19-1098; Rev 1; 12/96 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface ______________________________Features ♦ Four 12-Bit DACs with Configurable Output Amplifiers Each DAC has a double-buffered input organized as an input register followed by a DAC register. A 16-bit serial word loads data into each input/DAC register. The serial interface is compatible with SPI™/QSPI™ and Microwire™. It allows the input and DAC registers to be updated independently or simultaneously with a single software command. The DAC registers can be simultaneously updated via the 3-wire serial interface. All logic inputs are TTL/CMOS-logic compatible. ________________________Applications Industrial Process Controls Automatic Test Equipment Digital Offset and Gain Adjustment Motion Control Remote Industrial Controls Microprocessor-Controlled Systems ♦ +5V Single-Supply Operation ♦ Low Supply Current: 0.85mA Normal Operation 10µA Shutdown Mode ♦ Available in 20-Pin SSOP ♦ Power-On Reset Clears all Registers and DACs to Zero ♦ Capable of Recalling Last State Prior to Shutdown ♦ SPI/QSPI and Microwire Compatible ♦ Simultaneous or Independent Control of DACs via 3-Wire Serial Interface ♦ User-Programmable Digital Output _________________Ordering Information PIN-PACKAGE INL (LSB) 0°C to +70°C 20 Plastic DIP ±1/2 PART TEMP. RANGE MAX525ACPP MAX525BCPP 0°C to +70°C 20 Plastic DIP ±1 MAX525ACAP 0°C to +70°C 20 SSOP ±1/2 MAX525BCAP 0°C to +70°C 20 SSOP ±1 Ordering Information continued on last page. Pin Configuration appears at end of data sheet. _________________________________________________________________________Functional Diagram DOUT CL PDL DGND AGND SR CONTROL LOGIC OUTPUT CS DIN SCLK UPO REFAB FBA DECODE CONTROL 16-BIT SHIFT REGISTER VDD MAX525 OUTA INPUT REGISTER A DAC REGISTER A DAC A INPUT REGISTER B DAC REGISTER B DAC B INPUT REGISTER C DAC REGISTER C DAC C INPUT REGISTER D DAC REGISTER D DAC D FBB OUTB FBC OUTC FBD OUTD REFCD 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 408-737-7600 ext. 3468. MAX525 __________________General Description The MAX525 combines four low-power, voltage-output, 12-bit digital-to-analog converters (DACs) and four precision output amplifiers in a space-saving, 20-pin package. In addition to the four voltage outputs, each amplifier’s negative input is also available to the user. This facilitates specific gain configurations, remote sensing, and high output drive capacity, making the MAX525 ideal for industrial-process-control applications. Other features include software shutdown, hardware shutdown lockout, an active-low reset which clears all registers and DACs to zero, a user-programmable logic output, and a serial-data output. MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface ABSOLUTE MAXIMUM RATINGS VDD to AGND............................................................-0.3V to +6V VDD to DGND ...........................................................-0.3V to +6V AGND to DGND ..................................................................±0.3V REFAB, REFCD to AGND ...........................-0.3V to (VDD + 0.3V) OUT_, FB_ to AGND...................................-0.3V to (VDD + 0.3V) Digital Inputs to DGND.............................................-0.3V to +6V DOUT, UPO to DGND ................................-0.3V to (VDD + 0.3V) Continuous Current into Any Pin.......................................±20mA Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 8.00mW/°C above +70°C) .................640mW SSOP (derate 8.00mW/°C above +70°C) ......................640mW CERDIP (derate 11.11mW/°C above +70°C) .................889mW Operating Temperature Ranges MAX525_C_P ........................................................0°C to +70°C MAX525_E_P .....................................................-40°C to +85°C MAX525_MJP ..................................................