This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24725A: REGN current limit

Part Number: BQ24725A

Dear expert,

My customer is evaluating BQ24725A. Thier circuit diagram design is similar to the following figure in the datasheet.

The logic for the Buck circuit of 24725A is turning on REGN to charge capacitor C7 through diode D1. Now the problem is that the current through D1 is large(reach to 2.16A,  may be drawing current from an external 1uF capacitor) when the Q4 is turned on first, the duration is 128ns. And customer use the diode D1 specification IFSM: 0.6A, time 1s, datasheet didn't define the current-time curve.

So the first question is whether they choose the right diode or they need to improve the design?

The second question is about REGN's current limit. The typ value of the current limit of REGN 75mA defines the peak value or average value? If the Load of REGN exceeds this value, how is the LDO inside REGN protected? Will it shut down the LDO output? Thanks for your support.

CH1: Phase to ground   CH2:REGN to ground   CH4:D1 forward current

  • Hi Minqi,

    BQ24725A EVM BOM would be a good reference. A 600mA Schottky diode should be good if the voltage rating is enough.  

    The REGN current is DC average current. When the pulsing current to charge the BTST cap, the REGN cap is the main source as RGEN cap is about 20x of the BTST cap.

  • Hi Eric,

    Thank you. Just to make sure, if the load is too large for REGN LDO, what will the REGN current limit react? Will it shut the output down or lower the output? Thanks. 

  • Hi Minqi,

    When the REGN current limit is exceeded, the REGN output will shut down.

    Please see the waveform below for my test on a BQ24725A EVM. I slowly stepped up the REGN load current from 75 mA to 80 mA in 1 mA steps. At IREGN = 80 mA, the REGN current limit was exceeded, and VREGN fell to 0 V.

    At this point, the ChargeCurrent() and ChargeVoltage() registers were reset to zero, thus disabling charging. With charge disabled, the typical value for the REGN current limit is 14 mA, which is similar to what I see in the waveform (IREGN = 17 mA after charge is disabled).

    Best regards,

    Angelo