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Original question:

BQ25505: Alternative to BQ25505 ultra low-power boost charger

BQ25505: BQ25505 with 1V 100 nA input

Adwaya Sau
Intellectual 550 points
Part Number: BQ25505

With regard to my previous question about the BQ25505, will it still work if I have a 100nA input current at 1V?

  • 0
    TI__Guru**** 157971 points

    Hi Adwaya,

    With a charged storage element >1.8V at BAT, yes.  If VSTOR < 1.8V, in cold start mode, it is unlikely that the inefficient cold start boost converter will be able to raise VSTOR to 1.8V due to the IC's Iq being in the 100nA range.  If it works, it would only work in bursts as the input capacitor charges up, converter operate, stops, repeat.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 550 points

    So if I have a power supply of 2.0V, 100nA, will it be able to charge a supercap (that is initially not charged), from empty to full?

  • 0 in reply to Adwaya Sau
    TI__Guru**** 157971 points

    Adwaya,

    If VSTOR < VSTOR=CHGEN~=1.8V, the charger is in cold start.  Cold start boost circuit is very inefficient boost converter.  It is intended as a last resort.  We do not have efficiency data for cold start operation.  Based on your input power = 200nW, the cold start circuit will have difficultly functioning.  The cold start circuit will likely operate in infrequent bursts as the input capacitor charges above 600mV.  However, the super capacitor and chip dc leakage current, plus any resistive load at VSTOR will prevent the supercapacitor from charging above 1.8V.

    Your 2.0V could be applied directly to VSTOR via a PFET but the chip's Iq is >> 100nA.

    Regards,

    Jeff