t13 Bus Relinquish Time See Test Circuits l t6 t7 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All voltage values are with respect to ground with DGND, AGND1, AGND2 and AGND3 wired together unless otherwise noted. Note 3: When these pin voltages are taken below ground or above AVDD = DVDD = OVDD = VDD, they will be clamped by internal diodes. This product can handle currents of greater than 100mA below ground or above VDD without latchup. Note 4: When these pin voltages are taken below ground they will be clamped by internal diodes. This product can handle currents of greater than 100mA below ground without latchup. These pins are not clamped to VDD. Note 5: VDD = 5V, fSAMPLE = 100kHz, tr = tf = 5ns unless otherwise specified. Note 6: Linearity, offset and full-scale specifications apply for a singleended analog MUX input with respect to ground or ADC+ with respect to ADC- tied to ground. Note 7: Integral nonlinearity is defined as the deviation of a code from a straight line passing through the actual end points of the transfer curve. The deviation is measured from the center of the quantization band. 25 5 45 20 11 ns ns 30 ns ns 20 10 ns 30 ns Note 8: Bipolar zero error is the offset voltage measured from - 0.5LSB when the output code flickers between 0000 0000 0000 0000 and 1111 1111 1111 1111 for the LTC1859, between 00 0000 0000 0000 and 11 1111 1111 1111 for the LTC1858 and between 0000 0000 0000 and 1111 1111 1111 for the LTC1857. Unipolar zero error is the offset voltage measured from 0.5LSB when the output codes flicker between 0000 0000 0000 0000 and 0000 0000 0000 0001 for the LTC1859, between 00 0000 0000 0000 and 00 0000 0000 0001 for the LTC1858 and between 0000 0000 0000 and 0000 0000 0001 for the LTC1857. Note 9: Guaranteed by design, not subject to test. Note 10: Recommended operating conditions. Note 11: Full-scale bipolar error is the worst case of -FS or +FS untrimmed deviation from ideal first and last code transitions, divided by the full-scale range, and includes the effect of offset error. For unipolar full-scale error, the deviation of the last code transition from ideal, divided by the full-scale range, and includes the effect of offset error. Note 12: All Specifications in dB are referred to a full-scale 10V input. Note 13: Recovers to specified performance after (2 * FS) input overvoltage. Note 14: t6 of 45ns maximum allows fSCK up to 10MHz for rising capture with 50% duty cycle and fSCK up to 20MHz for falling capture (with 5ns setup time for the receiving logic). Note 15: The specification is referred to the 10V input range. 185789fa 5 LTC1857/LTC1858/LTC1859 TYPICAL PERFORMANCE CHARACTERISTICS LTC1859 Typical INL Curve 0 1.5 1.5 1.0 1.0 0.5 0.5 0 -0.5 MAGNITUDE (dB) 2.0 DNL (LSB) 0 -0.5 -1.0 -1.0 -1.5 -1.5 -2.0 -32768 -16384 0 CODE 16384 -2.0 -32768 32767 -16384 1859 G01 LTC1859 SINAD vs Input Frequency 0 CODE 16384 TOTAL HARMONIC DISTORTION (dB) 86 84 82 80 78 74 1.0 -80 -90 -110 10 INPUT FREQUENCY (kHz) 1 100 10 INPUT FREQUENCY (kHz) 1 -1.0 -50 -25 0 25 50 TEMPERATURE (C) 75 100 1959 G07 -0.5 -25 0 25 50 TEMPERATURE (C) 75 0.04 2.515 2.510 2.505 2.500 2.495 2.490 2.485 2.480 -50 100 Change in REFCOMP Voltage vs Load Current CHANGE IN REFCOMP VOLTAGE (V) INTERNAL REFERENCE VOLTAGE (V) -0.5 UNIPOLAR MODE 1959 G06 2.520 BIPOLAR MODE 0 Internal Reference Voltage vs Temperature 1.0 0 BIPOLAR MODE 1859 G05 LTC1859 Channel-to-Channel Gain Error Matching vs Temperature UNIPOLAR MODE 0.5 -1.0 -50 100 1859 G04 0.5 10 15 20 25 30 35 40 45 50 FREQUENCY (kHz) LTC1859 Channel-to-Channel Offset Error Matching vs Temperature -100 76 5 1869 G03 -70 88 CHANNEL-TO-CHANNEL GAIN ERROR MATCHING (LSBs) 0 32767 1859 G02 LTC1859 Total Harmonic Distortion vs Input Frequency 90 fSAMPLE = 100kHz fIN = 1kHz SINAD = 86.95dB THD = -101.42dB -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 CHANNEL-TO-CHANNEL OFFSET ERROR MATCHING (LSBs) INL (LSB) 2.0 SINAD (dB) LTC1859 Nonaveraged 4096-Point FFT Plot LTC1859 Typical DNL Curve -25 0 50 25 TEMPERATURE (C) 75 100 1859 G08 0.02 0 -0.02 -0.04 -50 -40 -30 -20 -10 LOAD CURRENT (mA) 0 10 1859 G09 185789fa 6 LTC1857/LTC1858/LTC1859 TYPICAL PERFORMANCE CHARACTERISTICS LTC1859 Power Supply Feedthrough vs Ripple Frequency fSAMPLE = 100kHz VRIPPLE = 60mV -30 -40 -50 -60 fSAMPLE = 100kHz 8.5 8.0 7.5 -70 -80 100 1k 10k 100k RIPPLE FREQUENCY (Hz) 1M 1859 G10 Supply Current vs Temperature 9.0 POSITIVE