Low-Power, 13-Bit Voltage-Output DACs with Serial Interface

Transcription

1 ; Rev 1; 12/96 Low-Power, 13-Bit oltage-output ACs General escription The combine a low-power, voltageoutput, 13-bit digital-to-analog converter (AC) and a precision output amplifier in an 8-pin µ or IP package. The operates from a single +5 supply and the operates from a single +3.3 supply. Both devices draw only 28µA of supply current. The output amplifier s inverting input is available to the user, allowing specific gain configuratio, remote seing, and high output current capability. This makes the ideal for a wide range of applicatio, including industrial process control. Other features include a software shutdown and power-on reset. The serial interface is compatible with either SPI / QSPI or Microwire. The AC has a double-buffered input, organized as an input register followed by a AC register. A 16-bit serial word loads data into the input register. The AC register can be updated independently or simultaneously with the input register. All logic inputs are TTL/CMOS-logic compatible and buffered with Schmitt triggers to allow direct interfacing to optocouplers. Applicatio Industrial Process Controls Automatic Test Equipment igital Offset and Gain Adjustment Motion Control Remote Industrial Controls Microprocessor-Controlled Systems Functional iagram Features 13-Bit AC with Configurable Output Amplifier +5 Single-Supply Operation () +3.3 Single-Supply Operation () Low Supply Current:.24mA Normal Operation 2µA Shutdown Mode Available in 8-Pin µ Power-On Reset Clears AC Output to SPI/QSPI and Microwire Compatible Schmitt-Trigger igital Inputs for irect Optocoupler Interface Ordering Information PART TEMP. RANGE PIN-PACKAGE INL (LSB) ACPA BCPA C to +7 C C to +7 C 8 Plastic IP 8 Plastic IP ±1/2 ±1 ACUA C to +7 C 8 µ ±1/2 BCUA C to +7 C 8 µ ±1 BC/ C to +7 C ice* ±1 Ordering Information continued at end of data sheet. Contact factory for availability. *ice are tested at TA = +25 C, C parameters only. Pin Configuration GN REF TOP IEW FB CONTROL AC REGISTER INPUT REGISTER AC IN GN REF IN 16-BIT SHIFT REGISTER 4 IP/µ 5 FB SPI and QSPI are registered trademarks of Motorola, Inc. Microwire is a registered trademark of National Semiconductor Corp. Maxim Integrated Products 1 For free samples & the latest literature: or phone

2 Low-Power, 13-Bit oltage-output ACs ABSOLUTE IMUM RATINGS to GN...-.3, +6 REF,, FB to GN to ( +.3) igital Inputs to GN to +6 Continuous Current into Any Pin...±2mA Continuous Power issipation (T A = +7 C) Plastic IP (derate 6.9mW/ C above +7 C)...552mW µ (derate 4.mW/ C above +7 C)...33mW CERIP (derate 8.mW/ C above +7 C)...64mW Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditio beyond those indicated in the operational sectio of the specificatio is not implied. Exposure to absolute maximum rating conditio for extended periods may affect device reliability. ELECTRICAL CHARACTERISTI: Operating Temperature Ranges _C_A/_C_A... C to +7 C _E_A/_E_A...-4 C to +85 C BMJA/BMJA C to +125 C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1sec)...+3 C ( = +5 ±1%, REF = 2.5, GN =, R L = 5kΩ, C L = 1pF, T A = T to T, unless otherwise noted. Typical values are at T A = +25 C. Output buffer connected in unity-gain configuration (Figure 8).) PARAMETER SYMBOL STATIC PERFORMANCE ANALOG SECTION Resolution Integral Nonlinearity (Note 1) ifferential Nonlinearity Offset Error Offset-Error Tempco Gain-Error Tempco CONITIONS MJA Guaranteed monotonic Power-Supply Rejection Ratio PSRR REFERENCE INPUT Reference Input Range REF Reference Input Resistance R REF MULTIPLYING-MOE PERFORMANCE Reference -3dB Bandwidth Reference Feedthrough Signal-to-Noise Plus SINA istortion Ratio IGITAL INPUTS Input High oltage IH Input Low oltage IL Input Leakage Current I IN Input Capacitance C IN N INL NL OS TC OS A B Gain Error (Note 1) GE -.5 ±6 Code dependent, minimum at code 1555 hex REF =.67p-p Input code = all s, REF = 3.6p-p at 1kHz REF = 1p-p at 25kHz, code = full scale IN = or TYP ±.5 UNITS Bits ±1. LSB ±2. ±1. LSB ±.3 ±8 m ±.5 8 ppm/ C LSB ppm/ C µ/ kω khz db db µa pf 2

