Programmable Voltage Output With Sense Connections Circuit
Design Goals
| DAC Output Voltage | Output Voltage VLOAD | Minimum Load Resistance RLOAD | Maximum Line Resistance Compensation | Error |
|---|---|---|---|---|
| 0V–5V | 0V–10V | 1kΩ | +25% of RLOAD | < 0.25% FSR |
Design Description
The programmable voltage output with sense connections circuit provides a precise voltage across a load, compensating for parasitic series resistance. The amplifier A1 uses feedback from the high-side and low-side of the attached load to accurately regulate the voltage between VSENSE+ and VSENSE-. The digital-to-analog converter (DAC) output and discrete resistors set the voltage across the load. This circuit is used in applications where additional line resistance can be present and must be compensated for by increasing the output voltage to deliver the correct voltage to the load. Common end equipment that use this circuit include analog output modules, memory and semiconductor test equipment, spectroscopy, and data acquisition (DAQ) cards.
Design Notes
- Select a DAC with low total unadjusted error (TUE) and with the required resolution for the application. A DAC with integrated reference, like the DAC80501 device, can be used to minimize components and solution size.
- Choose a high-voltage amplifier, with rail-to-rail output to provide a sufficient output swing to drive the load and line resistance. Set the amplifer to have low offset voltage and offset voltage drift so it does not significantly contribute to output error.
- Resistor mismatch directly contributes to gain error at the output. Use resistors with 0.05% tolerance or better and low thermal drift.
- For correct compensation of additional line resistance the ratio of R2:R4 must match the ratio of R3:R1 as closely as possible.
- The amplifier supply voltage is chosen based on the required output voltage, additional line resistance, and amplifier output swing at maximum load current.
- To reduce error at zero-scale a negative voltage can be supplied to the amplifier.
Design Steps
- The transfer function for VOUT based on DAC voltage
and resistor values is:
- A 50-kΩ resistance is chosen for R3. A relatively large value
should be selected to reduce the current in the feedback paths. R1 is then
calculated:
- R4 and R2 are chosen equal to R3 and R1, respectively.
- Calculate the maximum load current based on the minimum load
resistance and full scale VLOAD. The maximum load current impacts the
amplifier output voltage swing and the additional line resistance the circuit
can compensate.
- The required VCC voltage is calculated to drive 25%
additional load resistance and still maintain voltage regulation across
RLOAD. VO,rail is the approximate amplifier output
swing from V+ at a 10-mA load current.
- The output error can be approximated based on the DAC TUE,
amplifier offset voltage, resistor tolerance, and reference initial accuracy
using root sum square (RSS) analysis.
Figure 1-1 DC Transfer Characteristic
Figure 1-2 Small-Signal Step Response
Figure 1-3 Load Transient 10kΩ to 5kΩ
RLOAD
Figure 1-4 Maximum Additional Line Resistance at Amplifier VCC = 13VDevices
| Device | Key Features | Link | Other Possible Devices |
|---|---|---|---|
| DACs | |||
| DAC80501 | 16-bit resolution, 1-LSB INL, single-channel, voltage output DAC with 5ppm/°C internal reference | True 16-bit, 1-ch, SPI/I2C, voltage-output DAC in WSON package with precision internal reference | Precision DACs (≤10 MSPS) |
| DAC81416 | 16-bit resolution, 1-LSB INL, 16-channel ±20-V high-voltage output DAC with 5ppm/°C internal reference | 16-channel 16-bit high-voltage output DAC with integrated internal reference | |
| DAC80508 | 16-bit resolution, 1-LSB INL, octal-channel, voltage output DAC with 5ppm/°C internal reference | True 16-bit, 8-channel, SPI, voltage-output DAC with precision internal reference | |
| Op Amps | |||
| OPA196 | Low-offset (100µV), Low-drift, rail-to-rail I/O, 2.25V to 36V supply | Single, 36V, low power, all-purpose amplifier with mux-friendly input | Operational amplifiers (op amps) |
| TLV170 | Cost-sensitive, rail-to-rail output, 2.7V to 36V supply | Single, 36V, 1.2MHz, low-power operational amplifier for cost-sensitive applications | |
| OPA192 | Precision, ultra-low offset (5µV) and drift, rail-to-rail I/O, 4.5V to 36V supply | High-Voltage, Rail-to-Rail Input/Output, 5µV, 0.2µV/˚C, Precision Operational Amplifier | |
Links to Key Files
Texas Instruments, Programmable Voltage Output with Sense Connections, source files
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