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BQ25570: Back power VOUT while programming MSP430 load?

Part Number: BQ25570

My system is a BQ25570 powering a MSP430 at 2.6V.  The MSP430 is on the regulated VOUT net of the BQ25570 (on the buck step-down).  Storage is a supercap on VBAT, charged to max of Vbat_ov of 5.4V.

I want to program (burn) the MSP430 using a debugger probe at 3.3V.  Can I connect the debugger probe to the VOUT net and back power the buck converter, without harm?

I suppose I can choose a VOUT regulation voltage of 3.3V instead, would that work?

I suppose I can use a jumper to isolate the MSP430 while programming it.

  • Lloyd,

    I will have to test and then confirm with design whether you can safely apply higher than VOUT voltage to BQ25570 buck. 

    Changing the VOUT regulation point on the fly is possible by switching in a different feedback resistor.

    Regards,

    Jeff

  • Hi Lloyd,

    I tested on the bench and do not see any issues with a VOUT being prebiased to a voltage higher than VOUT regulation point at start up.  There is a small leakage path from VOUT to VSTOR if the applied voltage is higher than VSTOR voltage so I do not recommend applying than VSTOR to VOUT.

    Regards,
    Jeff

  • Thanks.  The problem is that I can't guarantee Vstor has any particular value.  Typically the board has just been assembled and due to ambient light the solar cell and BQ might have started charging, at the time that I connect the debug probe to do in-circuit programming of the MSP430.  I suppose I could just change my process, and fully charge storage before programming.  Or use a diode or a jumper.