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bq2403x or bq2407x

Gokhan Yenikaya
Prodigy 40 points
Other Parts Discussed in Thread: TPS63020

I am working on a design that I'll use bq2403x or bq2407x in my design. Reading the datasheets I confused a bit. In the presence of AC adapter input or USB input (or both) the devices output a regulated voltage of 4.4 V or 6 V. When there is a problem about the input sources, the DPPM sustains the regulated voltage with the support of the batteries at the defined voltage levels (4.4 V or 6 V). But I could'nt exactly understand, or could not see in the datasheets the case of absence of the both input sources. In the absence of the input sources (both AC and USB are absent, there is only battery), will the DPPM keep the regulated voltage at 4.4 V or 6 V levels? Or will the output voltage tracks the voltage of the battery?

  • 0
    TI__Guru*** 148790 points

    The IC has 2 means to maintain the output voltage.  The first is by reducing the charging current, if the output voltage drops below the DPPM setpoint.  The battery is still being charged, but with a reduced current.  The output voltage is maintained at the DPPM setpoint.

    If the output voltage drops further, the IC further reduces the charging current.  Once the charge current reaches 0, the output voltage drops to just below the battery voltage.  Now, we are in battery supplement mode.  Both the input source and the battery are supplying the output--the battery is being discharged.

    If there is no input source, the output voltage will be slightly below the battery voltage.  It will not be at 4.4V or 6V, as there is no means to boost the battery voltage in the IC.

  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Thanks,

    but could you give an idea about this, the IC will feed a system of 3,6 - 4,2 voltage range with a peak current of 2 A, in average 500 mA. Should I use a buck/boost regulator or any other?

  • 0 in reply to Gokhan Yenikaya
    TI__Guru*** 148790 points

    Yes, if this directly feeds a system that requires an input range of 3.6-4.2V, then you need to match this input range to the output range of the charger which can go from the lowest battery voltage (usually around 3V) to the Vout setpoint (of 4.4V or 6V).

    With a 2A load, the TPS63020 would be the buck boost that meets your needs.