SUPPLY CURRENT (mA) -20 Supply Current vs Supply Voltage 9.0 SUPPLY CURRENT (mA) POWER SUPPLY FEEDTHROUGH (dB) -10 7.0 4.5 5 5.25 4.75 SUPPLY VOLTAGE (V) 5.5 fSAMPLE = 100kHz 8.5 8.0 7.5 7.0 -50 -25 1859 G11 0 25 50 TEMPERATURE (C) 75 100 1859 G12 PIN FUNCTIONS COM (Pin 1): Common Input. This is the reference point for all single-ended inputs. It must be free of noise and is usually connected to the analog ground plane. AGND1 (Pin 14): Analog Ground. CH0 (Pin 2): Analog MUX Input. CH2 (Pin 4): Analog MUX Input. REFCOMP (Pin 16): Reference Buffer Output. Bypass to analog ground with a 10F tantalum and a 0.1F ceramic capacitor. Nominal output voltage is 4.096V. CH3 (Pin 5): Analog MUX Input. AGND2 (Pin 17): Analog Ground. CH4 (Pin 6): Analog MUX Input. AGND3 (Pin 18): Analog Ground. This is the substrate connection. CH1 (Pin 3): Analog MUX Input. CH5 (Pin 7): Analog MUX Input. CH6 (Pin 8): Analog MUX Input. CH7 (Pin 9): Analog MUX Input. MUXOUT + (Pin 10): Positive MUX Output. Output of the analog multiplexer. Connect to ADC+ for normal operation. VREF (Pin 15): 2.5V Reference Output. Bypass to analog ground with a 1F tantalum capacitor. AVDD (Pin 19): 5V Analog Supply. Bypass to analog ground with a 0.1F ceramic and a 10F tantalum capacitor. DVDD (Pin 20): 5V Digital Supply. Bypass to digital ground with a 0.1F ceramic and a 10F tantalum capacitor. MUXOUT- (Pin 11): Negative MUX Output. Output of the analog multiplexer. Connect to ADC- for normal operation. OVDD (Pin 21): Positive Supply for the Digital Output Buffers (3V to 5V). Bypass to digital ground with a 0.1F ceramic and a 10F tantalum capacitor. ADC + (Pin 12): Positive Analog Input to the Analog-toDigital Converter. BUSY (Pin 22): Output shows converter status. It is low when a conversion is in progress. ADC- (Pin 13): Negative Analog Input to the Analog-toDigital Converter. SDO (Pin 23): Serial Data Output. 185789fa 7 LTC1857/LTC1858/LTC1859 PIN FUNCTIONS RD (Pin 27): Read Input. This active low signal enables the digital output pin SDO. DGND (Pin 24): Digital Ground. SDI (Pin 25): Serial Data Input. CONVST (Pin 28): Conversion Start. This active high signal starts a conversion on its rising edge. SCK (Pin 26): Serial Data Clock. FUNCTIONAL BLOCK DIAGRAM AVDD DVDD MUX ADDRESS AND RANGE CH0 CONVST CONTROL LOGIC CH1 INTERNAL CLOCK INPUT MUX AND RANGE SELECT * * * SDI BUSY SCK + 12-/14-/16-BIT SAMPLING ADC CH7 - COM RD DATA OUT SERIAL I/O OVDD SDO 4.096V 2.5V REFERENCE 8k MUXOUT- MUXOUT+ ADC+ 1.6384X ADC- 1859 BD VREF AGND1 REFCOMP AGND2 AGND3 DGND TEST CIRCUITS Load Circuits for Access Timing Load Circuits for Output Float Delay 5V 5V 1k DN 1k DN 1k 25pF (A) Hi-Z TO VOH AND VOL TO VOH DN DN 1k 25pF (B) Hi-Z TO VOL AND VOH TO VOL 1859 TC01 (A) VOH TO Hi-Z 25pF 25pF (B) VOL TO Hi-Z 1859 TC02 185789fa 8 LTC1857/LTC1858/LTC1859 TIMING DIAGRAMS t2 (CONVST to BUSY Delay) t2 t1 (For Short Pulse Mode) CONVST 2.4V t1 BUSY 50% 50% CONVST 0.4V 1859 TD02 1859 TD01 t6 (Delay Time, SCKn to SDO Valid) t7 (Time from Previous Data Remains Valid After SCKn) t6 t7 t3, t4, t5 (SCK Timing) SCK t4 0.4V t5 SCK 2.4V 0.4V SDO t3 1859 TD03 1859 TD04 t9 (RDn to SCK Setup Time) t8 (SDO Valid After RDn) t8 RD RD SDO t9 0.4V 0.4V Hi-Z 2.4V 0.4V 2.4V SCK 1959 TD06 1859 TD05 t10 (SDI Setup Time Before SCKl) t11 (SDI Hold Time After SCKl) t11 t10 2.4V SCK SDI 2.4V SCK 2.4V 0.4V 2.4V 0.4V SDI 1859 TD08 1859 TD07 t12 (SDO Valid Before BUSYl, RD = 0) t13 (BUS Relinquish Time) t13 t12 2.4V BUSY SDO 2.4V RD B15 SDO 2.4V 90% 10% Hi-Z 1859 TD10 1859 TD09 185789fa 9 LTC1857/LTC1858/LTC1859 OPERATION OVERVIEW The LTC1857/LTC1858/LTC1859 are innovative, multichannel ADCs that provide software-selectable input ranges for each of their eight input channels. Using on-chip resistors and switches, it provides an attenuation and offset that can be programmed for each channel on the fly. The precisely trimmed attenuators ensure accurate input ranges. Because they precede the multiplexer, errors due to multiplexer on-resistance are eliminated. The input word that selects the input channel also selects the desired input range for that channel. The available ranges are 0V to 5V, 0V to 10V (unipolar), 5V and 10V (bipolar). They are achieved with the ADC running on a single 5V supply. In addition to the range selection, single ended or differential inputs may be selected for each channel or pair of channels. Finally, overrange protection is