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Require charger recommendation

Jonathan Reid87
Prodigy 50 points
Other Parts Discussed in Thread: BQ25120A, BQ24259, TLV713P, BQ24195

We need to add a charger to our product

  • 1x Li Ion cell
  • 5v input
  • 3.3V, 50mA min output for BLE IC
  • 3.8V nom output for SIM7000E LTE module

There are lots of options if use a charger IC + 3.3V LDO + buck/boost regulator for SIM7000E.

Is there a single IC option or other minimum component option available ?

The max input voltage for the SIM7000E is 4.3V so when the 5V input is connected the SYS voltage needs to be < 4.3V

It would be ideal if as battery voltage drops SYS voltage is maintained at say above 3.5V

  • 0
    TI__Guru**** 167196 points
    Jonathan,

    What is the capacity (maximum charge current) for the LiIon cell?
  • 0
    TI__Intellectual 1640 points
    Hello Jonathan,
    The BQ25120A integrates buck regulator and an LDO/LS. It's an I2C charger, the Max programmable Vsys is 3.3V, and the max programmable LDO voltage is 3.3V. The battery regulation voltage is programmable from 3.6-4.65V. The maximum charging current is 300mA. This charger has ship mode with ultra low Iq of 2nA in ship mode, and it also has ultra low termination current down to 0.5mA.
  • 0 in reply to Jeff F
    Prodigy 50 points

    It is a protected MCR18650B 3200mAH.  Max recommended charging is at 1.6A

  • 0 in reply to Upal Patel
    Prodigy 50 points
    I am not sure that is best for us as the output current is too low. When transmitting in GSM mode (which we may use) the SIM7000E will draw 2A bursts on a 13% duty cycle. Also the package is a bit tricky to deal with for us in small quantities
  • 0
    Prodigy 50 points
    Currently I am thinking of a 2 chip solution bq24259 + TLV713P (or similar)

    The bq24259 will have SYS range of 3.5-4.35V
    The SIM7000E supply range is 3.0-4.3V (so will use low forward voltage diode after SYS output)
    The nRF58232 BLE will operate down to 1.8V so can run LDO off SYS no problem

    Any issues with this plan ?
  • 0 in reply to Jonathan Reid87
    TI__Mastermind 25800 points

    Hey Jonathan,

    I do not think I saw it asked, but will the input ever be removed such that only the battery will be the only source of power?

    If not, I do not see any issues with what you are trying to do.

    However, if the battery is the only power source, keep in mind that Li-ion cells like the one you are using can typically go down to 2.5V (with a protection circuit) or lower (without protection circuitry). In this "battery only mode", the SYS voltage will track with the battery voltage. Then add the additional voltage drop from the diode and you could find yourself a bit under-voltage for your devices.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 50 points

    I do require the unit to run off battery only when the power is temporarily off

    My understanding is that if boost mode is enabled (OTG high) then the output will not track the battery voltage but be minimum 3.5V (default, but can be configured)

    I can see both the Arduino MKR 1400 and Particle Electron using the BQ24195 in this mode (I am assuming the BQ24259 works the same.

    Or have I missed something here ?

    https://content.arduino.cc/assets/MKRGSM1400-schematic.pdf
    docs.particle.io/.../

  • 0 in reply to Jonathan Reid87
    TI__Mastermind 25800 points

    Hey Jonathan,

    The boost mode on this charger and others that offer the OTG mode only regulate the voltage at PMID/VBUS, not at VSYS.

    VSYS is only regulated when there is an adapter present. In battery only mode, the BAT pin, and subsequently through the Q4 BATFET, the SYS pin are the inputs to the boost converter. Essentially, to allow OTG to function, we utilize the same buck converter used when charging with an input source and operate it in reverse direction.

    As far as the schematic you linked from Arduino, at first glance I can only assume that they are using the OTG output somewhere else because the +5V line is only connected to a jumper and the USB connector. That rail reconnects to the VBUS pin of the charger which technically would have no effect. I am also assuming that they have some voltage monitoring/supervisor circuit to tell them when the battery their supply rail or the battery voltage is getting too low.

    In summary, in charge mode (with an external input applied to VBUS), VSYS is regulated to 3.5V and will track with the battery voltage as it rises above that threshold. In BAT only mode, the SYS voltage will be an I*RDSon drop below the Battery voltage.

    Regards,

    Joel H