TPS404022 Output Current Export

Hi Kami,

Thank you for your interest in TI parts. The output current reporting is the average inductor current, which should be the same as the average load current. The 40422 measures the DC voltage across the capacitor in the R-C filter across the inductor. This DC voltage is quite small (and noisy), so the gain in the sensing circuit is quite high and subject to gain and offset errors. So the device needs to be calibrated for gain and offset once it is placed in a particular system, in this case the EVM. The device is not finely calibrated in production, so the end user should perform the calibration. First calibrate offset, then gain.

In order to calibrate offset:

1) Set load to 0A (or just disconnect it, but make sure it is 0A). Use an input voltage close to the expected nominal system Vin.

2) In the "Configure: Other" pane, scroll the IOUT_CAL_OFFSET to the same number as the GUI read-out for the particular rail in question.

3) The select the "Write to Hardware" button.

4) Then select the "Store Config to NVM" button (Non-Volatile Memory).

Done.

To calibrate the IOUT_CAL_GAIN:

1) Connect the output to full load (the EVM 1.2V rail full load is 20A).

2) In the "Configure: Other" pane, scroll the IOUT_CAL_GAIN to a number that provides the correct GUI read-out current for the particular rail in question at the applied load. Ideally this should be the DCR of the output inductor, but non-ideal layout will affect this calibration. This number is configured in production to the nominal inductor manufacturer specified DCR, but not calibrated to an actual measurement in situ.

3) The select the "Write to Hardware" button.

4) Then select the "Store Config to NVM" button.

Done.

Take care,

MC.

Dear Mc.

Thanks. Very clear and I will try it.

Best Regards,

Kami Huang

Hi Kami,

I noticed a few errors in my post, sorry. I have made some corrections, in red font.

MC.

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.... The device is not finely calibrated on the EVM in production, so the end user should perform the calibration. First calibrate offset, then gain.

In order to calibrate offset:

1) Set load to 0A (or just disconnect it, but make sure it is 0A). Use an input voltage close to the expected nominal system Vin.

2) In the "Configure: Other" pane, scroll the IOUT_CAL_OFFSET to the same but opposite polarity number as the GUI read-out for the particular rail in question. I don't have the GUI in front of me now, but I believe the offset should be the negative of the zero load reported current. So for example, if at no load the GUI reports 0.5A, you should enter an offset of -0.5A.

3) Then select the "Write to Hardware" button.

4) Then select the "Store Config to NVM" button (Non-Volatile Memory).

Done.

To calibrate the IOUT_CAL_GAIN:

1) Connect the output to full load (the EVM 1.2V rail full load is 20A).

2) In the "Configure: Other" pane, scroll the IOUT_CAL_GAIN to a number that provides the correct GUI read-out current for the particular rail in question at the applied load. Ideally this should be the DCR of the output inductor, but non-ideal layout will affect this calibration. This number is configured in production to the nominal inductor manufacturer specified DCR, but not calibrated to an actual measurement in situ.

3) Then select the "Write to Hardware" button.

4) Then select the "Store Config to NVM" button.

Done.

Take care,

MC.