provided for unselected channels. An overrange condition on an unused channel will not affect the conversion result on the selected channel. CONVERSION DETAILS The analog signals applied at the MUX input channels are rescaled by the resistor divider network formed by R1, R2 and R3 as shown below. The rescaled signals appear on the MUXOUT (Pins 10, 11) which are also connected to the ADC inputs (Pins 12, 13) under normal operation. REFCOMP BIPOLAR MUX INPUT During the conversion, the internal differential 12-/14/16-bit capacitive DAC output is sequenced by the SAR from the most significant bit (MSB) to the least significant bit (LSB). The input is successively compared with the binary weighted charges supplied by the differential capacitive DAC. Bit decisions are made by a high speed comparator. At the end of a conversion, the DAC output balances the analog input (ADC + - ADC-). The SAR contents (a 16-bit data word) which represents the difference of ADC+ and ADC- are loaded into the 12-/14-/16-bit shift register. DRIVING THE ANALOG INPUTS The LTC1857/LTC1858/LTC1859 use a successive approximation algorithm and an internal sample-and-hold circuit to convert an analog signal to a 12-/14-/16-bit serial output respectively. The ADCs are complete with a precision reference and an internal clock. The control logic provides easy interface to microprocessors and DSPs. (Please refer to the Digital Interface section for the data format.) R1 25k Before starting a conversion, an 8-bit data word is clocked into the SDI input on the first eight rising SCK edges to select the MUX address, input range and power down mode. The ADC enters acquisition mode on the falling edge of the sixth clock in the 8-bit data word and ends on the rising edge of the CONVST signal which also starts a conversion (see Figure 7). A minimum time of 4s will provide enough time for the sample-and-hold capacitors to acquire the analog signal. Once a conversion cycle has begun, it cannot be restarted. R3 10k CH SEL MUXOUT R2 17k The nominal input ranges for the LTC1857/LTC1858/ LTC1859 are 0V to 5V, 0V to 10V, 5V and 10V and the MUX inputs are overvoltage protected to 25V. The input impedance is typically 42k in unipolar mode and 31k in bipolar mode, therefore, it should be driven with a low impedance source. Wideband noise coupling into the input can be minimized by placing a 3000pF capacitor at the input as shown in Figure 2. An NPO-type capacitor gives the lowest distortion. Place the capacitor as close to the device input pin as possible. If an amplifier is to be used to drive the input, care should be taken to select an amplifier with adequate accuracy, linearity and noise for the application. The following list is a summary of the op amps that are suitable for driving the LTC1857/LTC1858/LTC1859. More detailed information is available in the Linear Technology data books and online at www.linear.com. LT(R)1007: Low noise precision amplifier. 2.7mA supply current 5V to 15V supplies. Gain bandwidth product 8MHz. DC applications. 1859 AI03 185789fa 10 LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION AVDD DVDD MUX ADDRESS AND RANGE CH0 CONVST CONTROL LOGIC CH1 INTERNAL CLOCK INPUT MUX AND RANGE SELECT * * * SDI BUSY SCK + 12-/14-/16-BIT SAMPLING ADC CH7 - COM RD DATA OUT SERIAL I/O OVDD SDO 4.096V 2.5V REFERENCE 8k MUXOUT- MUXOUT+ ADC+ 1.6384X ADC- 1859 BD VREF AGND1 REFCOMP AGND2 AGND3 DGND Figure 1. LTC1857/LTC1858/LTC1859 Simplified Equivalent Circuit AIN+ AIN- LT1792: Single, low noise JFET input op amp, 5V supplies. CH0 3000pF CH1 * * * * MUXOUT+ MUXOUT- ADC+ ADC- 1859 F02 Figure 2. Analog Input Filtering LT1227: 140MHz video current feedback amplifier. 10mA supply current. 5V to 15V supplies. Low noise and low distortion. LT1468/LT1469: Single and dual 90MHz, 16-bit accurate op amp. Good AC/DC specs. LT1677: Single, low noise op amp. Rail-to-rail input and output. Up to 15V supplies. LT1793: Single, low noise JFET input op amp, 10pA bias current, 5V supplies. LT1881/LT1882: Dual and quad, 200pA bias current, railto-rail output op amps. Up to 15V supplies. LT1844/LT1885: Dual and quad, 400pA bias current, rail-to-rail output op amps. Up to 15V supplies. Faster response and settling time. INTERNAL VOLTAGE REFERENCE The LTC1857/LTC1858/LTC1859 have an on-chip, temperature compensated, curvature corrected, bandgap reference, which is factory trimmed to 2.50V. The full-scale range