• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 1191 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

bq25570 charging Manganese Lithium Coin Batteries

user3928443
Prodigy 60 points
Other Parts Discussed in Thread: BQ25570

Hi,

I´m not very sure if bq25570 can charge Manganese Lithium Coin Batteries (like for example the ML2020).

The charging recommended circuit for this kind of batteries is a 3.1V from Regulator Output (That´s OK for VBAT_OV value), but then you need to limit the current with a series resistor. (See the recommended circuits for charging from this Panasonic Battery). In case of ML2020 you need to limit it to 3mA when battery is at 2.5V and they specify to place a 180 Ohm series resistance between the Reg Output (VSTOR) and the battery itself.

My doubt is that I think that due that the bq25570 charge control is based on voltage values (VBAT_OV), and that you have a series resistor to limit current with the battery, you are always seeing the 3.1V on VSTOR pin, independently of the REAL batt charge status, so you are really not charging OK this kind off batteries, due that the bq25570 will continously enter on Overvoltage detection.

Any Ideas??

Is better to select other chemistry?

Thanks in advance for your ideas.....

  • 0
    TI__Mastermind 20570 points
    VSTOR_OV is a reference voltage set by external resistors. The bq25570 monitors the voltage across the storage element and compares it against the VSTOR_OV threshold.
    The process is illustrated by figure 21. Storage element should be connected to the VBAT pin. When the input voltgae is within the IC's operating range, once the VSTOR pin voltage goes above VBAT_UV plus VBAT_UV_HYST threshold, the VSTOR pin and the VBAT pins are effectively shorted through an internal PMOS FET. Once the voltage on the storage element reaches the VBAT_OV threshold, charging stops to prevent over charging.
    The bq25570 is designed with the flexibility to support a variety of energy storage elements. You can refer to the Typical Application section for examples of different VBAT_OV, VBAT_OK settings for different types of storage elements.
  • 0 in reply to Jing Zou
    Prodigy 60 points
    Dear Jing,

    thanks for your quick answer, but this is not answering my question.

    I´have readed the data sheet and understood (I think) how the storage element is charged. (In my first message I said that is Voltage controlled, like you are explaining in your answer).

    The real problem arises (or I think It will arise) when you need to put a SERIES RESISTOR for there MnLi chemistry Button Batteries (as per Cell Manufacturer Charging Circuit), when the V_BAT pin is not monitoring the Cell, and is really monitoring the Series Resistor plus the cell voltage.

    You can find the charging methods here :

    industrial.panasonic.com/.../AAA4000PE17.pdf

    MnLi manufacturers show that this kind of cell is charged with a constant voltage (3.1V) applied to the the series resistor plus the battery, not directly to the battery, to limit the input current.

    Finally, I have readed the Typical Application section but didn´t found any place where there are typical values referred to chemistry of the batteries. Typical applications sections is providing us with some values for a "battery" with no more specs....

    Finally, I have a circuit draining 200 uA (average).
    Batteries of around 30 mAh will be good enough for me. Any suggestions of a good chemistry choice for this app (I want to supply my circuit with 3V from the buck converter VOUT). Application will charge the battery with solar cells outdoors.

    Thanks in advance
  • 0 in reply to user3928443
    TI__Mastermind 20570 points
    The bq25570 can be used to charge MnLi coin cell battery. The voltage on VBAT will raise to VBAT_OV and regulated to VBAT_OV. In your case, you can set the VBAT_OV to 3.1V according to the ML2020 datasheet and use the seris resistor to limit the current. However, the charge time will be extended. Battery cell will eventually charge up tp 3.1V.