3 Low-Power, 13-Bit oltage-output ACs ELECTRICAL CHARACTERISTI: (continued) ( = +5 ±1%, REF = 2.5, GN =, R L = 5kΩ, C L = 1pF, T A = T to T, unless otherwise noted. Typical values are at T A = +25 C. Output buffer connected in unity-gain configuration (Figure 8).) PARAMETER IGITAL YNAMIC INPUTS PERFORMANCE oltage Output Slew Rate Output Settling Time Output oltage Swing Current into FB Time to alid Operation on Start-Up igital Feedthrough POWER SUPPLIES Supply oltage Supply Current Supply Current in Shutdown Reference Current in Shutdown TIG CHARACTERISTI Clock Period Pulse Width High Pulse Width Low Fall to Rise Setup Time Rise to Rise Hold Time IN Setup Time IN Hold Time Rise to Fall elay Rise to Rise Hold Time Pulse Width High SYMBOL SR I t CP t CH t CL t S t H t S t H t t 1 t W To ±1/2LSB, STEP = 2.5 Rail-to-rail (Note 2) CONITIONS =, IN = 1kHz TYP.6 16 to.1 ±.1 n-s (Note 3).28.4 ma (Note 3) 4 2 µa.1 ±.5 µa UNITS /µs µs µa µs Note 1: Guaranteed from code 22 to code 8191 in unity-gain configuration. Note 2: Accuracy is better than 1LSB for = 8m to - 1m, guaranteed by a power-supply rejection test at the end points. Note 3: R L =, digital inputs at GN or. 3

4 Low-Power, 13-Bit oltage-output ACs ELECTRICAL CHARACTERISTI: ( = to +3.6, REF = 1.25, GN =, R L = 5kΩ, C L = 1pF, T A = T to T, unless otherwise noted. Typical values are at T A = +25 C. Output buffer connected in unity-gain configuration (Figure 8).) PARAMETER SYMBOL CONITIONS TYP STATIC PERFORMANCE ANALOG SECTION Resolution N 13 A ±1 Integral Nonlinearity INL B ±2 (Note 4) MJA ±4 ifferential Nonlinearity NL Guaranteed monotonic ±1. Offset Error OS ±.3 ±8 Offset-Error Tempco TC OS 6 Gain Error (Note 4) GE -.5 ±6 Gain-Error Tempco 1 Power-Supply Rejection Ratio PSRR 6 REFERENCE INPUT Reference Input Range REF Reference Input Resistance R REF Code dependent, minimum at code 1555 hex 14 2 MULTIPLYING-MOE PERFORMANCE ( = +3.3) Reference -3dB Bandwidth REF =.67p-p 65 Reference Feedthrough Input code = all s, REF = 1.9p-p at 1kHz -84 Signal-to-Noise Plus istortion Ratio SINA REF = 1p-p at 25kHz, code = full scale 72 IGITAL INPUTS Input High oltage IH 2.4 Input Low oltage IL.6 Input Leakage Current I IN IN = or.1 ±.5 Input Capacitance C IN 8 YNAMIC PERFORMANCE oltage Output Slew Rate SR.6 Output Settling Time To ±1/2LSB, STEP = Output oltage Swing Rail-to-rail (Note 5) to Current into FB.1 ±.1 Time to alid Operation on Start-Up 2 UNITS Bits LSB LSB m ppm/ C LSB ppm/ C µ/ kω khz db db µa pf /µs µs µa µs igital Feedthrough =, IN = 1kHz 5 n-s POWER SUPPLIES Supply oltage Supply Current I (Note 6).24.4 ma Supply Current in Shutdown (Note 6) µa Reference Current in Shutdown.1 ±.5 µa 4