-55°C to +125°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 (VDD = +5V ±10%, AGND = DGND = 0V, REFAB = REFCD = 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 (Figure 9).) PARAMETER SYMBOL CONDITIONS MIN TYP MAX ±0.25 ±0.5 UNITS STATIC PERFORMANCE—ANALOG SECTION Resolution N Integral Nonlinearity (Note 1) INL Differential Nonlinearity DNL Offset Error VOS 12 MAX525A ±1.0 Guaranteed monotonic ±1.0 LSB ±6.0 mV 6 GE ppm/°C -0.8 Gain-Error Tempco Power-Supply Rejection Ratio ±2.0 1 PSRR LSB MAX525B Offset-Error Tempco Gain Error (Note 1) Bits 4.5V ≤ VDD ≤ 5.5V LSB ppm/°C 100 600 µV/V MATCHING PERFORMANCE (TA = +25°C) Gain Error GE Offset Error Integral Nonlinearity INL -0.8 ±2.0 LSB ±1.0 ±6.0 mV ±0.35 ±1.0 LSB REFERENCE INPUT Reference Input Range VREF Reference Input Resistance RREF Reference Current in Shutdown 2 0 Code-dependent, minimum at code 555 hex VDD - 1.4 10 V kΩ 0.01 _______________________________________________________________________________________ ±1 µA Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface (VDD = +5V ±10%, AGND = DGND = 0V, REFAB = REFCD = 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 (Figure 9).) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 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 72 dB Signal-to-Noise Plus Distortion Ratio SINAD DIGITAL INPUTS Input High Voltage VIH Input Low Voltage VIL Input Leakage Current IIN Input Capacitance CIN 2.4 VIN = 0V or VDD V 0.01 0.8 V ±1.0 µA 8 pF DIGITAL OUTPUTS Output High Voltage VOH ISOURCE = 2mA Output Low Voltage VOL ISINK = 2mA VDD - 0.5 V 0.13 0.4 V DYNAMIC PERFORMANCE Voltage Output Slew Rate SR Output Settling Time To ±1/2LSB, VSTEP = 2.5V Output Voltage Swing Rail to rail (Note 2) RL = ∞ Start-Up Time Exiting Shutdown Mode CS = VDD, DIN = 100kHz Digital Feedthrough V/µs 12 µs 0 to VDD Current into FB_ OUT_ Leakage Current in Shutdown 0.6 Digital Crosstalk V 0 0.1 µA 0.01 ±1 µA 15 µs 5 nV-s 5 nV-s POWER SUPPLIES Supply Voltage VDD Supply Current IDD Supply Current in Shutdown Reference Current in Shutdown 4.5 (Note 3) (Note 3) 5.5 V 0.98 mA 10 20 µA 0.01 ±1 µA 0.85 Note 1: Guaranteed from code 11 to code 4095 in unity-gain configuration. Note 2: Accuracy is better than 1.0LSB for VOUT = 6mV to VDD - 60mV, guaranteed by PSR test on end points. Note 3: RL = ∞, digital inputs at DGND or VDD. _______________________________________________________________________________________ 3 MAX525 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VDD = +5V ±10%, AGND = DGND = 0V, REFAB = REFCD = 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 (Figure 9).) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 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 DOUT Valid Propagation Delay tD01 CLOAD = 200pF 80 ns SCLK Fall to DOUT Valid Propagation Delay tD02 CLOAD = 200pF 70 80 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 __________________________________________Typical Operating Characteristics (VDD = +5V, TA = +25°C, unless otherwise noted.) INTEGRAL NONLINEARITY vs. REFERENCE VOLTAGE -4 RELATIVE OUTPUT (dB) 0.1 0 -0.1 -0.2 -0.3 -8 -12 -16 4 850 800 750 700 650 600 550 RL = 5kΩ -20 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 REFERENCE VOLTAGE (V) 950 900 -0.4 -0.5 1000 0 500k 1M 1.5M 2M FREQUENCY (Hz) 2.5M MAX525-03 REFAB SWEPT 0.67Vp-p RL = 5kΩ CL = 100pF SUPPLY CURRENT (µA) 0 MAX525-02 0.2 SUPPLY CURRENT vs. TEMPERATURE REFERENCE VOLTAGE INPUT FREQUENCY RESPONSE MAX525-01 0.3 INL (LSB) MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface 3M CODE = FFF hex 500 -55 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) _______________________________________________________________________________________ Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY DAC CODE = ALL 1s REFAB = 1Vp-p RL = 5kΩ CL = 100pF 0.45 THD + NOISE (%) 900 850 800 750 0.35 0.30 0.25 0.20 0.15 700 4.6 4.8 5.0 5.2 5.4 100 10 1 5.6 0 REFAB INPUT SIGNAL SIGNAL AMPLITUDE (dB) -1 -2 -3 -4 -20 -5 1 LOAD (kΩ) 10 4.9 6.0 VREF = 3.6Vp-p @ 1kHz RL = 5kΩ CL = 100pF -40 -60 OUTA FEEDTHROUGH -80 0.1 3.8 REFERENCE FEEDTHROUGH AT 1kHz MAX525-09 0 2.7 