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LM3421-Q1: Inquiries about OVP

MJ Jeon
Genius 5240 points
Part Number: LM3421-Q1
Other Parts Discussed in Thread: LM3421

Hi, TI Support Team

OVP is not working properly.

Please review the contents below.

Applicaton: LOWBEAM HEADLAMP

TOPOLOGY: BUCK-BOOST

VIN : 10~36V

VLED: 17V

ILED: 1A

OVP TARGET: VIN + VLED: 17 + 36 +2V (margin) = 55V

Even if I changed ROV1 and changed from 549K which is TARGET to 432K, it did not enter.

It is implemented in the way of FLOATING OVP, and OVP does not enter the 2HZ specified on the data sheet.

There seems to be a part in our circuit that needs debugging, so please review it.

OVP_CIRCUIT_LM3421.pdf

Thanks.

Regards,

MJ

  • 0
    TI__Mastermind 18890 points

    Hello MJ,

    Note that the OVP protection voltage is the voltage across the LED only and not the voltage of the LED plus VIN as you have in your design of 55V.  So for your design you should use design OVP to be about 3V above your maximum LED voltage which is 3V + 17V = 20V.  Then follow equation 24 and 25 of the data sheet to calculate your set point and hysteresis design value for the floating case.

    Thanks Tuan