5 Low-Power, 13-Bit oltage-output ACs ELECTRICAL CHARACTERISTI: (continued) ( = to +3.6, REF = 1.25, GN =, R L = 5kΩ, C L = 1pF, T A = T to T, unless otherwise noted. Typical values are at T A = +25 C. Output buffer connected in unity-gain configuration (Figure 8).) PARAMETER SYMBOL TIG CHARACTERISTI Clock Period t CP Pulse Width High t CH Pulse Width Low t CL Fall to Rise Setup Time t S Rise to Rise Hold Time IN Setup Time IN Hold Time Rise to Fall elay Rise to Rise Hold Time Pulse Width High t H t S t H t t 1 t W CONITIONS TYP UNITS Note 4: Guaranteed from code 44 to code 8191 in unity-gain configuration. Note 5: Accuracy is better than 1LSB for = 8m to - 15m, guaranteed by a power-supply rejection test at the end points. Note 6: R L =, digital inputs at GN or. 5

6 Low-Power, 13-Bit oltage-output ACs Typical Operating Characteristics ( only, = +5, R L = 5kΩ, C L = 1pF, T A = +25 C, unless otherwise noted.) INL (LSB) POWER-OWN SUPPLY CURRENT (µa) SIGNAL AMPLITUE (db) POWER-OWN SUPPLY CURRENT vs. TEMPERATURE INTEGRAL NONLINEARITY vs. REFERENCE OLTAGE REFERENCE OLTAGE () TEMPERATURE ( C) PUT FFT PLOT FREQUENCY (khz) REF = 3.6p-p COE = FULL SCALE f IN = 1kHz FULL-SCALE PUT () RELATIE PUT (db) SUPPLY CURRENT (µa) REFERENCE OLTAGE INPUT FREQUENCY RESPONSE 5k 1M 1.5M 2M 2.5M 3M FREQUENCY (Hz) SUPPLY CURRENT vs. SUPPLY OLTAGE SUPPLY OLTAGE () FULL-SCALE PUT vs. LOA.1k.1k 1k 1k 1k 1M 1M LOA (Ω) SUPPLY CURRENT (µa) SIGNAL AMPLITUE (db) TH + NOISE (db) SUPPLY CURRENT vs. TEMPERATURE 4 38 R L = TOTAL HARMONIC ISTORTION PLUS NOISE vs. FREQUENCY REF = 2.5 C + 1p-p SINE COE = FULL SCALE FREQUENCY (khz) TEMPERATURE ( C) REFERENCE FEETHROUGH AT 1kHz REFERENCE INPUT SIGNAL PUT FEETHROUGH FREQUENCY (khz) a/9b 6

7 Low-Power, 13-Bit oltage-output ACs Typical Operating Characteristics (continued) ( only, = +5, R L = 5kΩ, C L = 1pF, T A = +25 C, unless otherwise noted.) 5/div, AC COUPLE 1m/div MAJOR-CARRY TRANSITION (continued) -1, 2/div, AC COUPLE 1m/div COE = 496 IGITAL FEETHROUGH (f = 1kHz) -11 1µs/div = 5 2µs/div YNAMIC RESPONSE -12 1/div GN 1µs/div GAIN = 2, SWITCHING FROM COE TO 84 7

8 Low-Power, 13-Bit oltage-output ACs Typical Operating Characteristics (continued) ( only, = +3.3, R L = 5kΩ, C L = 1pF, T A = +25 C, unless otherwise noted.) INL (LSB) POWER-OWN SUPPLY CURRENT (µa) INTEGRAL NONLINEARITY vs. REFERENCE OLTAGE REFERENCE OLTAGE () POWER-OWN SUPPLY CURRENT vs. TEMPERATURE TEMPERATURE ( C) RELATIE PUT (db) SUPPLY CURRENT (µa) REFERENCE OLTAGE INPUT FREQUENCY RESPONSE -2 1k 5k 1M 1.5M 2M 2.5M FREQUENCY (Hz) SUPPLY CURRENT vs. SUPPLY OLTAGE SUPPLY OLTAGE () SUPPLY CURRENT (µa) TH + NOISE (db) R L = SUPPLY CURRENT vs. TEMPERATURE TEMPERATURE ( C) TOTAL HARMONIC ISTORTION PLUS NOISE vs. FREQUENCY REF = 1 C +.5p-p SINE COE = FULL SCALE FREQUENCY (khz) SIGNAL AMPLITUE (db) PUT FFT PLOT FREQUENCY (khz) REF = 1.9p-p COE = FULL SCALE f IN = 1kHz -19 FULL-SCALE PUT () FULL-SCALE PUT vs. LOA 1 1k 1k 1k 1M 1M LOA (Ω) -2 SIGNAL AMPLITUE (db) REFERENCE FEETHROUGH AT 1kHz REFERENCE INPUT SIGNAL PUT FEETHROUGH FREQUENCY (khz) -21 8

