19-1559; Rev 0; 10/99 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface The MAX5302 combines a low-power, voltage-output, 12-bit digital-to-analog converter (DAC) and a precision output amplifier in an 8-pin µMAX package. It operates from a single +5V supply, drawing less than 280µA of supply current. The output amplifier’s inverting input is available to the user, allowing specific gain configurations, remote sensing, and high output current capability. This makes the MAX5302 ideal for a wide range of applications, including industrial process control. Other features include a software shutdown and power-on reset. Features ♦ 12-Bit DAC with Configurable Output Amplifier ♦ +5V Single-Supply Operation ♦ Low Supply Current: 0.28mA Normal Operation 2µA Shutdown Mode ♦ Available in 8-Pin µMAX ♦ Power-On Reset Clears DAC Output to Zero ♦ SPI/QSPI/MICROWIRE Compatible ♦ Schmitt-Trigger Digital Inputs for Direct Optocoupler Interface The serial interface is SPI™/QSPI™/MICROWIRE™ compatible. The DAC has a double-buffered input, organized as an input register followed by a DAC register. A 16-bit serial word loads data into the input register. The DAC register can be updated independently or simultaneously with the input register. All logic inputs are TTL/CMOSlogic compatible and buffered with Schmitt triggers to allow direct interfacing to optocouplers. Applications Industrial Process Control Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX5302CUA 0°C to +70°C 8 µMAX MAX5302EUA -40°C to +85°C 8 µMAX Automatic Test Equipment Digital Offset and Gain Adjustment Motion Control Remote Industrial Control Microprocessor-Controlled Systems Functional Diagram VDD GND Pin Configuration TOP VIEW REF FB DAC REGISTER OUT DAC CONTROL DIN SCLK 8 VDD 7 GND DIN 3 6 REF SCLK 4 5 FB CS 2 INPUT REGISTER CS OUT 1 16-BIT SHIFT REGISTER MAX5302 MAX5302 µMAX SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX5302 __________________General Description MAX5302 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface ABSOLUTE MAXIMUM RATINGS VDD to GND ..............................................................-0.3V to +6V REF, OUT, FB to GND ................................-0.3V to (VDD + 0.3V) Digital Inputs to GND ...............................................-0.3V to +6V Continuous Current into Any Pin.......................................±20mA Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.10mW/°C above +70°C) .........330mW Operating Temperature Ranges MAX5302CUA ...................................................0°C to +70°C MAX5302EUA ................................................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C 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 conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Circuit of Figure 8, VDD = +5V ±10%, VREF = +2.5V, RL = 5kΩ, CL = 100pF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C. Output buffer connected in unity-gain configuration.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS STATIC PERFORMANCE—ANALOG SECTION Resolution N Bits 12 Differential Nonlinearity DNL Integral Nonlinearity (Note 1) INL Offset Error VOS ±0.3 TCVOS 6 GE -0.3 Offset-Error Tempco Gain Error (Note 1) Guaranteed monotonic Gain-Error Tempco Power-Supply Rejection Ratio ±1.0 LSB ±4 LSB ±8 ±3 1 PSRR 4.5V ≤ VDD ≤ 5.5V mV ppm/°C LSB ppm/°C 800 µV/V REFERENCE INPUT Reference Input Range VREF Reference Input Resistance RREF 0 Code dependent, minimum at code 1554 hex 14 VDD - 1.4 V 20 kΩ MULTIPLYING-MODE PERFORMANCE Reference -3dB Bandwidth VREF = 0.67Vp-p 650 kHz Reference Feedthrough Input code = all 0s, VREF = 3.6Vp-p at 1kHz -84 dB VREF = 1Vp-p at 25kHz, code = full scale 77 dB Signal-to-Noise Plus Distortion Ratio SINAD DIGITAL INPUTS Input Voltage High VIH Input Voltage Low VIL Input Leakage Current IIN Input Capacitance CIN 2 V 2.4 VIN = 0 or VDD 0.001 8 _______________________________________________________________________________________ 0.8 V ±0.5 µA pF Low-Power, 12-Bit Voltage-Output DAC with Serial Interface (Circuit of Figure 8, VDD = +5V ±10%, VREF = +2.5V, RL = 5kΩ, CL = 100pF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C. Output buffer connected in unity-gain configuration.