FREQUENCY (kHz) FULL-SCALE ERROR vs. LOAD 0.01 1.6 FREQUENCY (kHz) SUPPLY VOLTAGE (V) 100 MAX525-11 4.4 -60 -100 0.5 0 4.2 -40 0.05 CODE = FFF hex 600 4.0 VREF = 1kHz, 0.006V TO 3.6V RL = 5kΩ CL = 100pF -20 -80 0.10 650 FULL-SCALE ERROR (LSB) SUPPLY CURRENT (µA) 0.40 SIGNAL AMPLITUDE (dB) 950 OUTPUT FFT PLOT 0 MAX525-05 0.50 MAX525-04 1000 MAX525-10 SUPPLY CURRENT vs. SUPPLY VOLTAGE -100 0.5 1.2 1.9 2.6 3.3 4.0 FREQUENCY (kHz) _______________________________________________________________________________________ 5 MAX525 ____________________________Typical Operating Characteristics (continued) (VDD = +5V, TA = +25°C, unless otherwise noted.) ____________________________Typical Operating Characteristics (continued) (VDD = +5V, TA = +25°C, unless otherwise noted.) MAJOR-CARRY TRANSITION MAX525-08 MAX525-07 DIGITAL FEEDTHROUGH (SCLK = 100kHz) CS 5V/div SCLK, 2V/div OUTB, AC COUPLED 100mV/div OUTA, AC COUPLED 10mV/div 10µs/div 2µs/div VREF = 2.5V, RL = 5kΩ, CL = 100pF VREF = 2.5V, RL = 5kΩ, CL = 100pF CS = PDL = CL = 5V, DIN = 0V DAC A CODE SET TO 800 hex ANALOG CROSSTALK MAX525-13 DYNAMIC RESPONSE MAX525-12 MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface OUTA, 1V/div OUTA, 1V/div GND OUTB, AC COUPLED 10mV/div 10µs/div VREF = 2.5V, RL = 5kΩ, CL = 100pF DAC A CODE SWITCHING FROM 00B hex TO FFF hex DAC B CODE SET TO 800 hex 6 10µs/div VREF = 2.5V, RL = 5kΩ, CL = 100pF SWITCHING FROM CODE 000 hex TO FB4 hex OUTPUT AMPLIFIER GAIN = +2 _______________________________________________________________________________________ Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface PIN NAME FUNCTION 1 AGND 2 FBA 3 OUTA DAC A Output Voltage 4 OUTB DAC B Output Voltage 5 FBB 6 REFAB 7 CL Clear All DACs and Registers. Resets all outputs (OUT_, UPO, DOUT) to 0, active low. 8 CS Chip-Select Input. Active low. 9 DIN Serial-Data Input 10 SCLK Serial Clock Input 11 DGND Digital Ground 12 DOUT Serial-Data Output 13 UPO User-Programmable Logic Output 14 PDL Power-Down Lockout. Active low. Locks out software shutdown if low. 15 REFCD 16 FBC 17 OUTC DAC C Output Voltage 18 OUTD DAC D Output Voltage 19 FBD DAC D Output Amplifier Feedback 20 VDD Positive Power Supply Analog Ground DAC A Output Amplifier Feedback DAC B Output Amplifier Feedback Reference Voltage Input for DAC A and DAC B Reference Voltage Input for DAC C and DAC D DAC C Output Amplifier Feedback _______________________________________________________________________________________ 7 MAX525 ______________________________________________________________Pin Description MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface FB_ R 2R 2R D0 R 2R D9 OUT_ R 2R 2R D10 D11 REF_ AGND SHOWN FOR ALL 1s ON DAC Figure 1. Simplified DAC Circuit Diagram _______________Detailed Description The MAX525 contains four 12-bit, voltage-output digital-to-analog converters (DACs) that are easily addressed using a simple 3-wire serial interface. It includes a 16-bit data-in/data-out shift register, and each DAC has a doubled-buffered input composed of an input register and a DAC register (see Functional Diagram). In addition to the four voltage outputs, each amplifier’s negative input is available to the user. The DACs are inverted R-2R ladder networks that convert 12-bit digital inputs into equivalent analog output voltages in proportion to the applied reference voltage inputs. DACs A and B share the REFAB reference input, while DACs C and D share the REFCD reference input. The two reference inputs allow different full-scale output voltage ranges for each pair of DACs. Figure 1 shows a simplified circuit diagram of one of the four DACs. Reference Inputs The two reference inputs accept positive DC and AC signals. The voltage at each reference input sets the full-scale output voltage for its two corresponding DACs. The reference input voltage range is 0V to (VDD - 1.4V). The output voltages (VOUT_) are represented by a digitally programmable voltage source as: VOUT_ = (VREF x NB / 4096) x 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. 