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Original question:

TPS2115A: Power mux between 4 batteries that may not be present

TPS2117: Power mux, two parallel batteries. Recommended device.

PMRC
Prodigy 30 points
Part Number: TPS2117
Other Parts Discussed in Thread: TPS2113, TPS2216, TPS2121, TPS2115A

Hi

The system is powered by two Li-Ion batteries. The power consumption of the load is around 1-1.5W.

The ideal mode should be the diode mode so that the battery with the highest voltage is active. It will work in standalone mode.

However, the datasheet (page 11) suggests not using that mode for this configuration:" It is not recommended to use diode operation for two inputs of the same voltage, that is when the device is to multiplex and to connect one input channel to the output. "

Why is it not recommended?

Are there any other suggested devices or configurations?

During the crossover between batteries, the load should continue working. Is it necessary to add a large output capacitor to avoid dropout during the change between channels?

Thanks

  • 0
    TI__Mastermind 23740 points

    Hi PMRC,

    This recommendation is present because this will cause repeated switching between batteries when they're at the same voltage. This can be worsened by higher currents when the load step response causes batteries' voltages to dip, and in serious cases this can cause the output to drop below the downstream component's UVLO voltage. However, there is 60mV of hysteresis when in diode mode, so if you find that there is not excessive oscillation in this mode then it's fine to use.

    What's typically recommended if the device causes issues due to repeatedly switching between inputs is to use the priority mode (MODE = high, resistor divider from VIN1 to PR1) - this will use the first battery exclusively until it discharges to a resistor-programmed voltage, then use the second battery exclusively until PR1 goes above the threshold again. However, this will increase Iq.

    The switchover times are pretty quick at around 15us, so at low currents minimal holdup capacitance is needed, maybe 1-10uF if your load doesn't already have capacitance.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 30 points

    Thanks for your reply.

    In the past, we tested the TPS2213, but it wasn't suitable, so I assume the TPS2117 wont' be also suitable in our application.

    We can't use the priority mode because then the battery monitor won't work properly (we only have one input to the main board, so it will show, for example, that the battery life is 25% when the second battery is still full).

    Do you have some alternative with higher level of hysteresis?

  • 0 in reply to PMRC
    TI__Mastermind 23740 points

    Hi PMRC,

    Do you mean TPS2113? I'm finding a TPS2216 but not TPS2213.

    Understood about priority mode not being an option. There's also TPS2121 which has a much higher hysteresis of about 300mV typ, but has an Iq of about 300uA. TPS2115A has a hysteresis and Iq between TPS2117 and TPS2121, if neither of those work.

    Would any of those work?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 30 points

    Hi, TPS2113APW, https://www.ti.com/product/TPS2113A/part-details/TPS2113APW

    I'll take a look to your suggested alternatives! thanks

  • 0 in reply to PMRC
    TI__Mastermind 23740 points

    Hi PMRC,

    Great, please let me know any additional questions you have!

    Thanks,

    Patrick