Texas Instruments PGA309EVM-USB manual PGA309TestBoard Schematic Sensor Emulator Circuitry

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Figure 7 shows the sensor emulator circuit. The sensor emulator generates signals to help users evaluate the PGA309. No part of this circuit is required in your final design. The sensor emulator uses a DAC8555 (U8) to generate an emulated temperature signal, common-mode signal, and differential signal. These signals can be controlled using software to produce levels that closely match real-world sensors.

Figure 7. PGA309_Test_Board Schematic: Sensor Emulator Circuitry

The operational amplifier U4 and associated resistors is a differential amplifier with jumper selectable attenuation. The possible attenuations are 0.12 and 0.012. The attenuation produces a more accurate and stable emulated sensor output. For example, when the DAC outputs 3V, the sensor emulator outputs 3V × 0.012 = 36mV (assuming that attenuation is set in the 0.012 position). Thus, the maximum output of the sensor emulator is 120mV/V and 12mV/V.

The op amp U6 buffers the emulated temperature signal. Resistors R16, R17, R18, and R19 are used to attenuate the DAC output for temperature emulation and to reference the temperature signal to supply or ground. JMP13 allows the resistor network to be bypassed for direct connection to the DAC (diode temperature sensor mode).

10	PGA309EVM-USB	SBOU084 –February 2010
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