AD5755 Non-Linearity

Document created by MCollins Employee on Feb 21, 2012
Version 1Show Document
  • View in full screen mode

Question

I'm getting a non-linear response on the output of the AD5755.  The Iout pin is connected to the Vout Pin.

As I increase the load resistance a gain and offset error enters my system measurement.  It appears that

there is another 30kOhm load connected between Iout and Gnd.

 

Answer

This is a result of the POC pin configuration.  See datasheet description as below. 


POC Pin
Power-On Condition. This pin determines the power-on condition and is read during power-on or, alternatively, after a device reset. If POC = 0, the device is powered up with the voltage and current channels in tristate mode. If POC = 1, the device is powered up with a 30 kΩ pull-down resistor to ground on the voltage output channel, and the current channel is in tristate mode.

 

POC bit
The POC bit determines the state of the voltage output channels during normal operation. Its default value is 0.
POC = 0. The output goes to the value set by the POC hardware pin when the voltage output is not enabled (default).
POC = 1. The output goes to the opposite value of the POC hardware pin if the voltage output is not enabled.

 

The solution is to tie the POC Hardware Pin Low OR leave POC pin as is and set POC bit high in Main Control register Bit D[12]

Attachments

    Outcomes