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LMR70503 VEN Divider

Hirotsugu Kobayashi
Mastermind 8885 points
Other Parts Discussed in Thread: LMR70503

A datasheet has the following statement.

It is important to ensure that a valid input voltage (2.8 V ≤ VIN≤ 5.5 V) is present on the VIN pin before the EN input is asserted.

The demo board is a resistor divider to pull EN pin up to half Vin.

So the IC will be enabled when VIN is higher than UVLO(typ 2.55V), but EN pin is 1.275V then.

I think EN pin is asserted before VIN reached a valid input voltage.

Doesn't this become a problem?

Please tell me the correct divider value in the case of 3.3Vin?

  • 0
    TI__Genius 11085 points

    The key point of that statement on the datasheet is to make sure EN is not going to have a higher voltage than VIN, ever.

    VEN > VIN could damage the LMR70503.

    VEN passes threshold sooner than VIN passes UVLO presents no risk to the IC. It is safe to tie EN through a resistor divider to VIN.

    The divider for 3.3Vin depends on the enabling level you want to set by EN.

    Hope this helps.

    Yang