LTC1657 Parallel 16-Bit Rail-to-Rail Micropower DAC U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®1657 is a complete single supply, rail-to-rail voltage output, 16-bit digital-to-analog converter (DAC) in a 28-pin SSOP or PDIP package. It includes a rail-to-rail output buffer amplifier, an internal 2.048V reference and a double buffered parallel digital interface. 16-Bit Monotonic Over Temperature Deglitched Rail-to-Rail Voltage Output: 8nV•s 5V Single Supply Operation ICC: 650µA Typ Maximum DNL Error: ±1LSB Settling Time: 20µs to ±1LSB Internal or External Reference Internal Power-On Reset to Zero Volts Asynchronous CLR Pin Output Buffer Configurable for Gain of 1 or 2 Parallel 16-Bit or 2-Byte Double Buffered Interface Narrow 28-Lead SSOP Package Multiplying Capability The LTC1657 operates from a 4.5V to 5.5V supply. It has a separate reference input pin that can be driven by an external reference. The full-scale output can be 1 or 2 times the reference voltage depending on how the X1/X2 pin is connected. The LTC1657 is similar to Linear Technology Corporation’s LTC1450 12-bit VOUT DAC family allowing an upgrade path. It is the only buffered 16-bit parallel DAC in a 28-lead SSOP package and includes an onboard reference for stand alone performance. U APPLICATIO S ■ ■ ■ ■ ■ Instrumentation Digital Calibration Industrial Process Control Automatic Test Equipment Communication Test Equipment , LTC and LT are registered trademarks of Linear Technology Corporation. W BLOCK DIAGRA 5V 19 D15 (MSB) 18 23 22 REFOUT REFHI 24 VCC REFERENCE 2.048V 17 MSB 8-BIT INPUT REGISTER 16 15 14 Differential Nonlinearity vs Input Code 13 12 1.0 16-BIT DAC REGISTER D8 11 D7 10 16-BIT DAC + – 9 8 7 6 VOUT LSB 8-BIT INPUT REGISTER R R 5 4 D0 (LSB) 3 CSMSB FROM MICROPROCESSOR DECODE LOGIC 1 WR FROM SYSTEM RESET 27 CLR 0.8 0.6 0.4 0.2 0.0 –0.2 –0.4 –0.6 –0.8 –1.0 0 2 CSLSB 28 LDAC 25 0V TO 4.096V DIFFERENTIAL NONLINEARITY (LSB) DATA IN FROM MICROPROCESSOR DATA BUS 16384 32768 49152 DIGITAL INPUT CODE 65535 1657 G01 POWER-ON RESET GND 20 REFLO X1/X2 21 26 1657 TA01 1 LTC1657 U W U U W W W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) VCC to GND .............................................. – 0.5V to 7.5V TTL Input Voltage, REFHI, REFLO, X1/X2 ....................................................... – 0.5V to 7.5V VOUT, REFOUT ............................ – 0.5V to (VCC + 0.5V) Operating Temperature Range LTC1657C ............................................. 0°C to 70°C LTC1657I ........................................ – 40°C to 85°C Maximum Junction Temperature .......................... 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER TOP VIEW WR 1 28 LDAC CSLSB 2 27 CLR CSMSB 3 26 X1/X2 (LSB) D0 4 25 VOUT D1 5 24 VCC D2 6 23 REFOUT D3 7 22 REFHI D4 8 21 REFLO D5 9 20 GND LTC1657CGN LTC1657CN LTC1657IGN LTC1657IN D6 10 19 D15 (MSB) D7 11 18 D14 D8 12 17 D13 D9 13 16 D12 D10 14 15 D11 N PACKAGE 28-LEAD PDIP GN PACKAGE 28-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 95°C/ W (G) TJMAX = 125°C, θJA = 58°C/ W (N) Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 4.5V to 5.5V, VOUT unloaded, REFOUT tied to REFHI, REFLO tied to GND, X1/X2 tied to GND, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS DAC (Note 2) Resolution Monotonicity ● 16 ● 16 Bits Bits DNL Differential Nonlinearity Guaranteed Monotonic (Note 3) ● ±0.5 ±1.0 LSB INL Integral Nonlinearity (Note 3) ● ±4 ±12 LSB 2 mV ±0.3 ±3 mV ZSE Zero Scale Error VOS Offset Error VOSTC Offset Error Tempco ● Measured at Code 200 0 ● ±5 Gain Error ±2 ● Gain Error Drift µV/°C ±16 0.5 LSB ppm/°C Power Supply VCC Positive Supply Voltage For Specified Performance ● 5.5 V ICC Supply Current 4.5V ≤ VCC ≤ 5.5V (Note 4) ● 4.5 650 1200 µA Short-Circuit Current Low VOUT Shorted to GND ● 70 120 mA Short-Circuit