of the LTC1857/LTC1858/LTC1859 is equal to 5V, 0V to 5V, 10V or 0V to 10V. The output of the reference is connected to the input of a gain of 1.6384x buffer through an 8k resistor (see Figure 3). The input to the buffer or 185789fa 11 LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION the output of the reference is available at VREF (Pin 15). The internal reference can be overdriven with an external reference if more accuracy is needed. The buffer output drives the internal DAC and is available at REFCOMP (Pin 16). The REFCOMP pin can be used to drive a steady DC load of less than 2mA. Driving an AC load is not recommended because it can cause the performance of the converter to degrade. 15 VREF 2.5V 8k 1F 2.5V REFERENCE 12-/14-/16-BIT CAPACITIVE DAC 1.6384X BUFFER 16 REFCOMP 4.096V 0.1F 1859 F03 10F Figure 3. Internal or External Reference Source For minimum code transition noise the VREF pin and the REFCOMP pin should each be decoupled with a capacitor to filter wideband noise from the reference and the buffer. UNIPOLAR / BIPOLAR OPERATION Figure 4a shows the ideal input/output characteristics for the LTC1859. The code transitions occur midway 1LSB = 111...111 between successive integer LSB values (i.e., 0.5LSB, 1.5LSB, 2.5LSB, ... FS - 1.5LSB). The output code is natural binary with 1LSB = FS/65536. Figure 4b shows the input/output transfer characteristics for the bipolar mode in two's complement format. FULL SCALE AND OFFSET In applications where absolute accuracy is important, offset and full-scale errors can be adjusted to zero during a calibration sequence. Offset error must be adjusted before full-scale error. Zero offset is achieved by adjusting the offset applied to the "-" input. For single-ended inputs, this offset should be applied to the COM pin. For differential inputs, the "-" input is dictated by the MUX address. For unipolar zero offset error, apply 0.5LSB (actual voltage will vary with input span selected) to the "+" input and adjust the offset at the "-" input until the output code flickers between 0000 0000 0000 0000 and 0000 0000 0000 0001 for the LTC1859, between 00 0000 0000 0000 and 00 0000 0000 0001 for the LTC1858 and between 0000 0000 0000 and 0000 0000 0001 for the LTC1857. For bipolar zero error, apply - 0.5LSB (actual voltage will vary with input span selected) to the "+" input and adjust the offset at the "-" input until the output code flickers between 0000 0000 0000 0000 and 1111 1111 1111 1111 for the LTC1859, between 00 0000 0000 0000 and FS 65536 011...111 111...110 1LSB = 011...110 111...100 OUTPUT CODE OUTPUT CODE 111...101 UNIPOLAR ZERO 000...011 FS 65536 BIPOLAR ZERO 000...001 000...000 111...111 111...110 000...010 100...001 000...001 100...000 000...000 0V 1 LSB FS - 1LSB INPUT VOLTAGE (V) 1859 F4a Figure 4a. Unipolar Transfer Characteristics (UNI = 1) -FS/2 -1 0V 1 LSB LSB INPUT VOLTAGE (V) FS/2 - 1LSB 1859 F4b Figure 4b. Bipolar Transfer Characteristics (UNI = 0) 185789fa 12 LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION 11 1111 1111 1111 for the LTC1858 and between 0000 0000 0000 and 1111 1111 1111 for the LTC1857. For bipolar inputs, an input voltage of FS - 1.5LSBs should be applied to the "+" input and the appropriate reference adjusted until the output code flickers between 0111 1111 1111 1110 and 0111 1111 1111 1111 for the LTC1859, between 01 1111 1111 1110 and 01 1111 1111 1111 for the LTC1858 and between 0111 1111 1110 and 0111 1111 1111 for the LTC1857. These adjustments as well as the factory trims affect all channels. The channel-to-channel offset and gain error matching are guaranteed by design to meet the specifications in the Converter Characteristics table. 1600 1400 1200 COUNT As mentioned earlier, the internal reference is factory trimmed to 2.50V. To make sure that the reference buffer gain is not compensating for trim errors in the reference, REFCOMP is trimmed with an accurate external 2.5V reference applied to VREF. For unipolar inputs, an input voltage of FS - 1.5LSBs should be applied to the "+" input and the appropriate reference adjusted until the output code flickers between 1111 1111 1111 1110 and 1111 1111 1111 1111 for the LTC1859, between 11 1111 1111 1110 and 11 1111 1111 1111 for the LTC1858 and between 1111 1111 1110 and 1111 1111 1111 for the LTC1857. 