TPS4816-Q1: schematic check

Hi Sarah

Sorry, let me explain. The input voltage is normal, but there's no output.

Because Q2 lacks reverse connection protection, SRC is directly connected to the load, but the load has many capacitances, as shown in the red box in the diagram.

What impact will this have?

Thanks

Hi Gareth, 

I see. The output capacitance alone shouldn't be an issue until you turn on. It will create a lot of INRUSH current. 

If you are leaving the LPM and INP pins LOW, but getting a FLT this would be strange. Can you provide more information about the sequence of events? If FLT low automatically with a fresh VIN reset and LPM and INP low? 

Thanks,

Sarah

Hi Sarah

The LPM and INP pins circuitry is designed to pull high. Even after pulling the jumper down, there is still no voltage applied. Measurements show UVLO = 3.9V and I2T = 0.5V when the input voltage is 20V. After removing the input voltage, FLT returns to high.

Thanks

Hi Gareth, 

I am looking at this now and will get back to you soon. 

Thanks, 

Sarah

Hi Sarah

What exactly would cause a failure to conduct electricity?

Thanks

Hi Gareth, 

I'm confused by the circumstances again. 

You say FLT return High when VIN is removed? Where is FLT pin voltage coming from? 

If INP and INP_G are both low then there should be no current related FLT. 

But now I am noticing you do have TMP setup, but I only see one resistor on TMP. This is expected to have an RNTC and RTMP value. Can you confirm you are using an NTC thermistor there? 

You can try disabling TMP by floating TMP and directly GND ITMPO to verify if FLT_T is the issue. 

Thanks, 

Sarah

Hi Sarah

Following your suggestion, I tried floating TMP and directly GND ITMPO.

The test result showed that FLT was still LOW.

Can you also confirm the other questions? 

Thanks, 

Sarah

Hi Sarah

It's still in a faulty, no-output state. I'll try the TPS4812 EVM later. Please let me know if you have any other suggestions or waveforms that need measuring.

Hi Gareth, 

Yes, waveforms with OV and EN pin are helpful. 

You can also get waveform with INP, LPM, BST-SRC, VGS, and with the input voltage. Adding the FLT pin transitions relative to these would be helpful as well as TMR and I2T pins to see if any current FLT are being recognized. 

Thanks, 

Sarah

Hi Sarah

Measurement results are attached. Please assist in confirming. Thank you.

TPS4816_20260807.pdf

Hi Gareth, 

I am not finding precise explanation for FLT, but am seeing something odd here. 

I assume your BST and SRC waveforms are mislabeled. If so it looks like the BST is charging before the EN pin actually reaches EN HIGH. Are you pre biasing the CBST? 

Thanks, 

Sarah