8 The impedance at each reference input is code-dependent, ranging from a low value of 10kΩ when both DACs connected to the reference have an input code of 555 hex, to a high value exceeding several gigohms (leakage currents) with an input code of 000 hex. Because the input impedance at the reference pins is code-dependent, load regulation of the reference source is important. The REFAB and REFCD reference inputs have a 10kΩ guaranteed minimum input impedance. When the two reference inputs are driven from the same source, the effective minimum impedance is 5kΩ. A voltage reference with a load regulation of 6ppm/mA, such as the MAX873, would typically deviate by 0.025LSB (0.061LSB worst case) when driving both MAX525 reference inputs simultaneously at 2.5V. Driving the REFAB and REFCD pins separately improves reference accuracy. In shutdown mode, the MAX525’s REFAB and REFCD inputs enter a high-impedance state with a typical input leakage current of 0.01µA. The reference input capacitance is also code dependent and typically ranges from 20pF with an input code of all 0s to 100pF with an input code of all 1s. Output Amplifiers All MAX525 DAC outputs are internally buffered by precision amplifiers with a typical slew rate of 0.6V/µs. Access to the inverting input of each output amplifier provides the user greater flexibility in output gain setting/ signal conditioning (see the Applications Information section). With a full-scale transition at the MAX525 output, the typical settling time to ±1/2LSB is 12µs when loaded with 5kΩ in parallel with 100pF (loads less than 2kΩ degrade performance). The MAX525 output amplifier’s output dynamic responses and settling performances are shown in the Typical Operating Characteristics. Power-Down Mode The MAX525 features a software-programmable shutdown that reduces supply current to a typical value of 10µA. The power-down lockout (PDL) pin must be high to enable the shutdown mode. Writing 1100XXXXXXXXXXXX as the input-control word puts the MAX525 in powerdown mode (Table 1). _______________________________________________________________________________________ Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface MAX525 SCLK SK DIN SO DOUT* SI* CS I/O Serial-Interface Configurations The MAX525’s 3-wire serial interface is compatible with both Microwire™ (Figure 2) and SPI™/QSPI™ (Figure 3). The serial input word consists of two address bits and two control bits followed by 12 data bits (MSB first), as shown in Figure 4. The 4-bit address/ control code determines the MAX525’s response outlined in Table 1. The connection between DOUT and the serial-interface port is not necessary, but may be used for data echo. Data held in the MAX525’s shift register can be shifted out of DOUT and returned to the microprocessor (µP) for data verification. The MAX525’s digital inputs are double buffered. Depending on the command issued through the serial interface, the input register(s) can be loaded without affecting the DAC register(s), the DAC register(s) can be loaded directly, or all four DAC registers can be updated simultaneously from the input registers (Table 1). MICROWIRE PORT *THE DOUT-SI CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX525, BUT MAY BE USED FOR READBACK PURPOSES. Figure 2. Connections for Microwire +5V DOUT* DIN MAX525 SS MISO* MOSI SCLK SCK Serial-Interface Description The MAX525 requires 16 bits of serial data. Table 1 lists the serial-interface programming commands. For certain commands, the 12 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 two DAC address bits (A1, A0) and two control bits (C1, C0), followed by the 12 data bits D11…D0 (Figure 4). The 4-bit address/control code determines: • The register(s) to be updated • The clock edge on which data is to be clocked out via the serial-data output (DOUT) • The state of the user-programmable logic output (UPO) • If the part is to go into shutdown mode (assuming PDL is high) • How the