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BQ25616: how are ILIM, ICHG, and VSET pins implemented?

Brian Bennett1
Prodigy 40 points
Part Number: BQ25616

I am performing a worst case and derating analysis on a circuit that uses BQ25616RTWR. I can't find a description of how the ILIM, ICHG, nor VSET pins are implemented in order to determine if I am meeting the ratings of my pull down resistors. I tried probing the pins and got <1mV on the ILIM and VSET pins; ICHG varied between ~0.25V and ~1V (depending on the type of charger I used).

Can anyone explain how the circuits associated with these pins are implemented and/or what voltages/currents are expected?

  • 0
    TI__Mastermind 23865 points

    Hi Brian, 

    Via the BQ25616 datasheet the absolute max voltage range on the three pins in question are -0.3V to 7V (section 8.1) and the acceptable resistance rating for each pin is as follows. 

    ICHG: ~(225 ohms to 2257 ohms) 

    ILIM ~(149 ohms to 956 ohms) 

    These were found using the acceptable current ranges listed in table 7-1 Pin Functions and the K_ICHG and K_ILIM values found in the electrical characteristics table. 

    VSET:

    Using these acceptable resistance ranges and the max voltage possible on VSET, ICHG, and ILIM you should be able to verify the needed resistor ratings. 

    Best Regards,

    Garrett Kreger 

  • 0 in reply to Garrett Kreger
    Prodigy 40 points

    Hi Garrett,

    I take that absolute max voltage rating to be what the pins can handle (i.e. protection diodes clamping the pins to the rails), not what the pins actually perform to.

    If we assume that 7V max voltage, or even 5V (for the typical  USB rail voltage), then the power dissipated in a 225 Ohm resistor is 5^2 / 225=0.11W. I'm hoping I don't have to use something larger than an 0402 resistor (with a 0.063W limit). 

    Based on my measurements, the pins are not sitting at 5V (which is why I'd really like to know how they work).

  • 0 in reply to Brian Bennett1
    TI__Mastermind 23865 points

    Hi Brian, 

    For this device the exact implementation of these pins cannot be shared publicly. Although I would recommend following the resistor power ratings used on the BQ25616 evaluation module (EVM) as reference on what the pins perform to.

    Here is the link to the EVM user Guide SLUUC73 - BQ25616EVM user guide

    On page 15 you can see all the resistors connected to VSET, ICHG, and ILIM are 0402 resistors rated for 0.063 W, so you should not have to use anything larger. 

    Best Regards,

    Garrett Kreger