LM5060: OVP target not being hit

Cameron Perl

Expert 3990 points

Part Number: LM5060

Hey team,

A customer is having an issue with 3 prototypes with the following targets / specs:

OVP = 67 V

UVLO = 35 V

R1 = 200k, R2 = 3.3k, and R3 = 6.2k

They foudn that UVLO is working properly with 35V off and 37V on, but OVP is occurring around 57V. Any feedback on the design here?

Vin max = 67Vdc

Vin min = 35Vdc

Vin nominal = 54Vdc

I pointed out that R1 in the typical application was 100k, but the customer was trying to minimize quiescent current over UVLO/OVP accuracy.

When I ran the calculation for R2 I found it should be speced at 6.4kOhm unless I missed a factor of 2 somewhere? Just wanted some feedback on this

over 3 years ago

0 Cameron Perl over 3 years ago

TI__Expert 3990 points

Note I used their R1 value of 200k in that calculation

0 Cameron Perl over 3 years ago in reply to Cameron Perl

TI__Expert 3990 points

Oh darn sorry to keep posting in the thread, but without an edit option I can't correct the fact that I meant to say that was R3 at 6.4kOhm. Which is close to what the customer is using. I forgot that the datasheet calculated R3 prior to R2.

I get R2 = 3.6kOhm and R3 = 6.4kOhm

0 Rakesh over 3 years ago in reply to Cameron Perl

TI__Guru* 95891 points

Hi Cameron,

Can you please share schematic and test waveform of Vin, OVP pin voltage, GATE during OVP test

Best Regards, Rakesh

0 Cameron Perl over 3 years ago in reply to Rakesh

TI__Expert 3990 points

Hi Rakesh,

Thank you for your patience here - I got some additional information.

As using now:

R1 = 200k, R2 = 4.75k, R3 = 5.75k

Gives 32V UVLO, and over 65V OVP (home lab bench supply only goes to 65V so the customer cannot test OVP).

The 32V is close to what was planned/designed so maybe everything is OK now.

Works well shutting off loads up to 59V and about 10A. It is not intended for live load turn-on but it also does 59V/5A (as far as willing to go at home).

The SENSE input resistor is 4.75k and OUT current limit resistor R66 is 3.3k. But have not had the ability to test.