Current High VOUT Shorted to VCC ● 80 140 mA Output Impedance to GND Input Code = 0 ● 40 120 Ω Output Line Regulation Input Code = 65535, VCC = 4.5V to 5.5V ● Op Amp DC Performance 2 4 mV/V LTC1657 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 4.5V to 5.5V, VOUT unloaded, REFOUT tied to REFHI, REFLO tied to GND, X1/X2 tied to GND, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP ±0.3 ±0.7 MAX UNITS AC Performance Voltage Output Slew Rate (Note 5) Voltage Output Settling Time (Note 5) to 0.0015% (16-Bit Settling Time) (Note 5) to 0.012% (13-Bit Settling Time) ● Digital Feedthrough Midscale Glitch Impulse DAC Switch Between 8000H and 7FFFH Output Voltage Noise Spectral Density At 1kHz V/µs 20 10 µs µs 0.3 nV •s 8 nV •s 250 nV/√Hz Digital I/O VIH Digital Input High Voltage ● 2.4 V VIL Digital Input Low Voltage ● VOH Digital Output High Voltage ● VOL Digital Output Low Voltage ● 0.4 V ILEAK Digital Input Leakage VIN = GND to VCC ● ±10 µA CIN Digital Input Capacitance (Note 6) 10 pF 0.8 VCC – 1 V V Switching Characteristics tCS CS (MSB or LSB) Pulse Width ● 40 ns tWR WR Pulse Width ● 40 ns tCWS CS to WR Setup ● 0 ns tCWH CS to WR Hold ● 0 ns tDWS Data Valid to WR Setup ● 40 ns tDWH Data Valid to WR Hold ● 0 ns tLDAC LDAC Pulse Width ● 40 ns tCLR CLR Pulse Width ● 40 ns ● 2.036 Reference Output (REFOUT) Reference Output Voltage Reference Output Temperature Coefficient 2.048 2.060 15 V ppm/°C Reference Line Regulation VCC = 4.5V to 5.5V ● ±1.5 mV/V Reference Load Regulation Measured at IOUT = 100µA ● 5 mV/A Short-Circuit Current REFOUT Shorted to GND ● (Note 6) See Applications Information X1/X2 Tied to VOUT X1/X2 Tied to GND ● ● 0 0 ● 16 50 100 mA Reference Input REFHI, REFLO Input Range REFHI Input Resistance Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: External reference REFHI = 2.2V. VCC = 5V. Note 3: Nonlinearity is defined from code 128 to code 65535 (full scale). See Applications Information. VCC – 1.5 VCC /2 25 V V kΩ Note 4: Digital inputs at 0V or VCC. Note 5: DAC switched between all 1s and all 0s. Note 6: Guaranteed by design. Not subject to test. 3 LTC1657 U W TYPICAL PERFOR A CE CHARACTERISTICS Minimum Supply Headroom for Full Output Swing vs Load Current Integral Nonlinearity 5 2.0 0.8 4 1.8 3 1.6 2 1.4 0.6 0.4 0.2 0.0 –0.2 –0.4 –0.6 –0.8 –1.0 VCC – VOUT (V) 1.0 INTEGRAL NONLINEARITY (LSB) DIFFERENTIAL NONLINEARITY (LSB) Differential Nonlinearity 1 0 –1 16384 32768 49152 DIGITAL INPUT CODE 0.4 –4 0.2 –55°C 16384 32768 49152 DIGITAL INPUT CODE 65535 0 5 LOAD CURRENT (mA) 1657 G02 Offset Error vs Temperature 4.110 CODE ALL 0’S ∆VOUT ≤ 1LSB 10 1657 G03 Full-Scale Voltage vs Temperature 1.2 1.0 0.9 4.105 0.8 0.6 25°C 0.4 –55°C 0.8 0.7 4.100 OFFSET (mV) 125°C FULL-SCALE VOLTAGE (V) OUTPUT PULL-DOWN VOLTAGE (V) 25°C 0 0 Minimum Output Voltage vs Output Sink Current 0.2 0.8 –3 1657 G01 1.0 1.0 0.6 65535 125°C 1.2 –2 –5 0 CODE ALL 1’S ∆VOUT ≤ 1LSB 4.095 4.090 0.6 0.5 0.4 0.3 0.2 4.085 0.1 0 0 5 10 OUTPUT SINK CURRENT (mA) 4.080 –55 15 –25 5 35 65 TEMPERATURE (°C) 1657 G04 95 0 –55 125 1657 G05 Supply Current vs Logic Input Voltage 700 7 680 Large-Signal Transient Response 5 VOUT UNLOADED TA = 25°C 4 4 3 2 OUTPUT VOLTAGE (V) SUPPLY CURRENT (µA) SUPPLY CURRENT (mA) 660 5 640 620 VCC = 5.5V 600 VCC = 5V 580 VCC = 4.5V 560 0 2 520 0 1 2 3 4 LOGIC INPUT VOLTAGE (V) 5 1657 G07 4 3 1 540 1 125 1657 G06 Supply Current vs Temperature 8 6 –10 35 80 TEMPERATURE (°C) 500 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1657 G08 0 TIME (20µs/DIV) 1657 G09 LTC1657 U U U PIN FUNCTIONS WR (Pin 1): Write Input (Active Low). Used with CSMSB and/or CSLSB to control the input registers. While WR and CSMSB and/or CSLSB are held low, data writes into the input register. CSLSB (Pin 2): Chip Select Least Significant Byte (Active Low). Used with WR