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Troubles with AD5142

Hi! I cann't control AD5142 with stm32f4 by SPI. I connect AD5142 like rheostat in feedback of op amp (for amplifing). Scheme in attach. But when I send some data via SPI to AD5142 it don't answer and Vout isn't change. For change resistance, I send b0001000000000001 (in 16bit mode SPI in stm32f4), then I change data to b0001000011111111 and there is no result, Vout isn't change. Oscilloscope picture correct and looks same like in datasheet. What am I doing wrong? Is it necessary to send some preparation data to AD5142, before set resistance? Could some one post tested sequential data for change resistance in AD5142?

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  • Thank you for your answer!) Power of AD5142 is ok and gnd is common. AD5142 isn't answer via SPI. SDO line is always low, but I pull up it in stm32 internal pullup resistor.

    It's not pass filter, it's amplifier with programmeble gain. This scheme works correct with simple resistor (10k), but when I connect AD5142 -  Vout is like AD5142 = 5kohm and not changing. I try out 3 chips - all works same. Can it be problem in SPI data? What data should I send to see some data on SDO pin of AD5142?

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  • Thank you for your answer!) Power of AD5142 is ok and gnd is common. AD5142 isn't answer via SPI. SDO line is always low, but I pull up it in stm32 internal pullup resistor.

    It's not pass filter, it's amplifier with programmeble gain. This scheme works correct with simple resistor (10k), but when I connect AD5142 -  Vout is like AD5142 = 5kohm and not changing. I try out 3 chips - all works same. Can it be problem in SPI data? What data should I send to see some data on SDO pin of AD5142?

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