LM74502: LM74502: LM74502 was never really resolved, I see the same issue on the LM74502 evaluation board

Klaus Moelholm

Part Number: LM74502

Tool/software:

The only difference is that I also see the problem on the LM74502H part:

When recovering from Over voltage protection, the LM74502(H) does not make a clean switch back to on, instead they are unstable until the input voltage is much below the OVF.

I have seen the fault situation with loads from 1 kOhm to 25 Ohm.

10 months ago

0 Shiven Dhir 10 months ago

TI__Mastermind 48475 points

Hi Klaus,

Is this repeatable? Can you share some waveforms of this behavior?

Regards,

Shiven Dhir

0 Klaus Moelholm 10 months ago in reply to Shiven Dhir

Prodigy 180 points

Hi,

Yes it is repeatable, just increase the input voltage until the LM74502H goes into OVP (37 V) and then reduce the input voltage to 33 V. This will start the oscillation shown on the waveforms. The load was 100 Ohm in this case.

LM74502H VIN2 33V.pdf

Best regards

Klaus

0 Shiven Dhir 10 months ago in reply to Klaus Moelholm

TI__Mastermind 48475 points

Hi Klaus,

Do you witness this behavior at loads <25ohms and loads >1k also?

Also, are the power cables very long?

Gate turn-on because of OV has its own response time of ~6us(typ) and is not able to recover due to VIN oscillations.

0 Klaus Moelholm 10 months ago

Prodigy 180 points

Hi,

I can not reproduce the fault with loads above 1 kOhm on the LM74502H.

I can reproduce the fault with loads down to 12 Ohms. With lower loads the power supply will go into current limiting, so I can't really test below 12 Ohm, but it look like the fault occurs with loads down to below 1 Ohm.

The power cables are about 50 cm long.

Best regards

Klaus