9 Low-Power, 13-Bit oltage-output ACs Pin escription PIN NAME FUNCTION 1 AC Output oltage 2 Chip-Select Input. Active low. 3 IN Serial-ata Input 4 Serial-Clock Input 5 FB AC Output Amplifier Feedback 6 REF Reference oltage Input 7 GN Ground 8 Positive Power Supply R R R 2R 2R 2R 2R 2R REF AGN SHOWN FOR ALL 1s ON AC Figure 1. Simplified AC Circuit iagram FB etailed escription The contain a 13-bit, voltage-output digital-to-analog converter (AC) that is easily addressed using a simple 3-wire serial interface. It includes a 16-bit shift register, and has a doubledbuffered input composed of an input register and a AC register (see Functional iagram). In addition to the voltage output, the amplifier s negative input is available to the user. The AC is an inverted R-2R ladder network that converts a 13-bit digital input into an equivalent analog output voltage in proportion to the applied reference voltage input. Figure 1 shows a simplified circuit diagram of the AC. Reference Inputs The reference input accepts positive C and AC signals. The voltage at the reference input sets the fullscale output voltage for the AC. The reference input voltage range is to ( - 1.4). The output voltage () is represented by a digitally programmable voltage source as: = (REF x NB / 8192 ) x Gain where NB is the numeric value of the AC s binary input code ( to 8191), REF is the reference voltage, and Gain is the externally set voltage gain. The impedance at the reference input is code dependent, ranging from a low value of 14kΩ when the AC has an input code of 1555 hex, to a high value exceeding several giga ohms (leakage currents) with an input code of hex. Because the input impedance at the reference pin is code dependent, load regulation of the reference source is important. The REF reference input has a 14kΩ guaranteed minimum input impedance. A voltage reference with a load regulation of 6ppm/mA, such as the 873, would typically deviate by.62lsb (.9LSB worst case) when driving the reference input at 2.5. In shutdown mode, the s REF input enters a high-impedance state with a typical input leakage current of.1µa. The reference input capacitance is also code dependent and typically ranges from 15pF (with an input code of all s) to 5pF (with an input code of all 1s). Output Amplifier The s AC output is internally buffered by a precision amplifier with a typical slew rate of.6/µs. Access to the output amplifier s inverting input provides the user greater flexibility in output gain setting/signal conditioning (see the Applicatio Information section). With a full-scale traition at the output, the typical settling time to ±1/2LSB is 16µs when loaded with 5kΩ in parallel with 1pF (loads less than 2kΩ degrade performance). The output amplifier s output dynamic respoes and settling performances are shown in the Typical Operating Characteristics. 9

