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AD8436 noise senstivity at startup

Question asked by robin.hu Employee on Nov 22, 2013
Latest reply on Jan 29, 2014 by jstaley

Use AD8436 on DMM project, encoutered trouble as following:

1) with 0mV input (AC input grounded with 100kOhm), after power up, AD8436 firstly got 0mV output, then had ~2mV output after 10-30s, the duration was not fixed, ie some times longer and sometimes shorter. after the duration, the output of AD8436 stick to ~2mV later

- See attached picture for the test setup with EVB.

- AC couple, IBUF enabble, OBUF enable, dual supply+/-3V, 100kOhm to ground.

 

2) Expect the output AD8436 can be kept at 0mV

- Compared with AD637, the inital output of AD637(0mV input) is typically x-mV level then getting down to 0mV, it is acceptable and almost no need for calibration.

- with AD8436, the initial output(0mV input) is 0mV, but will ramp up to a stable value of x-mV level.

- if the ramp up duration is short, the error/offset can be calibrated out with software.

*** So the trouble is the duration is too long and not feasible for possible calibration.

See attached schematic of the end-application.  

 

Need help to identify how to reduce the noise at input and understand why the time for output ramp up is varied.

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