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How to prevent adc latch up

Question asked by meerkat on Feb 21, 2016
Latest reply on Feb 29, 2016 by JellenieR

Hello

we are  using AD7190  as ADC for load cell transmitter.

In some situation  ( in industrial environment ) the ADC latch up .

This is our schematic :

 

Capture.PNG

I have read this from AD7799 faq :

 

"The maximum dc current that these protection diodes can withstand is

10 mA. Therefore, the maximum current that can be applied to any input

is 10 mA. If it is possible for a current in excess of 10 mA to be applied

to a pin due to an overvoltage, external protection is required. Protection

schemes that can be applied include transzorbs on the power supply lines,

series resistors on digital input lines, and resistors and diodes on analog

inputs. For example, the external protection could be a resistor in series

with the input pin to limit the current into the pin to less than 10 mA. For

example, if the maximum overvoltage applied to a pin will be 5 V, a 1 kΩ

series resistor in each line will limit the current to 5 mA."

 

I have use SMBJ5CA for place between IN(+) and IN(-) .

and when i place this it didn't make any effect on adc result .

but as you know it need to be protected against GND and VCC.

Kik this :

2.PNG

But when I add D2 and D3 like above

The adc works nonlinear ! and add offset. (maybe the leakage cause this ).

Is there any specific schottky diode and TVS that you can recommend

that hasn't got these problem ?

 

 

Best Regards.

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