part is configured when coming out of shutdown mode. MAX525 In power-down mode, the MAX525 output amplifiers and the reference inputs enter a high-impedance state. The serial interface remains active. Data in the input registers is retained in power-down, allowing the MAX525 to recall the output states prior to entering shutdown. Start up from power-down either by recalling the previous configuration or by updating the DACs with new data. When powering up the device or bringing it out of shutdown, allow 15µs for the outputs to stabilize. CS SPI/QSPI PORT I/O CPOL = 0, CPHA = 0 *THE DOUT-MISO CONNECTION IS NOT REQUIRED FOR WRITING TO THE MAX525, BUT MAY BE USED FOR READBACK PURPOSES. Figure 3. Connections for SPI/QSPI MSB ..................................................................................LSB 16 Bits of Serial Data Address Bits A1 A0 Control Bits C1 C0 Data Bits MSB.............................................LSB D11................................................D0 4 Address/ Control Bits 12 Data Bits Figure 4. Serial-Data Format _______________________________________________________________________________________ 9 MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface Table 1. Serial-Interface Programming Commands C1 A1 16-BIT C0SERIAL WORD A0 C1 C0 D11.................D0 MSB LSB FUNCTION 0 0 1 1 0 1 0 1 0 0 0 0 1 1 1 1 12-bit DAC data 12-bit DAC data 12-bit DAC data 12-bit DAC data Load input register A; DAC registers unchanged. Load input register B; DAC registers unchanged. Load input register C; DAC registers unchanged. Load input register D; DAC registers unchanged. 0 0 1 1 0 1 0 1 1 1 1 1 1 1 1 1 12-bit DAC data 12-bit DAC data 12-bit DAC data 12-bit DAC data Load input register A; all DAC registers updated. Load input register B; all DAC registers updated. Load input register C; all DAC registers updated. Load input register D; all DAC registers updated. 0 1 0 0 XXXXXXXXXXXX Update all DAC registers from their respective input registers (start-up). 1 0 0 0 12-bit DAC data Load all DAC registers from shift register (start-up). 1 1 0 0 XXXXXXXXXXXX Shutdown (provided PDL = 1) 0 0 1 0 XXXXXXXXXXXX UPO goes low (default) 0 1 1 0 XXXXXXXXXXXX UPO goes high 0 0 0 0 XXXXXXXXXXXX No operation (NOP) to DAC registers 1 1 1 0 XXXXXXXXXXXX Mode 1, DOUT clocked out on SCLK’s rising edge. All DAC registers updated. 1 0 1 0 XXXXXXXXXXXX Mode 0, DOUT clocked out on SCLK’s falling edge. All DAC registers updated (default). “X” = Don’t care Figure 5 shows the serial-interface timing requirements. The chip-select pin (CS) 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 via the serial-data input pin (DIN) on SCLK’s rising edge. The maximum guaranteed clock frequency is 10MHz. Data is latched into the appropriate MAX525 input/DAC registers on CS’s rising edge. The programming command Load-All-DACs-From-ShiftRegister allows all input and DAC registers to be simultaneously loaded with the same digital code from the input shift register. The no operation (NOP) command leaves the register contents unaffected and is useful when the MAX525 is configured in a daisy chain (see the Daisy Chaining Devices section). The command to 10 change the clock edge on which serial data is shifted out of DOUT also loads data from all input registers to their respective DAC registers. Serial-Data Output (DOUT) The serial-data output, DOUT, is the internal shift register’s output. The MAX525 can be programmed so that data is clocked out of DOUT on SCLK’s rising edge (Mode 1) or falling edge (Mode 0). In Mode 0, output data at DOUT lags input data at DIN by 16.5 clock cycles, maintaining compatibility with Microwire™, SPI™/QSPI™, and other serial interfaces. In Mode 1, output data lags input data by 16 clock cycles. On power-up, DOUT defaults to Mode 0 timing. User-Programmable Logic Output (UPO) The user-programmable logic output, UPO, allows an external device to be controlled via the MAX525 serial interface (Table 