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DIGITAL INPUTS DYNAMIC PERFORMANCE Voltage Output Slew Rate SR Output Settling Time To ±1/2LSB, VSTEP = 2.5V Output Voltage Swing Rail-to-rail (Note 2) 0.6 V/µs 14 µs 0 to VDD Current into FB 0.001 Start-Up Time CS = VDD, DIN = 100kHz Digital Feedthrough V ±0.1 µA 20 µs 5 nVs POWER SUPPLIES Supply Voltage VDD Supply Current IDD Supply Current in Shutdown 4.5 5.5 V (Note 3) 0.28 0.4 mA (Note 3) 4 20 µA 0.001 ±0.5 µA Reference Current in Shutdown TIMING CHARACTERISTICS (Figure 6) SCLK Clock Period tCP 100 ns SCLK Pulse Width High tCH 40 ns SCLK Pulse Width Low tCL 40 ns CS Fall to SCLK Rise Setup Time tCSS 40 ns SCLK Rise to CS Rise Hold Time tCSH 0 ns DIN Setup Time tDS 40 ns DIN Hold Time tDH 0 ns SCLK Rise to CS Fall Delay tCS0 40 ns CS Rise to SCLK Rise Hold Time tCS1 40 ns CS Pulse Width High tCSW 100 ns Note 1: Guaranteed from code 11 to code 4095 in unity-gain configuration. Note 2: Accuracy is better than 1LSB for VOUT = 8mV to (VDD - 100mV), guaranteed by a power-supply rejection test at the end points. Note 3: RL = ∞, digital inputs at GND or VDD. _______________________________________________________________________________________ 3 MAX5302 ELECTRICAL CHARACTERISTICS (continued) __________________________________________Typical Operating Characteristics (VDD = +5V, RL = 5kΩ, CL = 100pF, TA = +25°C, unless otherwise noted.) -4 RELATIVE OUTPUT (dB) 0.1 -0.1 -0.2 -0.3 -8 -12 360 -16 320 300 280 260 220 -20 0.4 1.2 2.0 2.8 3.6 REFERENCE VOLTAGE (V) 4.4 0 2M 2.5M 4 3 300 250 200 150 100 1 50 60 100 OUTPUT FFT PLOT -60 -80 5.6 1.6 2.7 3.8 FREQUENCY (kHz) 4.9 6.0 100 10 FREQUENCY (kHz) FULL-SCALE OUTPUT vs. LOAD REFERENCE FEEDTHROUGH AT 1kHz 0 MAX5302 toc08 2.49972 2.49968 2.49964 2.49956 0.1k 1 SUPPLY VOLTAGE (V) REFERENCE INPUT SIGNAL -20 -40 -60 OUTPUT FEEDTHROUGH -80 2.49960 -100 -75 6.0 SIGNAL AMPLITUDE (dB) -40 5.2 2.49976 FULL-SCALE OUTPUT (V) -20 4.8 2.49980 MAX5302 toc07 VREF = 3.6Vp-p CODE = FULL SCALE fIN = 1kHz -70 -90 4.4 TEMPERATURE (°C) 0 -65 -85 4.0 140 140 -80 0 20 100 -60 350 2 60 VREF = 2.5VDC + 1Vp-p SINE CODE = FULL SCALE -55 THD + NOISE (dB) SUPPLY CURRENT (µA) 5 20 -50 MAX5302 toc05 400 6 -20 -20 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY 450 7 0.5 200 -60 3M TEMPERATURE (°C) 500 8 0 -60 1.5M SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX5302 toc04 9 1M FREQUENCY (Hz) POWER-DOWN SUPPLY CURRENT vs. TEMPERATURE 10 500k MAX5302 toc06 -0.5 POWER-DOWN SUPPLY CURRENT (µA) 340 240 -0.4 4 RL = ∞ 380 MAX5302-09a/09b INL (LSB) 0 400 SUPPLY CURRENT (µA) 0.2 MAX5302 toc02 0 MAX5302 toc01 0.3 SUPPLY CURRENT vs. TEMPERATURE MAX5302 toc03 REFERENCE VOLTAGE INPUT FREQUENCY RESPONSE INTEGRAL NONLINEARITY vs. REFERENCE VOLTAGE SIGNAL AMPLITUDE (dB) MAX5302 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface -100 1k 10k LOAD (Ω) 100k 1M 0.5 1.6 2.7 3.8 FREQUENCY (kHz) _______________________________________________________________________________________ 4.9 6.0 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface DIGITAL FEEDTHROUGH (fSCLK = 100kHz) MAX5302 toc11 MAX5302 toc10 MAJOR-CARRY TRANSITION CS 5V/div SCLK 2V/div OUT AC-COUPLED 100mV/div OUT AC-COUPLED 10mV/div CODE = 2048 10µs/div 2µs/div CS = 5V MAX5302 toc12 DYNAMIC RESPONSE OUT 1V/div GND 10µs/div GAIN = 2, SWITCHING FROM CODE 0 TO 4020 _______________________________________________________________________________________ 5 MAX5302 Typical Operating