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BQ24600: Status pin blinks at 1/2 Hz

John Saunders
Prodigy 165 points
Part Number: BQ24600

I could use some help diagnosing operation of a BQ24600 battery charger IC on our prototype circuit.  We are using it to charge a single-cell Li-Ion battery.  Fully charged set point voltage = 4.2V.  Charge current is set to 0.5A.  Below I included the schematic for the circuit we have on our PCB.

This circuit was working OK for a few days, but for the last few weeks I get the 1/2 Hz error pulse on the STAT output pin almost immediately after powering up the PCB.  I tried 2 different cells, one measured about 3.18V and the other 4.12V.  The charger does the same thing regardless of which battery is connected, even if I manually discharge the 4.12V down to 3.95V, and it also does the same thing if I power up with no battery connected.  The STAT output pulses BEFORE I even drive the CE input high.

I am looking through the data sheet but I can't determine the exact problem.  I measure 3.3V on Vref and about 1.65V on Ts, so I do not think the RTD is too warm.  The voltage on the Vcc pin measures 4.8V.  Can you offer any suggestion as to what might cause this?  I am thinking the key might be that it pulses the output immediately after powerup, before I have CE driven high.

Thank you 

John  

  • 0
    Prodigy 165 points

    Update - Immediately after sending the above, the circuit stopped pulsing and began charging the 3.95V battery at 1/2 Amp (correct).  So this appears to be an intermittent issue.  I was probing the board with a scope lead, so perhaps there is a cold solder joint on the PCB?  Regardless, I would still appreciate clarification on the logic that causes the 1/2 Hz blink on Status.

    Thanks

    John

  • 0 in reply to John Saunders
    TI__Mastermind 24075 points

    Hi John,

       STAT pulsing at 0.5Hz indicates a fault condition. First step would be to run through the possible conditions defined in table 2. of the datasheet. It indicates what events would cause STAT to blink at 0.5Hz for BQ24600.

  • 0 in reply to Kedar Manishankar
    Prodigy 165 points

    Hello Kedar,

    I am aware of Table 2.  At first I didn't think it was very helpful because I couldn't find a clear definition of what "charge suspend" or "timer fault" really meant, but after reading the data sheet more thoroughly I see what they are.  However, I initially don't think I have a problem with charge suspend because the battery is at room temperature (there is no load on it) and I can't have a timer issue because the blinking starts immediately on powerup of the PCB.  So I will have to see what else might be happening.

    On the other hand, I am noticing that even though the Status line blinks immediately on powerup, the last few times the charger starts working after the Charge enable line is driven high a few seconds later.  So the blinking on powerup seems to not be a real problem once I enable charging

  • 0 in reply to John Saunders
    Prodigy 165 points

    Hello Kedar,

    I think that the Vcc we are using is too low.  Also, VREGN may be too low as a consequence.  But I would like clarification on what VREGN should be when VCC = the minimum value = 5V.  Per the data sheet, VREGN = 6V+/- 0.3V at VCC = 10V, but when VCC is lower (5V, the minimum allowed for this IC) what can it be?  It also says the max output current of VREGN = 40mA, but I don't have a way to measure what my circuit sees - so maybe the curent is too high and that pulls down VEGN?

  • 0 in reply to John Saunders
    TI__Mastermind 24075 points

    Hi John,

      REGN is an LDO with VCC as the input, so if VCC is lower than 6V, REGN won't be driven with 6V. It depends on the load on REGN and VCC value, as REGN will be operating in linear mode approaching dropout as opposed to saturation. 

    This part also has a precharge safety timer that is inbuilt at 30 minutes. If you are starting charge when VFB < VLOWV, and in 30 minutes, if VFB does not rise above VLOWV, then a timer fault will be indicated, and charge will stop. Toggling the charge enable pin would reset all timers, so charging could resume again after that.