10 Low-Power, 13-Bit oltage-output ACs Shutdown Mode The feature a software-programmable shutdown that reduces supply current to a typical value of 4µA. Writing 111XXXXXXXXXXXXX as the input-control word puts the in shutdown mode (Table 1). In shutdown mode, the output amplifier and the reference input enter a high-impedance state. The serial interface remai active. ata in the input registers is retained in shutdown, allowing the to recall the output state prior to entering shutdown. Exit shutdown mode by either recalling the previous configuration or by updating the AC with new data. When powering up the device or bringing it out of shutdown, allow 2µs for the output to stabilize. Serial-Interface Configuratio The s 3-wire serial interface is compatible with both Microwire (Figure 2) and SPI /QSPI (Figure 3). The serial input word coists of three control bits followed by 13 data bits (MSB first), as shown in Figure 4. The 3-bit control code determines the s respoe outlined in Table 1. The s digital inputs are double buffered. epending on the command issued through the serial interface, the input register can be loaded without affecting the AC register, the AC register can be loaded directly, or the AC register can be updated from the input register (Table 1). Serial-Interface escription The require 16 bits of serial data. Table 1 lists the serial-interface programming commands. For certain commands, the 13 data bits are don t cares. ata is sent MSB first and can be sent in two 8-bit packets or one 16-bit word ( must remain low until 16 bits are traferred). The serial data is composed of three control bits (C2, C1, C), followed by the 13 data bits (Figure 4). The 3-bit control code determines: The register to be updated The configuration when exiting shutdown Figure 5 shows the serial-interface timing requirements. The chip-select pin () must be low to enable the AC s serial interface. When is high, the interface control circuitry is disabled. must go low at least ts before the rising serial clock () edge to properly clock in the first bit. When is low, data is clocked into the internal shift register via the serial-data input pin (IN) on s rising edge. The maximum guaranteed clock frequency is 1MHz. ata is latched into the input/ac register on s rising edge. IN Figure 2. Connectio for Microwire IN Figure 3. Connectio for SPI/QSPI SK SO I/O MOSI SCK I/O MICROWIRE PORT +5 SS SPI/QSPI PORT CPOL =, CPHA = MSB...LSB Control Bits C2 C1 C 3 Control Bits Figure 4. Serial-ata Format 16 Bits of Serial ata ata Bits MSB...LSB ata Bits 1

11 Low-Power, 13-Bit oltage-output ACs Table 1. Serial-Interface Programming Commands C2 C1 C X X 1 X X = on t care 16-BIT SERIAL WOR MSB LSB 13 bits of data 13 bits of data XXXXXXXXXXXXX XXXXXXXXXXXXX XXXXXXXXXXXXX Shutdown No operation (NOP) FUNCTION Load input register; AC register immediately updated (also exit shutdown). Load input register; AC register unchanged. Update AC register from input register (also exit shutdown; recall previous state) COMMAN EXECUTE IN C2 C1 C Figure 5. Serial-Interface Timing iagram t W t O t S t CL t CH t CP t H t 1 t S th IN Figure 6. etailed Serial-Interface Timing iagram 11

12 Low-Power, 13-Bit oltage-output ACs IN TO OTHER SERIAL EICES IN IN IN Figure 7. Multiple s Sharing Common IN and Lines Figure 7 shows a method of connecting several s. In this configuration, the clock and the data bus are common to all devices and separate chip-select lines are used for each IC. Applicatio Information Unipolar Output For a unipolar output, the output voltage and the reference input have the same polarity. Figure 8 shows the unipolar output circuit, which is also the typical operating circuit. Table 2 lists the unipolar output codes. For rail-to-rail output, see Figure 9. This circuit shows the with the output amplifier configured with a closed-loop gain of +2 to provide to 5 full-scale range when a 2.5 reference is used. When using the with a 1.25 reference, this circuit provides a to 2.5 full-scale range. Bipolar Output The output can be configured for bipolar operation using Figure 1 s circuit. = REF [(2NB / 8192) - 1] where NB is the numeric value of the AC s binary input code. Table 3 shows digital codes (offset binary) and the corresponding output voltage for Figure 1 s circuit. Table 2. Unipolar Code Table AC CONTENTS MSB LSB ANALOG PUT REF REF REF = + REF REF REF 8192 Using an AC Reference In applicatio where the reference has AC-signal components, the have multiplying capability within the reference input range specificatio. Figure 11 shows a technique for applying a sine-wave signal to the reference input where the AC signal is offset before being applied to REF. The reference voltage must never be more negative than GN. 12