1800 1000 800 600 400 200 0 -4 -3 -2 -1 1 0 CODE 2 3 4 1859 F05 Figure 5. LTC1859 Histogram for 4096 Conversions 3V Input/Output Compatible The LTC1857/LTC1858/LTC1859 operate on a 5V supply, which makes the devices easy to interface to 5V digital systems. These devices can also interface to 3V digital systems: the digital input pins (SCK, SDI, CONVST and RD) of the LTC1857/LTC1858/LTC1859 recognize 3V or 5V inputs. The LTC1857/LTC1858/LTC1859 have a dedicated output supply pin (OVP) that controls the output swings of the digital output pins (SDO, BUSY) and allows the part to interface to either 3V or 5V digital systems. The output is two's complement binary for bipolar mode and offset binary for unipolar mode. DC PERFORMANCE Timing and Control One way of measuring the transition noise associated with a high resolution ADC is to use a technique where a DC signal is applied to the input of the MUX and the resulting output codes are collected over a large number of conversions. For example in Figure 5 the distribution of output code is shown for a DC input that has been digitized 4096 times. The distribution is Gaussian and the RMS code transition is about 1LSB for the LTC1859. Conversion start and data read are controlled by two digital inputs: CONVST and RD. To start a conversion and put the sample-and-hold into the hold mode bring CONVST high for no less than 40ns. Once initiated it cannot be restarted until the conversion is complete. Converter status is indicated by the BUSY output and this is low while the conversion is in progress. DIGITAL INTERFACE Internal Clock The ADC has an internal clock that is trimmed to achieve a typical conversion time of 4s. No external adjustments are required and, with the maximum acquisition time of 4s, throughput performance of 100ksps is assured. Figures 6a and 6b show two different modes of operation for the LTC1859. For the 12-bit LTC1857 and 14-bit LTC1858, the last four and two bits of the SDO will output zeros respectively. In mode 1 (Figure 6a), RD is tied low. The rising edge of CONVST starts the conversion. The data outputs are always enabled. The MSB of the data output is available after the conversion. In mode 2 (Figure 6b), CONVST and RD are tied together. The rising edge of the CONVST signal starts the conversion. Data outputs are in 185789fa 13 14 Hi-Z DON'T CARE Hi-Z DON'T CARE t5 SGL/ DIFF t4 1 t10 t3 t4 1 B15 (MSB) t8 t5 t10 t3 SGL/ DIFF t8 B15 (MSB) t9 t12 B14 ODD/ SIGN t11 2 SELECT 0 4 UNI 5 GAIN 6 B12 B11 B10 B9 NAP 7 B8 SLEEP 8 tACQ B1 DON'T CARE 15 t7 B0 (LSB) t6 16 t2 t1 tCONV t12 B15 (MSB) SGL/ DIFF 1 B14 ODD/ SIGN 2 SELECT 0 4 UNI 5 GAIN 6 NAP 7 SLEEP SELECT 0 4 UNI 5 GAIN 6 B13 B12 B11 B10 SHIFT CONFIGURATION WORD IN SELECT 1 3 B9 NAP 7 B8 SLEEP 8 tACQ B1 DON'T CARE 15 B0 (LSB) t7 t6 16 t2 Hi-Z tCONV t13 B15 (MSB) SGL/ DIFF 1 B14 ODD/ SIGN 2 B13 B12 B11 B10 B9 SELECT 0 4 UNI 5 GAIN 6 NAP 7 SLEEP 8 B8 B13 B12 B11 B10 B9 B8 SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN SELECT 1 3 8 SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN SELECT 1 3 Figure 6a. Mode 1 for the LTC1859*. CONVST Starts a Conversion, Data Output is Always Enabled (RD = 0) B13 SHIFT CONFIGURATION WORD IN SELECT 1 3 SELECT 0 4 UNI 5 GAIN 6 B13 B12 B11 B10 SHIFT CONFIGURATION WORD IN SELECT 1 3 B9 NAP 7 B8 SLEEP 8 tACQ t7 B0 (LSB) t6 16 t2 Hi-Z tCONV t1 B15 (MSB) SGL/ DIFF 1 B14 ODD/ SIGN 2 Figure 7. Operating Sequence for the LTC1859* B1 DON'T CARE 15 t13 SELECT 0 4 UNI 5 GAIN 6 NAP 7 SLEEP 8 B13 B12 B11 B10 B9 B8 SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN SELECT 1 3 Figure 6b. Mode 2 for the LTC1859*. CONVST and RD Tied Together. CONVST Starts a Conversion, Data is Read by RD B14 ODD/ SIGN t11 2 B14 B15 (MSB) t11 2 ODD/ SIGN t5 t10 t3 SGL/ DIFF t9 DON'T CARE t4 1 *For the 12-bit LTC1857 and 14-bit LTC1858, the last four and two bits of the SDO will output zeros respectively. BUSY CONVST SDO SDI SCK RD BUSY SDO SDI SCK CONVST = RD BUSY CONVST SDO SDI SCK RD = 0 B1 15 16 B0 (LSB) DON'T CARE 16 B0 (LSB) DON'T CARE 16 B0 (LSB) DON'T CARE B1 15 B1 15 1859 F07 Hi-Z 1859 F06b Hi-Z 1859 F06a LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION 185789fa LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION three-state at this time. When the conversion is complete (BUSY goes high), CONVST and RD go low to enable the data output for the previous conversion. next data transfer cycle. As shown below, the result of a conversion is delayed by one conversion from the input word requesting it. SERIAL