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BQ24210: Maximum allowed pullup resistor for /PG when tied to /EN

Attila Eredics
Prodigy 195 points
Part Number: BQ24210

Dear TI Experts,

I design a solar charger circuit with a 6V/1W solar panel for a ~2000 mAh Li-ion battery.

Based on Fig. 13 Typical Application Schematic (on page 20 of SLUSA76B), I want to:

- use LPCM, therefore connect TS to VTSB (no thermistor)

- use battery tracking mode, therefore leave VDPM floating

- enable auto charging, thus connect /PG to /EN

- but I don't need LED or any status indication for the MCU

Since /PG is open drain, I'll still need a pullup to VBAT (e2e.ti.com/.../1991028, but I don't want to waste energy here. So my questions:

1. what is the maximum allowed pullup resistor value, taking into account the combined leakage currents of /PG and /EN, and also not violating the voltage thresholds of /EN?

2. how will a high value pullup resistor affect the noise immunity of the circuit (a GSM module is also onboard)? How can I improve it, if necessary?

Thank you very much for your help!

  • 0
    TI__Guru* 75906 points
    It is very hard to predict what maximum pull up would work in your application, evaluation will need to be done on the design against design requirements.

    But if we only look at the info in electrical characteristics table:
    1.) The /EN pin logic high is listed as 1.4V min and source current listed as 2uA max.
    2.) The /PG pin leakage current is 1uA max
    3.) If the pull up voltage is Battery ( ~3V)
    Pull up in the range of 500k ohm could be used as a starting point for evaluation.

    Note that I-OUT Quiescent Current (battery leakage) is 5uA max, with /EN high.

    Noise immunity is hard to predict and will need to be investigated on your specific design and noise environment. Often filtering capacitors can be added to logic lines. With this high a pull up resistor transition time from low to high may be a problem, time required to charge the capacitor.
  • 0 in reply to Bill Johns
    Prodigy 195 points
    Thank you, I'll try these as soon as my components arrive.