Unclear behavior of the TPS24710 hot swap controller.

Can you provide the scope waveform showing the current measurement? Is the current measurement captured at start up or after the output is fully operating (ie, apply the current limit after start up)?

Hi Eric,

The measurements were carried out after the output is fully operating (after start up), with open circuit at the output.

I used a multimeter and a kit of resistors for current measurement.

Regards,

    Svyatoslav.

I tried to change Rprog.

Rprog = 4.99K -> no changes.

Rprog = 3.57K -> no changes.

Rprog = spare -> the TPA24710 controller doesn't turn on.

Regards,

         Svyatoslav.

Once again I checked the current limit at Rprog=3.57K: 38.4 mA.

Regards,

        Svyatoslav.

Hi Eric,

whether there will be any recommendations?

Regards,

          Svyatoslav.

I suspect the issue is more signal-noise related (ie, small current limit sense signal vs. system bus noise). It wouldn't take much input bus ripple noise with this small current limit for you to see the errors you are seeing. Increasing input bus ripple will lower the effective current limit due to the low pass filter effects of the sense resistor and output load capacitor.

The error could also be related to the PCB routing of the sense inputs back to the IC (ie, any additional effective resistance between the real sense resistor and the IC sense amplifier will lower the effective current limit). Additional effective sense resistance could be caused by other circuits which might tap off the Kelvin routes back to the IC.

Have you tried a very clean, low ripple lab supply (or maybe you already have this) and only a resistive type load? If you still have the error in this ideal setup then maybe the source of the error is related to the Ksense. Other than that, you will have to conduct lab type investigative experiments to drill down to root cause. You might try modifying the EVM for your current limit and see if the issue persists with the EVM layout.

Hi Eric,

 concerning the K-sense routing, please see pcb layout in the attachment file.

The sense resistors are R635/634/633/632.

Regards,

              Svyatoslav.

Your Ksense routing looks good. Can you measure the mV between pins 8 and 9 using the DMM in mV mode to compare with the DMM measuring current?