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TPS54326 – About behavior at low Vcc (out of recommended range)

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Guru 21045 points
Other Parts Discussed in Thread: TPS54326, TPS54226

Hi Team,

 

My customer would like to use the following condition.

We understood that this condition is not recommended.

However, my customer would like to know about behavior at low Vcc (out of recommended range).

Could you please let me ask the following question?

 

<Condition>

-Vcc and Vin = 6.0V to 8.4V (2cell battery)

-Vout=1.15V

-Iout= 1.5A(max)

 

*Vcc and Vin are 6.0V to 8.4V(2cell battery).

However, they may drop to 4.08V (between 10ms and 20ms).

 

 

 

---------------------

[Q1]

Does TPS54326 stop the operation when Vcc become 4.08V?

I guess that TPS54226 don't stop because Vcc is higher than “UVLO=3.05V(max)”.

Is my understanding correct?

--------

 

[Q2]

Is there the matter other than the operation stop when Vcc become 4.08V?

 

For example, I think that the internal Vreg5 regulator don’t regulate for internal MOSFET Drivers.

Therefore, the on resistance of internal MOSFETs(RDS(on)h and RDS(on)l) will be higher than the value which is mentioned in datasheet

Is my understanding correct?

---------------------

 

Regards,

Kanemaru

  • 0
    TI__Guru**** 191445 points

    The UVLO operates from VREG5 not VIn.  If VREG5 drops out of regulation the device will shut down and latch off until EN is cycled.  The UVLO shut down voltage for VREG5 can be as high as 3.82 V.  I ma not sure about the internal headroom of VREG5 relative to VIN.  I can probably get you typical only not worst case.

    Yes when VREG5 is reduced, the drive to the internal FETs is lessened.

    I think in your case you are operating very close to the operational limit.

  • 0 in reply to JohnTucker
    Guru 21045 points

    Hi John-san,

     

    Thank you for your prompt reply.

    Could you please let me know about value of the internal headroom of VREG5 relative to VIN?

    And, If TPS54326 is the following states, does “the on resistance of internal MOSFET” increase?

     

    > Yes when VREG5 is reduced, the drive to the internal FETs is lessened.

     

    Regards,

    Kanemaru