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BQ51050B: Is it possible to limit the charge current to 200 mA?

Part Number: BQ51050B
Other Parts Discussed in Thread: BQ51013B, BQ51052B

We developed a circuit with the BQ51050B and it works. It is built with the examples from the datasheet, R1=110 ohm and Rfod=200 ohm (with the typical application schematic, R1 from ILIM to FOD, and Rfod from Rfod to GND). This results in Ibulk of 1 A. But we are planning to use the Varta EasyPack S, see here.

The maximum allowed charging current for the battery is 650 mA. But for a longer battery life, we plan to charge it with 200 mA. Is this possible with the BQ51050B and which values should I use for R1 and Rfod then? If it is not possible, which would be the lowest possible charging current and which are the values for R1 and Rfod? And what would be the recommended value for Rterm?

  • HI Frank,

    The device is characterized as having a charge current range from 500 to 1500 mA. For resistor values, this puts you at a R1 + Rfod value of a minimum of 628Ω (based on KILIM = 314 AΩ). We recommend 200 Ω as a starting Rfod value before FOD calibration.

    Rterm value is a design configuration. Based on the EasyPack S datasheet, the recommended charge cutoff is 6.3mA. This value would translate to a Rterm value of  302Ω (which is  1.26%).

    These were calculated with the following equations found in the datasheet:

  • Thanks for the information. Would you say based on your experience that it reduces the life time of the battery a lot when it is charged near the maximum allowed continuous current? And is there a pin compatible drop-in replacement of the chip which allows a lower charge current?

  • Hi Frank,

    The BQ51013B is a potential solution. It is pin to pin except for the TERM pin on the BQ51050B is switched with an EN1 pin on the BQ51013B. The EN1 is an input that allows for enabling/disabling wireless or wired charging. 

  • Hi TI,

    I am a user of the BQ51050b, too, and just want to understand the problem.

    I tried charging a LiIon accu with a bulk current of about (just) 150mA and selected a corresponding RLim.

    It seems to work great.

    On page 11 of the datasheet there is a diagramm for a 300mA fast charge efficiency ??

    So 300mA is possible and allowed ?

    What could be the bad consequences when chosing bulk currents below 500mA ( as the minimum bulk current in the operating conditions is mentioned) ?

    Thank you in advance

    i2e / Rolf Molitor

  • Hi Rolf,

    We do not guarantee operation or efficiency beyond the datasheet. The figures you are referring to pertain to the BQ51052B are showing efficiency in fast charge vs taper charge.

  • Hi Anthony,

    but doesn't the figure 7 in the datasheet show a 300mA fast charge ?

    And the BQ51052 is limited to 500mA as lowest current as well as the BQ51050..

    In another post regarding the BQ51050B it is said, that the real problem would be the termination accuracy.?

    The termination current, which for instance is selected as 10% of the bulk current should not be under 30mA ?

    So, does this mean, that when i select 200mA as bulk and 10% of that as termination, it is not guaranteed that the termination really happens at 20mA, but maybe at 25mA or 15mA ?

    Thank you and best regards

    i2e / Rolf Molitor

  • Hi Rolf,

    Yes, as you've mentioned, the termination would be a concern in terms of accuracy and yes termination is set to 10% with 200mA as bulk, the 20mA would not be guaranteed.