1). ______________________________________________________________________________________ Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface MAX525 CS COMMAND EXECUTED SCLK 1 DIN 8 A0 A1 C1 D11 D10 C0 9 D8 D9 D7 16 D6 D5 D4 D3 D2 D1 D0 D6 D5 D4 D3 D2 D1 D0 DATA PACKET (N) DOUT (MODE 0) A0 A1 C1 C0 D11 D10 D8 D9 D7 A1 MSB FROM PREVIOUS WRITE DATA PACKET (N) DATA PACKET (N-1) DOUT (MODE 1) A1 A0 C1 C0 D11 D10 D8 D9 D7 D6 D5 D4 D3 D2 D1 D0 A1 MSB FROM PREVIOUS WRITE DATA PACKET (N) DATA PACKET (N-1) Figure 5. Serial-Interface Timing Diagram tCSW CS tCSO tCSS tCL tCP tCH tCSH tCS1 SCLK tDS tDH DIN tDO1 tDO2 DOUT Figure 6. Detailed Serial-Interface Timing Diagram Power-Down Lockout (PDL) The power-down lockout pin PDL disables software shutdown when low. When in shutdown, transitioning PDL from high to low wakes up the part with the output set to the state prior to shutdown. PDL could also be used to asynchronously wake up the device. Daisy Chaining Devices Any number of MAX525s can be daisy chained by connecting the DOUT pin of one device to the DIN pin of the following device in the chain (Figure 7). Since the MAX525’s DOUT pin has an internal active pull-up, the DOUT sink/source capability determines the time required to discharge/charge a capacitive load. Refer to the serial-data-out VOH and VOL specifications in the Electrical Characteristics. Figure 8 shows an alternate method of connecting several MAX525s. In this configuration, the data bus is common to all devices; data is not shifted through a daisy chain. More I/O lines are required in this configuration because a dedicated chip-select input (CS) is required for each IC. ______________________________________________________________________________________ 11 MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface MAX525 SCLK SCLK DIN DIN CS CS MAX525 SCLK DOUT MAX525 SCLK DOUT DIN CS DOUT DIN CS TO OTHER SERIAL DEVICES Figure 7. Daisy-Chaining MAX525s DIN SCLK CS1 CS2 TO OTHER SERIAL DEVICES CS3 CS CS MAX525 CS MAX525 MAX525 SCLK SCLK SCLK DIN DIN DIN Figure 8. Multiple MAX525s Sharing a Common DIN Line 12 ______________________________________________________________________________________ Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface Unipolar Output For a unipolar output, the output voltages and the reference inputs have the same polarity. Figure 9 shows the MAX525 unipolar output circuit, which is also the typical operating circuit. Table 2 lists the unipolar output codes. For rail-to-rail outputs, see Figure 10. This circuit shows the MAX525 with the output amplifiers configured with a closed-loop gain of +2 to provide 0V to 5V full-scale range when a 2.5V reference is used. Bipolar Output The MAX525 outputs can be configured for bipolar operation using Figure 11’s circuit. 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 corresponding output voltages for Figure 11’s circuit. Table 2. Unipolar Code Table REFERENCE INPUTS DAC CONTENTS MSB LSB ANALOG OUTPUT 1111 1111 1111 4095 +VREF ( ——— ) 4096 1000 0000 0001 2049 +VREF ( ——— ) 4096 1000 0000 0000 2048 +VREF +VREF ( ——— ) = ———— 4096 2 0111 1111 +5V MAX525 2047 +VREF ( ——— ) 4096 1111 0000 0000 0001 1 +VREF ( ——— ) 4096 0000 0000 0000 0V REFAB VDD REFCD FBA DAC A OUTA FBB DAC B OUTB FBC DAC C OUTC FBD DAC D OUTD AGND Table 3. Bipolar Code Table DAC CONTENTS MSB LSB ANALOG OUTPUT 1111 1111 1111 2047 +VREF ( ——— ) 2048 1000 0000 0001 1000 0000 0000 1 +VREF ( ——— ) 2048 0V 0111 1111 1111 1 -VREF ( ——— ) 2048 0000 0000 0001 2047 -VREF ( ——— ) 2048 0000 0000 0000 2048 -VREF ( ——— ) = -VREF 2048 Note: 1LSB = (VREF) ( 1 4096 DGND Figure 9. Unipolar Output Circuit ) ______________________________________________________________________________________ 13 MAX525 __________Applications Information Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface MAX525 Using an AC Reference REFERENCE INPUTS In applications where the reference has AC signal components, the MAX525 has multiplying capability within the reference input range