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LMP90080 Changing Power-State

Carsten Hyldal
Prodigy 60 points
Other Parts Discussed in Thread: LMP90080

Hi

We are using the LMP90080 for a PT100 sensor interface with a scan rate of 5Hz. The device is controlled by an FPGA.

The basic configuration of the device is ScanMode 1 (Multiple channels single scan), ODR = 214.65, FIRST_CH = 0 and LAST_CH = 6. When the device has finished conversion, it is entering stand-by state.

Every 200ms (5Hz scan rate) the power state is changed from stand-by state to active state.

Question #1:

What exactly happens, when the power state is changed from stand-by state to active state? It seems like the first sample isn't valid, after the power state has been changed. It actually looks like it is the old value for the LAST_CH from previous scan.

We are not doing a RESTART, which I have read can cause a problem like we have experienced:

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/306387.aspx

Could the change of power state cause the same problems as doing a RESTART?

Question #2:

When the power state is changed an additional delay of roughly 1ms is introduced between sample #1 and sample #2 (delay is roughly 5,6ms between sample #1 and sample #2). The delay between the remaining samples is roughly 4,66ms as expected due to ODR = 214.65. Could you provide any information regarding delays introduced by changing power state.

Thanks in advance for feedback.