to control the LSB 8-bit input registers. While WR and CSLSB are held low, the LSB byte writes into the LSB input register. Can be connected to CSMSB for simultaneous loading of both sets of input latches on a 16-bit bus. CSMSB (Pin 3): Chip Select Most Significant Byte (Active Low). Used with WR to control the MSB 8-bit input registers. While WR and CSMSB are held low, the MSB byte writes into the MSB input register. Can be connected to CSLSB for simultaneous loading of both sets of input latches on a 16-bit bus. D0 to D7 (Pins 4 to 11): Input data for the Least Significant Byte. Written into LSB input register when WR = 0 and CSLSB = 0. D8 to D15 (Pins 12 to 19): Input data for the Most Significant Byte. Written into MSB input register when WR = 0 and CSMSB = 0. GND (Pin 20): Ground. REFLO (Pin 21): Lower input terminal of the DAC’s internal resistor ladder. Typically connected to Analog Ground. An input code of (0000)H will connect the positive input of the output buffer to this end of the ladder. Can be used to offset the zero scale above ground. REFHI (Pin 22): Upper input terminal of the DAC’s internal resistor ladder. Typically connected to REFOUT. An input code of (FFFF)H will connect the positive input of the output buffer to 1LSB below this voltage. REFOUT (Pin 23): Output of the internal 2.048V reference. Typically connected to REFHI to drive internal DAC resistor ladder. VCC (Pin 24): Positive Power Supply Input. 4.5V ≤ VCC ≤ 5.5V. Requires a 0.1µF bypass capacitor to ground. VOUT (Pin 25): Buffered DAC Output. X1/X2 (Pin 26): Gain Setting Resistor Pin. Connect to GND for G = 2 or to VOUT for G = 1. This pin should always be tied to a low impedance source, such as ground or VOUT, to ensure stability of the output buffer when driving capacitive loads. CLR (Pin 27): Clear Input (Asynchronous Active Low). A low on this pin asynchronously resets all input and DAC registers to 0s. LDAC (Pin 28): Load DAC (Asynchronous Active Low). Used to asynchronously transfer the contents of the input registers to the DAC register which updates the output voltage. If held low, the DAC register loads data from the input registers which will immediately update VOUT. 5 LTC1657 U DIGITAL INTERFACE TRUTH TABLE CLR CSMSB CSLSB WR LDAC L H H H H H H H H H X X X L H L X H X L X X X H L L X X H L X X X L L L H X X L X L H X X X X X X L FUNCTION Clears input and DAC registers to zero Loads DAC register with contents of input registers Freezes contents of DAC register Writes MSB byte into MSB input register Writes LSB byte into LSB input register Writes MSB and LSB bytes into MSB and LSB input registers Inhibits write to MSB and LSB input registers Inhibits write to MSB input register Inhibits write to LSB input register Data bus flows directly through input and DAC registers W UW TIMING DIAGRAM t CS CSLSB t CS CSMSB t CWS t WR t CWH t WR WR t LDAC LDAC t DWH t DWS DATA DATA VALID DAC UPDATE DATA VALID 1657 TD 6 LTC1657 U U DEFI ITIO S Resolution (n): Resolution is defined as the number of digital input bits (n). It defines the number of DAC output states (2n) that divide the full-scale range. Resolution does not imply linearity. Full-Scale Voltage (VFS): This is the output of the DAC when all bits are set to 1. Voltage Offset Error (VOS): Normally, the DAC offset is the voltage at the output when the DAC is loaded with all zeros. The DAC can have a true negative offset, but because the part is operated from a single supply, the output cannot go below zero. If the offset is negative, the output will remain near 0V resulting in the transfer curve shown in Figure 1. 