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LM5116: About the resistor value used for EN pin and UVLO pin

Kaji@PAN
Mastermind 7350 points
Part Number: LM5116

Hi,

I am verifying off-sequence of a circuit using LM5116.
The circuit diagram around the device is shown below. VOUT is 17V.
If the 8V regulator stops operating when 12V is off during the off sequence, 12V will not be discharged.
Therefore, EN and UVLO take a long time to reach the low threshold and take time to turn off VOUT.

The following measures were implemented as the measures above.
1.UVLO pin: pull up 10kohm and pull down 1.8kohm
2.EN pin: 100kohm pull-up and 100kohm pull-down

I use a low resistance value to increase the amount of discharge so that 12V drops quickly, but the discharge function is not enough and I would like to consider further reducing the resistance value.
How low can the resistance used for EN and UVLO be reduced?

Best regards,

  • 0
    TI__Mastermind 27130 points

    Hi

    pls corrent me if I understand wrong. you want to turn off LM5116 quickly after your 12V aux bias is off. but 12V aux voltage discharging very slow which make the LM5116 output voltage dropdown very late after 12V aux off, right?

    if I understand is right, can I ask where is the signal for 12V off,is it can be used for turn off the LM5116 after certain delay time?

    thanks

  • 0 in reply to Daniel Li14
    Mastermind 7350 points

    Thank you for your reply.
    >you want to turn off LM5116 quickly after your 12V aux bias is off.
    >but 12V aux voltage discharging very slow which make the LM5116
    >output voltage dropdown very late after 12V aux off, right?
    Yes,your understanding is good.
    I want to discharge the 12V charge quickly using a resistor connected to EN and UVLO.

    >if I understand is right, can I ask where is the signal for 12V off,
    >is it can be used for turn off the LM5116 after certain delay time?
    12V is made separately on the same board. It is difficult to change the timing of this 12V off.

    Again, is there a limit on the resistance connected to EN and UVLO?

    Best regards,

  • 0 in reply to Kaji@PAN
    TI__Mastermind 27130 points

    Hi

    there is no limitation for resistor you used in EN and UVLO.  

    only pay attention of the resistor's power loss when you used small value.

    Thanks