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LMZ31707: LMZ31707 UVLO

Khoi Nguyen83
Expert 1180 points
Part Number: LMZ31707

From datasheet table 8, I want to set UVLO at 10V turn-on, and 9.5V turn-off so I select 68.1K/9.31K resistors for Figure 40.

Since my PVIN is from a battery source, I want to limit the leakage current to increase to 681K / 93.1K.

The turn-on voltage seems to work correctly at around 10V, however the turn-off voltage went down to ~7V.

Is this a correct behavior since I don't have the exact equation?

I assume the on/off threshold is around 1.2V typical for INH pin.

Thanks,

Khoi

  • 0
    TI__Guru 50120 points

    Hi Khoi,

    I've attached the equation to calculate the Vstart and Vstop UVLO voltages that is used in the internal controller. Also are you using 1% resistor values? The tolerance of the resistors would affect how well the UVLO start and stop thresholds are set. 

    0 Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Expert 1180 points

    Hi JImmy,

    Let me try with that equation to see if I get the desired UVLO on/off result with higher resistor values.

    I was planning to use 1M pullup and find the pull down value for turning on at 10V and turning off at 9.5V for 3-cell Li-ION battery.

    However, it didn't work correctly so I switched to using the same ratio but x10, which is 681K/93.1K, but then turn-on is at 9.5V, turn-off is 7V

    Yes, I used 1% resistor. 

    Thanks,

    Khoi

  • 0 in reply to Khoi Nguyen83
    TI__Guru 50120 points
    Hi Khoi,

    Please keep me update on this and let me know if this helps.

    Regards,
    Jimmy