specifications. Figure 12 shows a technique for applying a sine-wave signal to the reference input where the AC signal is offset before being applied to REFAB/REFCD. The reference voltage must never be more negative than DGND. The MAX525’s total harmonic distortion plus noise (THD + N) is typically less than -72dB, 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. +5V MAX525 REFAB FBA 10k VDD REFCD 10k DAC A OUTA FBB 10k 10k DAC B OUTB FBC 10k 10k Digitally Programmable Current Source DAC C The circuit of Figure 13 places an NPN transistor (2N3904 or similar) within the op-amp feedback loop to implement a digitally programmable, unidirectional current source. This circuit can be used to drive 4mA to 20mA current loops, which are commonly used in industrial-control applications. The output current is calculated with the following equation: OUTC FBD 10k 10k DAC D OUTD AGND DGND IOUT = (VREF / R) x (NB / 4096) where NB is the numeric value of the DAC’s binary input code and R is the sense resistor shown in Figure 13. VREFAB = VREFCD = 2.5V Figure 10. Unipolar Rail-to-Rail Output Circuit +5V R1 AC REFERENCE INPUT R2 26k 1/2 MAX492 REF_ +5V 500mVp-p FB_ 10k VDD REF_ VOUT DAC OUT_ -5V MAX525 DAC_ R1 = R2 = 10kΩ ± 0.1% OUT_ MAX525 AGND Figure 11. Bipolar Output Circuit 14 Figure 12. AC Reference Input Circuit ______________________________________________________________________________________ DGND Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface VL TOP VIEW MAX525 IOUT DAC_ OUT_ 2N3904 AGND 1 20 VDD FBA 2 19 FBD OUTA 3 FB_ 18 OUTD OUTB 4 R FBB 5 17 OUTC MAX525 Figure 13. Digitally Programmable Current Source 16 FBC 15 REFCD REFAB 6 CL 7 14 PDL CS 13 UPO 8 DIN 9 12 DOUT SCLK 10 11 DGND Power-Supply Considerations On power-up, all input and DAC registers are cleared (set to zero code) and DOUT is in Mode 0 (serial data is shifted out of DOUT on the clock’s falling edge). For rated MAX525 performance, limit REFAB/REFCD to less than 1.4V below VDD. Bypass VDD with a 4.7µF capacitor in parallel with a 0.1µF capacitor to AGND. Use short lead lengths and place the bypass capacitors as close to the supply pins as possible. DIP/SSOP Grounding and Layout Considerations Digital or AC transient signals between AGND and DGND can create noise at the analog outputs. Tie AGND and DGND together at the DAC, then tie this point to the highest-quality ground available. Good printed circuit board ground layout minimizes crosstalk between DAC outputs, reference inputs, and digital inputs. Reduce crosstalk by keeping analog lines away from digital lines. Wire-wrapped boards are not recommended. ______________________________________________________________________________________ 15 MAX525 __________________Pin Configuration REF_ MAX525 Low-Power, Quad, 12-Bit Voltage-Output DAC with Serial Interface _Ordering Information (continued) TRANSISTOR COUNT: 4337 INL (LSBs) PART TEMP. RANGE PIN-PACKAGE MAX525BC/D MAX525AEPP MAX525BEPP 0°C to +70°C -40°C to +85°C -40°C to +85°C Dice* 20 Plastic DIP 20 Plastic DIP ±1 ±1/2 ±1 20 SSOP 20 SSOP 20 CERDIP** 20 CERDIP** ±1/2 ±1 ±1/2 ±1 MAX525AEAP -40°C to +85°C MAX525BEAP -40°C to +85°C MAX525AMJP -55°C to +125°C MAX525BMJP -55°C to +125°C ___________________Chip Information * Dice are specified at TA = +25°C, DC parameters only. **Contact factory for availability and processing to MIL-STD-883. ________________________________________________________Package Information DIM α E H C L A A1 B C D E e H L α INCHES MILLIMETERS MAX MIN MIN MAX 0.078 0.068 1.73 1.99 0.008 0.002 0.05 0.21 0.015 0.010 0.25 0.38 0.008 0.004 0.09 0.20 SEE VARIATIONS 0.209 0.205 5.20 5.38 0.0256 BSC 0.65 BSC 0.311 0.301 7.65 7.90 0.037 0.025 0.63 0.95 8˚ 0˚ 0˚ 8˚ DIM PINS e SSOP SHRINK SMALL-OUTLINE PACKAGE A B A1 D D D D D 14 16 20 24 28 INCHES MILLIMETERS MAX MIN MAX MIN 6.33 0.239 0.249 6.07 6.33 0.239 0.249 6.07 7.33 0.278 0.289 7.07 8.33 0.317 0.328 8.07 0.397 0.407 10.07 10.33 21-0056A D . 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.