DATA INPUT (SDI) INTERFACE SDI SDI WORD 1 SDI WORD 2 SDI WORD 3 The LTC1857/LTC1858/LTC1859 communicate with microprocessors and other external circuitry via a synchronous, full duplex, 3-wire serial interface (see Figure 7). The shift clock (SCK) synchronizes the data transfer with each bit being transmitted on the falling SCK edge and captured on the rising SCK edge in both transmitting and receiving systems. The data is transmitted and received simultaneously (full duplex). SDO SDO WORD 0 SDO WORD 1 SDO WORD 2 DATA TRANSFER tCONV A/D CONVERSION 1859 * AI01 tCONV A/D CONVERSION DATA TRANSFER INPUT DATA WORD The LTC1857/LTC1858/LTC1859 8-bit data word is clocked into the SDI input on the first eight rising SCK edges. Further inputs on the SDI pin are then ignored until the next conversion. The eight bits of the input word are defined as follows: An 8-bit input word is shifted into the SDI input which configures the LTC1857/LTC1858/LTC1859 for the next conversion. Simultaneously, the result of the previous conversion is output on the SDO line. At the end of the data exchange the requested conversion begins by applying a rising edge on CONVST. After tCONV, the conversion is complete and the results will be available on the INPUT RANGE SGL/ DIFF ODD SIGN SELECT 1 SELECT 0 UNI GAIN SLEEP NAP POWER DOWN SELECTION MUX ADDRESS 1859 AI02 Table 1. Multiplexer Channel Selection MUX ADDRESS SGL/ ODD SELECT DIFF SIGN 1 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 DIFFERENTIAL CHANNEL SELECTION 0 1 + - 2 3 + - + 0,1 { 2,3 { 4,5 { 6,7 { + (-) - (+) + (-) - (+) + (-) - (+) + (-) - (+) 5 6 7 - + - - + - + - + - 4 Differential CHANNEL 4 MUX ADDRESS SGL/ ODD SELECT DIFF SIGN 1 0 1 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 8 Single-Ended CHANNEL 0 1 2 3 4 5 6 7 + + + + + + + + COM (-) + SINGLE-ENDED CHANNEL SELECTION 0 1 2 0,1 { + - 2,3 { - + + + + + 4 5 6 7 COM (-) 4 5 6 7 COM + - - - - - - - - + + + + + + + Combinations of Differential and Single-Ended CHANNEL 3 Changing the MUX Assignment "On the Fly" 4,5 { 6,7 { + - + - COM (UNUSED) 1ST CONVERSION 4,5 { - + 6 7 + + COM (-) 2ND CONVERSION 1859 F08 Figure 8. Examples of Multiplexer Options on the LTC1857/LTC1858/LTC1859 185789fa 15 LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION MUX ADDRESS The first four bits of the input word assign the MUX configuration for the requested conversion. For a given channel selection, the converter will measure the voltage between the two channels indicated by the + and - signs in the selected row of Table 1. Note that in differential mode (SGL/DIFF = 0) measurements are limited to four adjacent input pairs with either polarity. In single-ended mode, all input channels are measured with respect to COM. Both the "+" and "-" inputs are sampled simultaneously so common mode noise is rejected. INPUT RANGE (UNI, GAIN) The fifth and sixth input bits (UNI, GAIN) determine the input range for the conversion. When UNI is a logical one, a unipolar conversion will be performed. When UNI is a logical zero, a bipolar conversion will result. The GAIN input bit determines the input span for the conversion. When GAIN is a logical one, either 0V to 10V or 10V input spans will be selected depending on UNI. When GAIN is a logical zero, either 0V to 5V or 5V input spans will be chosen. The input ranges for different UNI and GAIN inputs are shown in Table 2. Table 2. Input Range Selection UNI GAIN INPUT RANGE 0 0 5V 1 0 0V to 5V 0 1 10V 1 1 0V to 10V POWER DOWN SELECTION (NAP, SLEEP) The last two bits of the input word (Nap and Sleep) determine the power shutdown mode of the LTC1857/LTC1858/ LTC1859. See Table 3. Nap mode is selected when Nap = 1 and Sleep = 0. The previous conversion result will be clocked out and a conversion will occur before entering the Nap mode. The Nap mode starts at the end of the conversion which is indicated by the rising edge of the BUSY signal. Nap mode lasts until the falling edge of the 2nd SCK (see Figure 9). Automatic nap will be achieved if Nap = 1 is selected each time an input word is written to the ADC. Table 3. Power Down Selection NAP SLEEP POWER DOWN MODE 0 0 Power On 1 0 Nap X 1 Sleep Sleep mode will occur when Sleep = 1 is selected, regardless of the selection of the Nap input. The previous conversion result can be clocked out and the Sleep mode will start on the falling edge of the last (16th) SCK. Notice that the CONVST should