Characteristics (continued) (VDD = +5V, RL = 5kΩ, CL = 100pF, TA = +25°C, unless otherwise noted.) MAX5302 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface _____________________Pin Description PIN NAME 1 OUT 2 CS Chip-Select Input. Active low. 3 DIN Serial-Data Input 4 SCLK Serial-Clock Input 5 FB 6 REF Reference Voltage Input 7 GND Ground 8 VDD Positive Power Supply FB FUNCTION R DAC Output Amplifier Feedback OUT R 2R 2R 2R 2R 2R MSB REF AGND SHOWN FOR ALL 1s ON DAC Detailed Description The MAX5302 contains a voltage-output digital-to-analog converter (DAC) that is easily addressed using a simple 3-wire serial interface. The IC includes a 16-bit shift register, and has a double-buffered input composed of an input register and a DAC register (see Functional Diagram). In addition to the voltage output, the amplifier’s negative input is available to the user. The DAC is an inverted R-2R ladder network that converts a digital input (12 data bits plus 1 sub-bit) into an equivalent analog output voltage in proportion to the applied reference voltage. Figure 1 shows a simplified circuit diagram of the DAC. Reference Inputs The reference input accepts positive DC and AC signals. The voltage at the reference input sets the full-scale output voltage for the DAC. The reference input voltage range is 0 to (VDD - 1.4V). The output voltage (VOUT) is represented by a digitally programmable voltage source, as expressed in the following equation: VOUT = (VREF · NB / 4096) Gain where NB is the numeric value of the DAC’s binary input code (0 to 4095), VREF 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 DAC has an input code of 1554 hex, to a high value exceeding several gigaohms (leakage currents) with an input code of 0000 hex. Because the input impedance at the reference pin is code dependent, load regulation of the reference source is important. 6 R DAC Output Voltage Figure 1. Simplified DAC Circuit Diagram In shutdown mode, the MAX5302’s REF input enters a high-impedance state with a typical input leakage current of 0.001µA. The reference input capacitance is also code dependent and typically ranges from 15pF (with an input code of all 0s) to 50pF (at full scale). The MAX873 +2.5V reference is recommended for the MAX5302. Output Amplifier The MAX5302’s DAC output is internally buffered by a precision amplifier with a typical slew rate of 0.6V/µs. Access to the output amplifier’s inverting input provides the user greater flexibility in output gain setting/signal conditioning (see the Applications Information section). With a full-scale transition at the MAX5302 output, the typical settling time to ±1/2LSB is 14µs when loaded with 5kΩ in parallel with 100pF (loads less than 2kΩ degrade performance). The amplifier’s output dynamic responses and settling performances are shown in the Typical Operating Characteristics. Shutdown Mode The MAX5302 features a software-programmable shutdown that reduces supply current to a typical value of 4µA. Writing 111X XXXX XXXX XXXX as the input control word puts the device in shutdown mode (Table 1). In shutdown mode, the amplifier’s output and the reference input enter a high-impedance state. The serial interface remains active. Data in the input registers is retained in shutdown, allowing the MAX5302 to recall the output state prior to entering shutdown. Exit shutdown mode by either recalling the previous configuration or _______________________________________________________________________________________ Low-Power, 12-Bit Voltage-Output DAC with Serial Interface SCLK MAX5302 SK Serial-Interface Configurations DIN SO CS I/O The MAX5302’s 3-wire serial interface is compatible with both MICROWIRE (Figure 2) and SPI/QSPI (Figure 3). The serial-input word consists of 3 control bits followed by 12+1 data bits (MSB first), as shown in Figure 4. The 3-bit control