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Overdriving the output of the TPS72728 LDO from the USB LDO in a MSP430F5528

gary parrett
Prodigy 40 points
Other Parts Discussed in Thread: MSP430F5528

I have a battery powered board in which the normal power mode is a 3.6V Li ion battery through a TPS72728 LDO providing 2.8V attached to the DVCC and AVCC power pins. The product has the ability to be stored with the LDO turned off so that minimal current is drawn. When we need to use the product it is plugged into USB and we use the USB LDO in the MSP430F5528 to provide the power to DVCC and AVCC to start the application. I have a diode in series with VUSB to protect the USB LDO. While in USB mode the 2.8V LDO is turned on.

My question is are there any issues with overdriving the voltage on the 2.8V LDO from the USB LDO? It is working with the current design I have but I want to make sure that this will work across the range of USB LDO voltages which goes up to 3.6V. I am currently seeing 3.3V at the output of the LDO with a drop across my diode down to 2.9V.

Thanks,

Gary Parrett

 

  • 0
    TI__Expert 8890 points

     

    Hello Gary,

    "Overdriving" the output of the LDO will serve to turn-off the pass-FET of the LDO - which is exactly what you want to do in this application. What you are doing will work well as long as  the voltage at the output of the LDO is not above the output of the battery. If the battery voltage falls below the voltage at the output of the LDO then a reverse current will flow through the body diode of the LDO's pass-FET into the battery - possibly shorting out the USB LDO.

    Regards

    Bill