stay either high or low in sleep mode (see Figure 10). To wake up from the sleep mode, apply a rising edge on the CONVST signal and then apply Sleep = 0 on the next SDI word and the part will wake up on the falling edge of the last (16th) SCK (see Figure 11). In Sleep mode, all bias currents are shut down and only the power on reset circuit and leakage currents (about 10A) remain. Sleep mode wake-up time is dependent on the value of the capacitor connected to the REFCOMP (Pin 16). The wake-up time is typically 40ms with the recommended 10F capacitor connected on the REFCOMP pin. DYNAMIC PERFORMANCE FFT (Fast Fourier Transform) test techniques are used to test the ADC's frequency response, distortion and noise at the rated throughput. By applying a low distortion sine wave and analyzing the digital output using an FFT algorithm, the ADC's spectral content can be examined for frequencies outside the fundamental. Figure 12 shows a typical LTC1859 FFT plot which yields a SINAD of 87dB and THD of - 101dB. 185789fa 16 tCONV DON'T CARE tCONV DON'T CARE B15 (MSB) SGL/ DIFF SGL/ DIFF 1 B15 (MSB) 3 SELECT 0 4 UNI 5 GAIN 6 B13 B14 ODD/ SIGN 2 B14 ODD/ SIGN 2 SELECT 1 3 B11 SELECT 0 4 B10 UNI 5 8 B9 GAIN 6 B8 B12 B11 B10 A/D RESULT NOT VALID B9 B8 SLEEP = 1 8 SELECT 0 4 UNI 5 GAIN 6 B13 B12 B10 SLEEP tCONV Hi-Z NAP B15 MSB SGL/ DIFF 1 B1 DON'T CARE 15 B0 (LSB) 16 SELECT 1 B9 NAP 7 B8 SLEEP = 0 8 B1 DON'T CARE 15 WAKE-UP TIME B0 (LSB) 16 READY tCONV 3 SELECT 0 4 UNI 5 GAIN 6 NAP 7 SLEEP 8 15 B14 B13 B15 (MSB) SGL/ DIFF 1 B14 ODD/ SIGN 2 B12 B13 SELECT 0 4 B10 UNI 5 B9 GAIN 6 B8 NAP 7 8 SLEEP tACQ B1 B12 B11 B10 B9 B8 16 B0 (LSB) DON'T CARE SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN SELECT 1 3 SLEEP B11 SHIFT A/D RESULT OUT FROM PREVIOUS CONVERSION AND NEW CONFIGURATION WORD IN ODD/ SIGN 2 Figure 11. Wake Up from Sleep Mode for the LTC1859* A/D RESULT NOT VALID B11 SHIFT WAKE-UP CONFIGURATION WORD IN SELECT 1 3 B0 (LSB) 16 Figure 10. Sleep Mode Operation for the LTC1859* CONVST SHOULD STAY EITHER HIGH OR LOW IN SLEEP MODE B13 7 tACQ B1 DON'T CARE 15 Figure 9. Nap Mode Operation for the LTC1859* NAP NAP = 1 SLEEP = 0 7 SHIFT WAKE-UP CONFIGURATION WORD IN B12 SHIFT CONFIGURATION WORD IN SELECT 1 SGL/ DIFF 1 B15 (MSB) B14 ODD/ SIGN 2 *For the 12-bit LTC1857 and 14-bit LTC1858, the last four and two bits of the SDO will output zeros respectively. Hi-Z DON'T CARE 1 16 B1 B0 (LSB) DON'T CARE 15 1859 F10 1859 F09 Hi-Z 1859 F11 APPLICATIONS INFORMATION BUSY CONVST SDO SDI SCK RD BUSY CONVST SDO SDI SCK RD BUSY CONVST SDO SDI SCK RD LTC1857/LTC1858/LTC1859 185789fa 17 LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION SIGNAL-TO-NOISE RATIO The Signal-to-Noise and Distortion Ratio (SINAD) is the ratio between the RMS amplitude of the fundamental input frequency to the RMS amplitude of all other frequency components at the A/D output. The output is band limited to frequencies from above DC and below half the sampling frequency. Figure 12 shows a typical SINAD of 87dB with a 100kHz sampling rate and a 1kHz input. TOTAL HARMONIC DISTORTION Total Harmonic Distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as: THD = 20log V22 + V32 + V42 ... + VN2 V1 MAGNITUDE (dB) where V1 is the RMS amplitude of the fundamental frequency and V2 through VN are the amplitudes of the second through Nth harmonics. BOARD LAYOUT, POWER SUPPLIES AND DECOUPLING Wire wrap boards are not recommended for high resolution or high speed A/D converters. To obtain the best performance from the LTC1857/LTC1858/LTC1859, a printed circuit board is required. Layout for the printed circuit board should ensure the digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital track alongside an analog signal track or underneath the ADC. The analog input should be screened by AGND. In applications where the MUX is connected to the ADC, it is possible to get noise coupling into the ADC from the trace connecting the MUXOUT to the ADC. Therefore, reducing the length of the traces connecting the MUXOUT pins (Pins 10, 11) to the ADC pins (Pins 12, 13) can minimize the problem. The unused MUX inputs should be grounded to prevent noise coupling into the inputs. Figure 13 shows the power supply grounding that will help obtain the best performance from the 12-bit/14-bit/16-bit ADCs. Pay particular attention to the design of the analog and digital ground planes. The DGND pin of the LTC1857/ 