0V Integral Nonlinearity (INL): End-point INL is the maximum deviation from a straight line passing through the end points of the DAC transfer curve. Because the part operates from a single supply and the output cannot go below zero, the linearity is measured between full scale and the code corresponding to the maximum offset specification. The INL error at a given input code is calculated as follows: INL (In LSBs) = [VOUT – VOS – (VFS – VOS) (code/65535)] VOUT = The output voltage of the DAC measured at the given input code OUTPUT VOLTAGE NEGATIVE OFFSET Zero-Scale Error (ZSE): The output voltage when the DAC is loaded with all zeros. Since this is a single supply part, this value cannot be less than 0V. DAC CODE 1657 F01 Figure 1. Effect of Negative Offset The offset of the part is measured at the code that corresponds to the maximum offset specification: VOS = VOUT – [(Code)(VFS)/(2n – 1)] Least Significant Bit (LSB): One LSB is the ideal voltage difference between two successive codes. Differential Nonlinearity (DNL): DNL is the difference between the measured change and the ideal one LSB change between any two adjacent codes. The DNL error between any two codes is calculated as follows: DNL = (∆VOUT – LSB)/LSB ∆V OUT = The measured voltage difference between two adjacent codes Digital Feedthrough: The glitch that appears at the analog output caused by AC coupling from the digital inputs when they change state. The area of the glitch is specified in nV • s. LSB = (VFS – VOS)/(2n – 1) = (VFS – VOS)/65535 Nominal LSBs: LTC1657 LSB = 4.096V/65535 = 62.5µV DAC Transfer Characteristic: REFHI – REFLO VOUT = G • CODE + REFLO 65536 ( ) G = 1 for X1/X2 connected to VOUT G = 2 for X1/X2 connected to GND CODE = Decimal equivalent of digital input (0 ≤ CODE ≤ 65535) 7 LTC1657 U OPERATION Parallel Interface The data on the input of the DAC is written into the DAC’s input registers when Chip Select (CSLSB and/or CSMSB) and WR are at a logic low. The data that is written into the input registers will depend on which of the Chip Selects are at a logic low (see Digital Interface Truth Table). If WR and CSLSB are both low and CSMSB is high, then only data on the eight LSBs (D0 to D7) is written into the input registers. Similarly, if WR and CSMSB are both low and CSLSB is high, then only data on the eight MSBs (D8 to D15) is written into the input registers. Data is written into both the Least Significant Data Bits (D0 to D7) and the Most Significant Bits (D8 to D15) at the same time if WR, CSLSB and CSMSB are low. If WR is high or both CSMSB and CSLSB are high, then no data is written into the input registers. Once data is written into the input registers, it can be written into the DAC register. This will update the analog voltage output of the DAC. The DAC register is written by a logic low on LDAC. The data in the DAC register will be held when LDAC is high. When WR, CSLSB, CSMSB and LDAC are all low, the registers are transparent and data on pins D0 to D15 flows directly into the DAC register. For an 8-bit data bus connection, tie the MSB byte data pins to their corresponding LSB byte pins (D15 to D7, D14 to D6, etc). Power-On Reset The LTC1657 has an internal power-on reset that resets all internal registers to 0’s on power-up (equivalent to the CLR pin function). Reference The LTC1657 includes an internal 2.048V reference, giving the LTC1657 a full-scale range of 4.096V in the gainof-2 configuration. The onboard reference in the LTC1657 is not internally connected to the DAC’s reference resistor string but is provided on an adjacent pin for flexibility. Because the internal reference is not internally connected 8 to the DAC resistor ladder, an external reference can be used or the resistor ladder can be driven by an external source in multiplying applications. The external reference or source must be capable of driving the 16k (minimum) DAC ladder resistance. Internal reference output noise can be reduced with a bypass capacitor to ground. (Note: The reference does