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Active power management, 50mA battery charge current and 4.1V batt voltage - not an option?!

Other Parts Discussed in Thread: BQ24072, BQ24031, BQ24079, BQ24060

I am looking for an IC that can do active power management (most important function is load switch from the battery to the external supply), and can allow a battery charge rate of 50mA for a 4.1V LiIon (thus Vbatt charge threshold needs to be 4.1V). Plus have a system Vout of less than 5V, preferably 4.5V or less.

I have had a look at all various versions in the BQ series that have Active Power Management, but just could not find anything that suits (in particular none of these allows a 50mA charge rate).

Is there something I missed? In case the answer is No, are any of the relevant ones in the BQ series customisable? For example the BQ24072 would be perfect, but regulates Vbatt only at 4.2V (and not 4.1V) and it looks it doesn't allow a charge rate lower than 90 to 100mA (for USB mode only).

Other potentially suitable ICs would be BQ24031 or BQ24079 but: is the Vout reg customisable to 4.4V, and can any of them work with 50mA batt charge current, etc.

In case that the answers above are all No, the first feature to drop would be the Active Power Management feature: in this case I found only one IC in the BQ series that looks it should work down to 50mA battery charge rate, which is BQ24060 (at least from the characterisation plots it should - see Fig 8 for "Low Charge Rate" and 10, but not from the specs, which specify the minimum charge rate as 100mA) and given that it has a separate Bat input, one could use a resistive divider there to change the batt recharge voltage from 4.2 to 4.1? Again, is the 50mA charge rate correct (as shown in the plots), and could I use a resistive divider to set the Vbat at 4.1V?

Sorry for the long message but this exercise turned out to be quite frustrating (and long), and I need a solution quite fast.

Regards,

Edmond

  • The parts you mention above all have an ISET pin.  At charge currents below 100mA, the accuracy suffers as you can see by the K(ISET) specificaiton in the datasheet's electrical specs tables but, even if we haven't tested for charge currents below 100mA, you could still set the current to 50mA.

    The best fit may be bq24031, using the USB input only and pre-regulating your input voltage down to the voltage that you want using a linear regulator IC.  The bq24031 passes through the USB voltage to the output.

     

     

  • Hi Jeff,

    Thanks. In the meantime I ordered the Dev kits for both 24031 and 24079.

    One or two questions re your reply above: you recommended to use the USB input.

    But it looks to me that what I can do is to choose Psel = Low (ie, USB charging is default), set Iset2 = Low, and apply Vin on the AC input - this extends down the spec'ed charging rate to 80mA (min). See note 12 on page 5 of the 24031 spec sheet. And, same as for the USB case, if the Vin on the AC input is below Vo(out-reg) value (which is ~6.3V), than Vin is passed out unregulated on Vout (same as for the USB input).

    The reason to use the AC input is a lower Iset2 'low level input current' (-20uA, worst case) compared to the 'high level input current' (40uA worst case), and possibly the same for Psel currents (note that the 'high level input current for Psel is not shown in the spec, pg6). 

    Also there is a reason to choose 24079 over 24031, given that one can use the value of the voltage developed on the Iset pin as a direct reading of the batt charging / and discharging current; seems to me that one cannot use the Iset1 pin of 24031 to implement the same function (am I correct)?

    The drawback is that in 24079 case, Vdppm is fixed, while in 24031 Vdppm can be set to arbitrary values.

    And finally, you mentioned accuracy loss following setting a 50mA charge rate: the question is which parameters are affected (charging current, charging voltage, any timing parameters, etc)?

    Regards,

    Edmond

  • Regarding the 80mA, that is the input current limit specification not charge current.  The charge current is the lower of the input current limit or charge current per the Iset pin.

    Regarding the Iset pin voltage, it is a direct reading of the charging current only, not the discharging current.  The Iset pin has no relationship to the discharging current.

    Regarding the accuracy loss, the charging current will not be as accurate below the tested range.