13 Low-Power, 13-Bit oltage-output ACs Table 3. Bipolar Code Table AC CONTENTS MSB LSB ANALOG PUT REF REF REF REF REF = -REF 496 The s total harmonic distortion plus noise (TH + N) is typically less than -77dB (full-scale code), and the s TH + N is typically less than -72dB (full-scale code), given a 1p-p signal swing and input frequencies up to 25kHz. The typical -3dB frequency is 65kHz for both devices, as shown in the Typical Operating Characteristics graphs. igitally Programmable Current Source The circuit of Figure 12 places an NPN traistor (2N394 or similar) within the op-amp feedback loop to implement a digitally programmable, unidirectional current source. This circuit can be used to drive 42mA current loops, which are commonly used in industrialcontrol applicatio. The output current is calculated with the following equation: I = (REF / R) x (NB / 8192) where NB is the numeric value of the AC s binary input code and R is the see resistor shown in Figure 12. REF +5/+3.3 REF +5/+3.3 FB FB 1k AC AC 1k GN GN Figure 8. Unipolar Output Circuit Figure 9. Unipolar Rail-to-Rail Output Circuit 13

14 Low-Power, 13-Bit oltage-output ACs REF AC R1 R2 +5/ FB - R1 = R2 = 1kΩ ±.1% GN +5/ +3.3 AC REFERENCE INPUT 5mp-p 26k 1k +5/+3.3 AC 495 REF GN Figure 1. Bipolar Output Circuit Figure 11. AC Reference Input Circuit +5/ +3.3 REF AC L I 2N394 Grounding and Layout Coideratio igital or AC traient signals on GN can create noise at the analog output. Tie GN to the highest-quality ground available. Good printed circuit board ground layout minimizes crosstalk between the AC output, reference input, and digital input. Reduce crosstalk by keeping analog lines away from digital lines. Wire-wrapped boards are not recommended. FB GN R Figure 12. igitally Programmable Current Source Power-Supply Coideratio On power-up, the input and AC registers are cleared (set to zero code). For rated performance, REF should be at least 1.4 below. Bypass with a 4.7µF capacitor in parallel with a.1µf capacitor to GN. Use short lead lengths and place the bypass capacitors as close to the supply pi as possible. 14

15 Low-Power, 13-Bit oltage-output ACs _Ordering Information (continued) PART TEMP. RANGE PIN-PACKAGE INL (LSB) AEPA -4 C to +85 C 8 Plastic IP ±1/2 BEPA -4 C to +85 C 8 Plastic IP ±1 AEUA BEUA -4 C to +85 C -4 C to +85 C 8 µ 8 µ ±1/2 ±1 BMJA -55 C to +125 C 8 CERIP** ±2 ACPA C to +7 C 8 Plastic IP ±1 BCPA C to +7 C 8 Plastic IP ±2 ACUA BCUA C to +7 C C to +7 C 8 µ 8 µ ±1 ±2 BC/ C to +7 C ice* ±2 AEPA -4 C to +85 C 8 Plastic IP ±1 BEPA -4 C to +85 C 8 Plastic IP ±2 AEUA BEUA -4 C to +85 C -4 C to +85 C 8 µ 8 µ ±1 ±2 BMJA -55 C to +125 C 8 CERIP** ±4 Contact factory for availability. * ice are tested at +25 C, C parameters only. **Contact factory for availability and processing to MIL-ST-883. Chip Information TRANSISTOR COUNT: 1677 Package Information A L A2 A1 1 e B B1 A3 E E1-15 C ea eb Plastic IP PLASTIC UAL-IN-LINE PACKAGE (.3 in.) PKG. P P P P P N IM A A1 A2 A3 B B1 C 1 E E1 e ea eb L IM PINS INCHES INCHES MILLIMETERS MILLIMETERS A 15

16 Low-Power, 13-Bit oltage-output ACs Package Information (continued) e B E A A1 H.11mm.4 in C L α IM A A1 B C E e H L α INCHES MILLIMETERS PIN µ MICRO SMALL-LINE PACKAGE A L Q e B B1 L1 E1 E -15 C IM A B B1 C E E1 e L L1 Q S S INCHES MILLIMETERS S1 S CERIP CERAMIC UAL-IN-LINE PACKAGE (.3 in.) IM PINS INCHES MILLIMETERS A Maxim cannot assume respoibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licees are implied. Maxim reserves the right to change the circuitry and specificatio without notice at any time. 16 Maxim Integrated Products, 12 San Gabriel rive, Sunnyvale, CA 9486 (48) Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.