not require a bypass capacitor to ground for nominal operation.) When bypassing the reference, a small value resistor in series with the capacitor is recommended to help reduce peaking on the output. A 10Ω resistor in series with a 4.7µF capacitor is optimum for reducing reference generated noise. Internal reference output voltage noise spectral density at 1kHz is typically 150nV/√Hz. DAC Resistor Ladder The high and low end of the DAC ladder resistor string (REFHI and REFLO, respectively) are not connected internally on this part. Typically, REFHI will be connected to REFOUT and REFLO will be connected to GND. X1/X2 connected to GND will give the LTC1657 a full-scale output swing of 4.096V. Either of these pins can be driven up to VCC – 1.5V when using the buffer in the gain-of-1 configuration. The resistor string pins can be driven to VCC/2 when the buffer is in the gain of 2 configuration. The resistance between these two pins is typically 25k (16k min). Voltage Output The output buffer for the LTC1657 can be configured for two different gain settings. By tying the X1/X2 pin to GND, the gain is set to 2. By tying the X1/X2 pin to VOUT, the gain is set to unity. The LTC1657 rail-to-rail buffered output can source or sink 5mA within 500mV of the positive supply voltage or ground at room temperature. The output stage is equipped with a deglitcher that results in a midscale glitch impulse of 8nV • s. The output swings to within a few millivolts of either supply rail when unloaded and has an equivalent output resistance of 40Ω when driving a load to the rails. LTC1657 U U W U APPLICATIONS INFORMATION Rail-to-Rail Output Considerations In any rail-to-rail DAC, the output swing is limited to voltages within the supply range. If the DAC offset is negative, the output for the lowest codes limits at 0V as shown in Figure 1b. Similarly, limiting can occur near full scale when the REF pin is tied to VCC /2. If VREF = VCC /2 and the DAC full-scale error (FSE) is positive, the output for the highest codes limits at VCC as shown in Figure 1c. No full-scale limiting can occur if VREF is less than (VCC – FSE)/2. Offset and linearity are defined and tested over the region of the DAC transfer function where no output limiting can occur. VCC VREF = VCC /2 POSITIVE FSE OUTPUT VOLTAGE INPUT CODE (c) VCC VREF = VCC /2 OUTPUT VOLTAGE 0 32768 INPUT CODE (a) 65535 OUTPUT VOLTAGE 0V NEGATIVE OFFSET INPUT CODE (b) 1657 F02 Figure 2. Effects of Rail-to-Rail Operation On a DAC Transfer Curve. (a) Overall Transfer Function (b) Effect of Negative Offset for Codes Near Zero Scale (c) Effect of Positive Full-Scale Error for Input Codes Near Full Scale When VREF = VCC /2 9 LTC1657 U TYPICAL APPLICATIO S the onboard reference is always sourcing current and never has to sink any current even when VOUT is at full scale. The LT1077 output will have a wide bipolar output swing of – 4.096V to 4.096V as shown in the figure below. With this output swing, 1LSB = 125µV. This circuit shows how to make a bipolar output 16-bit DAC with a wide output swing using an LTC1657 and an LT1077. R1 and R2 resistively divide down the LTC1657 output and an offset is summed in using the LTC1657 onboard 2.048V reference and R3 and R4. R5 ensures that A Wide Swing, Bipolar Output 16-Bit DAC 5V 0.1µF 24 5:19 DATA (0:15) 2 CSLSB 3 µP VCC CSMSB 1 VOUT LTC1657 WR 28 25 R1 100k 1% LDAC 27 CLR X1/X2 REFLO GND 26 21 REFHI REFOUT 20 22 23 R2 200k 1% TRANSFER CURVE 4.096 5V 3 7 + 6 LT1077 2 – R3 100k 1% VOUT: (2)(DIN)(4.096) – 4.096V 65536 4 R4 – 5V 200k 1% 1657 TA05 VOUT 32768 0 65535 DIN R5 100k 1% – 4.096 This circuit shows a digitally programmable current source from an external voltage source using an external op amp, an LT1218 and an NPN transistor (2N3440). Any digital word from 0 to 65535 is loaded into the