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 fSAMPLE = 100kHz fIN = 1kHz SINAD = 86.95dB THD = -101.42dB 0 5 10 15 30 20 25 FREQUENCY (kHz) 35 40 45 50 1859 F12 Figure 12. LTC1859 Nonaveraged 4096 Point FFT Plot 185789fa 18 LTC1857/LTC1858/LTC1859 APPLICATIONS INFORMATION LTC1858/LTC1859 can be tied to the analog ground plane. Placing the bypass capacitor as close as possible to the power supply pins, the reference and reference buffer output is very important. Low impedance common returns for these bypass capacitors are essential to low noise operation of the ADC, and the foil width for these tracks should be as wide as possible. Also, since any potential difference in + - grounds between the signal source and ADC appears as an error voltage in series with the input signal, attention should be paid to reducing the ground circuit impedance as much as possible. The digital output latches and the onboard sampling clock have been placed on the digital ground plane. The two ground planes are tied together at the power supply ground connection. LTC1857/ LTC1858/ CH0 LTC1859 10 12 CH1 MUXOUT+ ADC+ CH2 LTC1857/LTC1858/LTC1859 CH3 CH4 ADC- MUXOUT- VREF REFCOMP AGND AVDD DVDD DGND 11 13 CH5 CH6 15 16 14, 17, 18 19 20 24 CH7 1F 10F 10F 10F COM DIGITAL SYSTEM OVDD 21 10F ANALOG GROUND PLANE 1859 F13 Figure 13. Power Supply Grounding Practice PACKAGE DESCRIPTION G Package 28-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 1.25 0.12 7.8 - 8.2 5.3 - 5.7 0.42 0.03 RECOMMENDED SOLDER PAD LAYOUT 5.00 - 5.60** (.197 - .221) 0.65 BSC 2.0 (.079) MAX 9.90 - 10.50* (.390 - .413) 28 27 26 25 24 23 22 21 20 19 18 17 16 15 0 - 8 0.09 - 0.25 (.0035 - .010) 0.55 - 0.95 (.022 - .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE 7.40 - 8.20 (.291 - .323) 0.65 (.0256) BSC 0.22 - 0.38 0.05 (.009 - .015) (.002) TYP MIN *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 G28 SSOP 0204 185789fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 LTC1857/LTC1858/LTC1859 TYPICAL APPLICATION 5V 5V 10F 0.1F 10F 19 DVDD AVDD 1 COM CONVST 28 MUX ADDRESS AND RANGE 2 CH0 SINGLE-ENDED OR DIFFERENTIAL CHANNEL SELECTION (SEE TABLE 1) INPUT RANGES: 0V TO 5V 0V TO 10V 5V AND 10V SDI 25 CONTROL LOGIC 3 CH1 BUSY 22 INTERNAL CLOCK INPUT MUX AND RANGE SELECT * * * 0.1F 20 8-BIT SERIAL DATA INPUT SCK 26 16 SHIFT CLOCK CYCLES + 9 CH7 12-/14-/16-BIT SAMPLING ADC RD 27 DATA OUT OVDD 21 - 4.096V 16-BIT SERIAL DATA OUT 1.6384X 8k MUXOUT- 14 MUXOUT+ 11 10 ADC+ 12 ADC- VREF 13 15 AGND2 AGND3 DGND REFCOMP 16 1F 0.1F SDO 23 2.5V REFERENCE AGND1 3V TO 5V 10F SERIAL I/O 10F 17 18 1859 TA03 24 0.1F RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1417 14-Bit, 400ksps Serial ADC 5V or 5V, 20mW, 81dB SINAD and -95dB THD LTC1418 14-Bit, 200ksps, Single 5V or 5V ADC 15mW, Serial/Parallel I/O LTC1604 16-Bit, 333ksps, 5V ADC 90dB SINAD, 220mW Power Dissipation, Pin Compatible with LTC1608 LTC1605 16-Bit, 100ksps, Single 5V ADC 10V Inputs, 55mW, Byte or Parallel I/O, Pin Compatible with LTC1606 LTC1606 16-Bit, 250ksps, Single 5V ADC 10V Inputs, 75mW, Byte or Parallel I/O, Pin Compatible with LTC1605 LTC1608 16-Bit, 500ksps, 5V ADC 90dB SINAD, 270mW Power Dissipation, Pin Compatible with LTC1604 LTC1609 16-Bit, 200ksps Serial ADC Configurable Unipolar/Bipolar Input, Single 5V Supply LTC1850/LTC1851 10-Bit/12-Bit, 8-Channel, 1.25Msps ADC Programmable MUX and Sequencer, Parallel I/O LTC1852/LTC1853 10-Bit/12-Bit, 8-Channel, 400ksps ADC Single 3V-5V, Programmable MUX and Sequencer, Parallel I/O LTC1864/LTC1865 16-Bit, 1-/2-Channel, 250ksps ADC in MSOP Single 5V Supply, 850A with Autoshutdown LTC1864L/LTC1865L 3V, 16-Bit, 1-/2-Channel, 150ksps ADC in MSOP Single 3V Supply, 450A with Autoshutdown LTC1588/LTC1589/ LTC1592 12-/14-/16-Bit, Serial, SoftSpan IOUT DACs Software-Selectable Spans, 1LSB INL/DNL LTC1595 16-Bit Serial Multiplying IOUT DAC in SO-8 1LSB Max INL/DNL, Low Glitch, DAC8043 16-Bit Upgrade LTC1596 16-Bit Serial Multiplying IOUT DAC 1LSB Max INL/DNL, Low Glitch, AD7543/DAC8143 16-Bit Upgrade LTC1597 16-Bit Parallel, Multiplying DAC 1LSB Max INL/DNL, Low Glitch, 4 Quadrant Resistors LTC1650 16-Bit Serial VOUT DAC Low Power, Low Gritch, 4-Quadrant Multiplication Single/Dual 90MHz, 22V/s, 16-Bit Accurate Op Amp Low Input Offset : 75V/125V Sampling ADCs DACs Op Amps LT1468/LT1469 185789fa 20 Linear Technology Corporation LT 1007 REV A * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2004