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TPS61200: Unable to configure adequate UVLO threshold for single-cell lithium-polymer input source (3.7V)

Andy Pollock73
Prodigy 100 points
Part Number: TPS61200
Other Parts Discussed in Thread: TPS61230

I am using the TPS61200 (adjustable) reference application circuit on page 14, where I am connecting a single-cell lithium polymer battery (3.7V nominal) as the input supply, and I am setting the regulator (R1, R2) to 4.7V output.  The circuit works fine, but when trying to configure it to use UVLO as a battery saver, it seems unable to be set in a way that makes sense for a 3.7V lithium polymer input source.  I want to set the UVLO threshold for 3V input, which is the recommended lowest battery voltage to allow it to drain down to.  So I have a 249K resistor (R4) to GND from UVLO, and a 2.7M resistor (R3) from Vin to UVLO.  This results in 0.25V at UVLO when the input drops to 3V.   It seems the regulator won't even turn on when I do this, and it may be because at 3.7V input, the voltage at UVLO may not be above the minimum required based on the chip tolerances I see in the datasheet.  I don't see how you can use UVLO reliably to do this for a 3.7V battery and have a reliable 3.0V cutoff, and also make sure it will work if the battery goes above say 3.2V.  What am I missing, or doing wrong here?

  • 0 in reply to Andy Pollock73
    TI__Mastermind 46905 points
    Could you measure the UVLO pin voltage when the input voltage is lower than 3V? make sure the components are well assembled.
  • 0 in reply to Jasper Li
    Prodigy 100 points

    I will do that asap and reply back, but right now, my concerns are:

    1. With the values you see, it won't power on and regulate with a 3.7V input.

    2. When I look at calculated values of UVLO and different Vin levels, and compare to the min and max UVLO thresholds for "lockout" and "unlockout" on falling or rising Vin according to the datasheet, it seems to me that it won't work for Vin nominal of 3.7V and cutoff voltage of 3V.

  • 0 in reply to Jasper Li
    Prodigy 100 points
    OK, we set the input to 3V. UVLO is then measured at 248 mV, using 2.69 Mohm and 249 Kohm, which is correct. Output is 0V, which I understand would be correct. But configured like this, the regulator also won't put out the 4.7V when I power it up with a 3.7V input.
    This is a working regulator at 3.7V input if I don't set the UVLO resistors, and configure it like the standard application circuit not using UVLO.
  • 0 in reply to Jasper Li
    Prodigy 100 points
    So at 3.7V, the nominal input voltage from a lithium polymer single cell battery, we measure 299mv at UVLO. At this input voltage, it does not turn on when setting UVLO as described for 3V cutoff. And I calculate that 299mv is correct for 3.7V. And according to the datasheet, this may not be enough to get it out of undervoltage lockout. So how can it work with a 3V cutoff and a 3.7V nominal input for single-cell Lithium Polymer, which it is supposedly designed to work with? What am I missing?
  • 0 in reply to Andy Pollock73
    TI__Mastermind 46905 points
    the problem is that the 250mV to 350mV hysteresis is too large for this application. because this function is used in low input voltage condition.
    what this the output current requirement for the boost converter. you can have a look TPS61230, which has the similar function for lithium-ion input.