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Original question:

BQ25570: Output current of boost circuit/Overcharge and overdischarge protection

BQ25570: design a system that has periodic 500mA current

zhaozhuo li
Prodigy 10 points
Part Number: BQ25570
Other Parts Discussed in Thread: BQ25505

Power input:  1V, 20mA average

Power storage: 500mAh Li-poly battery, rechargeble

Desired Power output:  3.3V, peak 500mA (may last 5ms),  average 1mA.

Can bq25570 supply 500mA peak for short time? 

From spec page 17:  "The converter delivers an output current up to 110mA typical".

yet page 24 has show an example to output 500mA with enlarged Cstor.

Could you help clarify whether and how can I achieve the desired output?

And if not feasible with BQ25570, will any other chip like bq25505 can fulfill?

  • 0
    Prodigy 10 points
    per another thread in E2E "BQ25570: Drawing current directly from a lipo connected to VBAT",  @Jeff F mentioned "it's OK to run the radio from battery".
    Could you elaborate a bit whether this can be achieved with the design as in the Typical Application Circuit in spec?
    Or shall we need to connect the radio loading to the "VBAT" ?  (rather than "Vout" as in the Typical Application)

  • 0
    TI__Guru*** 143950 points

    Hi,

    Since your output power transient of 3.3V*0.5A = 1.65W is greater than your input source power of 1V*0.02A = 20mW, your load will have to rely on the battery.  If you need the undervoltage protection from the internal PFET between VSTOR and VBAT, with your load connected at VSTOR, the almost 1 ohm resistor will cause with a 0.5V drop from VBAT to VSTOR during the transient.  If your battery has internal undervoltage protection, you can short VSTOR=VBAT.  Also, the frequency of the transient may be an issue.  I suggest using the design example at the link below in order to determine whether the transient is infrequent enough for your input source to charge the battery and/or if the battery is large enough.  

    https://www.ti.com/lit/zip/sluc461

    There are a few boost converter ICs (like TPS610986) that can operate below 1V but their switch current limit is quite high and will collapse the 20mA input source because they do not offer input MPPT.

    Regards,

    Jeff