TPS48111Q1EVM: Issues with overcurrent protection

Riccardo Ierardi

Prodigy 120 points

Part Number: TPS48111Q1EVM
Other Parts Discussed in Thread: ALLIGATOR

Tool/software:

Dear Support,

I'm having difficulties in using the EVM for TPS48111Q1. I'm trying to drive loads at 24V, in the following conditions:

No load using precharge path: output works correctly
100 ohm load using precharge path, with 100ohm connected after precharge completes: output works correctly
100 ohm load using precharge path, with 100ohm connected at startup: precharge works up until a level, as expected, then turning on the load triggers current fault (I guess too much current is still drawn into the load capacitors)
1 ohm load using precharge path, with 1 ohm load connected after precharge completes: turning on the load triggers current fault

The board is configured as follows:

50A current protection (no changes if current protection is completely disabled, so i guess ISCP triggers protection)
tested also without input capacitor C16 (in order to read the real current input from the power supply), no current spike detected coming from power supply

I can't understand why the board can't drive the 24A to the load without triggering protection. No current spikes are present on both inputs and outputs.

Here the example with 1 ohm load connected after precharge has been completed (condition 4):

Yellow: Vin

Red: Vout

Blue: Iin

Green: Iout

Thank you,

Kind Regards

11 months ago

0 Sarah Raines 11 months ago

TI__Expert 8620 points

Hello,

It seems like you may be using an electronic load in constant current mode. This would explain why the device shuts off earlier than expected.
Please use a constant resistance mode instead.

Thank you,

Sarah

0 Riccardo Ierardi 11 months ago in reply to Sarah Raines

Prodigy 120 points

Hello Sarah,

thank you for the quick reply. Actually I'm using an actual power resistor, this family to be precise https://www.te.com/en/product-CAT-C339-T2201.html

Thank you,

Kind Regards

0 Sarah Raines 11 months ago in reply to Riccardo Ierardi

TI__Expert 8620 points

Hi Riccardo,

I see. Please clarify a few things:

1.) Have you tried a resistive electronic load and this does not work as expected either?

2.) For the resistor you linked I assume you have 1 version that is 100 ohm and one that is 1 ohm?

3.) Are you connecting this to the EVM using alligator clips?

4.) Is there any bulk capacitance on the load as well?

Thank you,

Sarah

0 Riccardo Ierardi 11 months ago in reply to Sarah Raines

Prodigy 120 points

Hello Sarah,

1. No not yet, being unable to use it with a resistor stopped me to try further with an electronic load

2. Yes

3. No, I'm using the high current screw joint provided with the demoboard

4. The one provided with EVM. They should work using the precharge path

0 Sarah Raines 11 months ago in reply to Riccardo Ierardi

TI__Expert 8620 points

Hi Riccardo,

Firstly, I would recommend trying a different load to ensure that this could not be the cause.

Second, are you seeing D4 come on?

Third, I see a small dip in your waveform at Vin and Vout. The scale is too small to see what this drop is. Are you changing the input voltage?

Thanks,

Sarah

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TPS48111Q1EVM: Issues with overcurrent protection