code determines the MAX5302’s response outlined in Table 1. MICROWIRE PORT The MAX5302’s digital inputs are double buffered. Depending on the command issued through the serial interface, the input register can be loaded without affecting the DAC register, the DAC register can be loaded directly, or the DAC register can be updated from the input register (Table 1). Figure 2. Connections for MICROWIRE Serial-Interface Description +5V The MAX5302 requires 16 bits of serial data. Table 1 lists the serial-interface programming commands. For certain commands, the 12+1 data bits are “don’t cares.” Data is sent MSB first and can be sent in two 8-bit packets or one 16-bit word (CS must remain low until 16 bits are transferred). The serial data is composed of 3 control SS DIN MAX5302 MOSI SCLK SCK CS SPI/QSPI PORT MSB ..................................................................................LSB 16 Bits of Serial Data Control Bits I/O C2 C1 Data Bits MSB ................................LSB Sub-Bit C0 D11 .....................................D0, S0 3 Control Bits CPOL = 0, CPHA = 0 12+1 Data Bits Figure 4. Serial-Data Format Figure 3. Connections for SPI/QSPI Table 1. Serial-Interface Programming Commands 16-BIT SERIAL WORD S0 FUNCTION C2 C1 C0 D11...............D0 MSB LSB S0 X 0 0 12 bits of data 0 Load input register; DAC register immediately updated (also exit shutdown). X 0 1 12 bits of data 0 Load input register; DAC register unchanged. X 1 0 XXXXXXXXXXXX X Update DAC register from input register (also exit shutdown; recall previous state). 1 1 1 XXXXXXXXXXXX X Shutdown 0 1 1 XXXXXXXXXXXX X No operation (NOP) X = Don’t care _______________________________________________________________________________________ 7 MAX5302 by updating the DAC with new data. When powering up the device or bringing it out of shutdown, allow 20µs for the output to stabilize. MAX5302 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface CS COMMAND EXECUTED SCLK 1 DIN 8 C1 C2 C0 D11 D10 D9 D8 9 D7 D6 16 D5 D4 D3 D2 D1 D0 S0 Figure 5. Serial-Interface Timing Diagram tCSW CS tCSO tCSS tCL tCP tCH tCSH tCS1 SCLK tDS tDH DIN Figure 6. Detailed Serial-Interface Timing Diagram DIN SCLK CS1 CS2 TO OTHER SERIAL DEVICES CS3 CS CS MAX5302 CS MAX5302 MAX5302 SCLK SCLK SCLK DIN DIN DIN Figure 7. Multiple MAX5302s Sharing Common DIN and SCLK Lines 8 _______________________________________________________________________________________ Low-Power, 12-Bit Voltage-Output DAC with Serial Interface Applications Information Unipolar Output For a unipolar output, the output voltage and the reference input have the same polarity. Figure 8 shows the MAX5302 unipolar output circuit, which is also the typical operating circuit. Table 2 lists the unipolar output codes. Figure 9 illustrates a Rail-to-Rail® output. This circuit shows the MAX5302 with the output amplifier configured with a closed-loop gain of +2 to provide a 0V to 5V fullscale range when a 2.5V reference is used. Bipolar Output The MAX5302 output can be configured for bipolar operation using Figure 10’s circuit according to the following equation: VOUT = VREF [(2NB / 4096) - 1] where NB is the numeric value of the DAC’s binary input code. Table 3 shows digital codes (offset binary) and the corresponding output voltage for Figure 10’s circuit. Using an AC Reference In applications where the reference has AC-signal components, the MAX5302 has multiplying capability within the reference input range specifications. 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 GND. The MAX5302’s total harmonic distortion plus noise (THD+N) is typically less than -77dB (full-scale code), given a 1Vp-p signal swing and input frequencies up to 25kHz. The typical -3dB frequency is 650kHz, as shown in the Typical Operating Characteristics graphs. Table 2. Unipolar Code Table DAC CONTENTS MSB LSB +5V REF VDD FB MAX5302 1111 1111 1111 (0) 4095 +VREF 4096 1000 0000 0001 (0) 2049 +VREF 4096 1000 0000 0000 (0) + VREF 2048 +VREF = 4096 2 0111 1111 1111 (0) 2047 +VREF 4096 0000 0000 0001 (0) 1 +VREF 4096 0000 0000 0000 (0) 0V DAC OUT GND Figure 8. Unipolar Output Circuit ANALOG OUTPUT Note: ( ) are for sub-bit. Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd. _______________________________________________________________________________________ 9 MAX5302 bits (C2, C1, C0), followed by the 12+1 data bits D11...D0, S0 (Figure 4). Set the sub-bit (S0) to zero. The 3-bit control code determines the register to be updated and the configuration when exiting shutdown. Figures 5 and 6 show the serial-interface timing requirements. The chip-select (CS) pin must be low to enable the DAC’s serial interface. When CS is high, the interface control circuitry is disabled. CS must go low at least tCSS before the rising serial-clock (SCLK) edge to properly clock in the first bit. When CS is low, data is clocked into the internal shift register through the serialdata input pin (DIN) on SCLK’s rising edge. The maximum guaranteed clock frequency is 10MHz. Data is latched into the MAX5302 input/DAC register on CS’s rising edge. Figure 7 shows a method of connecting several MAX5302s. In this configuration, the clock and the data bus are common to all devices, and separate chip-select lines are used for each IC. MAX5302 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface R1 R2 REF +5V +5V REF VDD VDD 10k FB V+ FB MAX5302 10k DAC OUT VOUT DAC OUT V- GND MAX5302 GND R1 = R2 = 10kΩ ±0.1% Figure 9. Unipolar Rail-to-Rail Output Circuit Digitally Programmable Current Source The circuit of Figure 12 places an NPN transistor (2N3904 or similar) within the op amp feedback loop to implement a digitally programmable, unidirectional current source. The output current is calculated with the following equation: Figure 10. Bipolar Output Circuit Table 3. Bipolar Code Table DAC CONTENTS MSB LSB 1 1 1 1 1 1 1 1 11 1 1 ( 0 ) 2047 +VREF 2048 1 0 0 0 0 0 0 0 00 0 1 ( 0 ) 1 +VREF 2048 1 0 0 0 0 0 0 0 00 0 0 ( 0 ) 0V IOUT = (VREF / R) (NB / 4096) where NB is the numeric value of the DAC’s binary input code, and R is the sense resistor shown in Figure 12. Power-Supply Considerations On power-up, the input and DAC registers are cleared (set to zero code). For rated MAX5302 performance, VREF must be at least 1.4V below VDD. Bypass VDD with a 4.7µF capacitor in parallel with a 0.1µF capacitor to GND. Use short lead lengths and place the bypass capacitors as close to the supply pins as possible. Grounding and Layout Considerations Digital or AC transient signals on GND can create noise at the analog output. Connect GND to the highest-quality ground available. Good PC board ground layout minimizes crosstalk between the DAC output, reference input, and digital input. Reduce crosstalk by keeping analog lines away from digital lines. Wire-wrapped boards are not recommended. 10 ANALOG OUTPUT 0 1 1 1 1 1 1 1 11 1 1 ( 0 ) 1 -VREF 2048 0 0 0 0 0 0 0 0 00 0 1 ( 0 ) 2047 -VREF 2048 0 0 0 0 0 0 0 0 00 0 0 ( 0 ) 2048 -VREF = - VREF 2048 Note: ( ) are for sub-bit. ______________________________________________________________________________________ Low-Power, 12-Bit Voltage-Output DAC with Serial Interface MAX5302 +5V AC REFERENCE INPUT +5V 26k +5V MAX495 REF VDD VL MAX5302 500mVp-p IOUT DAC 10k VDD REF OUT 2N3904 FB DAC OUT GND R MAX5302 GND Figure 11. AC Reference Input Circuit Figure 12. Digitally Programmable Current Source Chip Information TRANSISTOR COUNT: 3053 SUBSTRATE CONNECTED TO AGND ______________________________________________________________________________________ 11 Low-Power, 12-Bit Voltage-Output DAC with Serial Interface 8LUMAXD.EPS MAX5302 Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.