LTC1657 and its output correspondingly swings from 0V to 4.096V. This voltage will be forced across the resistor RA. If RA is chosen to be 412Ω, the output current will range from 0mA at zero scale to 10mA at full scale. The minimum voltage for VS is determined by the load resistor RL and Q1’s VCESAT voltage. With a load resistor of 50Ω, the voltage source can be 5V. Digitally Programmable Current Source 5V 22 5:19 2 µP 3 1 28 27 DATA (0:15) 23 5V < VS < 100V FOR RL ≤ 50Ω 0.1µF REFHI REFOUT VCC CSLSB CSMSB LTC1657 VOUT WR 3 + X1/X2 REFLO GND 26 21 2 – RL 7 LT1218 LDAC CLR 25 6 Q1 2N3440 (DIN)(4.096) (65536)(RA) ≈ 0mA TO 10mA IOUT = 4 20 RA 412Ω 1% 1657 TA04 10 LTC1657 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. GN Package 28-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.386 – 0.393* (9.804 – 9.982) 0.033 (0.838) REF 28 27 26 25 24 23 22 21 20 19 18 17 1615 0.229 – 0.244 (5.817 – 6.198) 0.150 – 0.157** (3.810 – 3.988) 1 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.0075 – 0.0098 (0.191 – 0.249) 2 3 4 5 6 7 8 9 10 11 12 13 14 0.053 – 0.069 (1.351 – 1.748) 0.004 – 0.009 (0.102 – 0.249) 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.0250 (0.635) BSC 0.008 – 0.012 (0.203 – 0.305) * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE GN28 (SSOP) 1098 N Package 28-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 1.370* (34.789) MAX 28 27 26 25 24 23 22 21 20 19 18 17 16 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0.255 ± 0.015* (6.477 ± 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 0.020 (0.508) MIN 0.009 – 0.015 (0.229 – 0.381) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 ) 0.125 (3.175) MIN 0.065 (1.651) TYP 0.005 (0.127) MIN 0.100 (2.54) BSC 0.018 ± 0.003 (0.457 ± 0.076) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) 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. N28 1098 11 LTC1657 U TYPICAL APPLICATIO This circuit shows how to measure negative offset. Since LTC1657 operates on a single supply, if its offset is negative, the output for code 0 limits at 0V. To measure this negative offset, a negative supply is needed, connect resistor R1 as shown in the figure. The output voltage is the negative offset when code 0 is loaded in. Negative Offset Measurement 5V 22 5:19 2 3 µP 1 28 27 23 24 0.1µF REFHI REFOUT VCC DATA (0:15) CSLSB CSMSB LTC1657 VOUT WR 25 R1 100k LDAC CLR X1/X2 REFLO GND 26 21 –5V 20 1657 TA06 Although LTC1657 output is up to 4.096V with its internal reference, higher voltages can be achieved with the help of another op amp. The following circuit shows how to increase the output swing of LTC1657 by using an LT1218. As shown in the configuration, the output of LTC1657 is amplified by 8 for an output swing of 0V to 32.768V, or a convenient 0.5mV/LSB. A Higher Voltage Output DAC TRANSFER CURVE VOUT 5V 22 5:19 2 3 µP 1 28 27 DATA (0:15) 23 0.1µF 36V 24 REFHI REFOUT VCC 32.768 (V) 0.1µF CSLSB CSMSB LTC1657 VOUT WR 25 + 7 LT1218 LDAC CLR 3 X1/X2 REFLO GND 26 21 2 – 6 VOUT = 4 20 R1 1k 1% ( ) (DIN)(4.096) R2 1+ 65536 R1 0 R2 6.98k 1% 65535 DIN 1657 TA07 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1446(L) Dual 12-Bit VOUT DACs in SO-8 Package VCC = 5V (3V), VOUT = 0V to 4.095V (0V to 2.5V) LTC1450(L) Single 12-Bit VOUT DACs with Parallel Interface VCC = 5V (3V), VOUT = 0V to 4.095V (0V to 2.5V) LTC1458(L) Quad 12-Bit Rail-to-Rail Output DACs with Added Functionality VCC = 5V (3V), VOUT = 0V to 4.095V (0V to 2.5V) LTC1650 Single 16-Bit VOUT Industrial DAC in 16-Pin SO VCC = ±5V, Low Power, Deglitched, 4-Quadrant Multiplying VOUT LTC1655(L) Single 16-Bit VOUT DAC with Serial Interface in SO-8 VCC = 5V (3V), Low Power, Deglitched, VOUT = 0V to 4.096V (0V to 2.5V) 12 Linear Technology Corporation 1657f LT/TP 0400 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1999