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Device entering DPPM MOde (bq24073)

Diane Eaker
Prodigy 100 points
Other Parts Discussed in Thread: BQ24073

We are using the bq24073 and I don't understand why the unit is enetering DPPM mode.  ILIM is 1.18K and ISET = 1.02K.  According to my calculations, the unit should allow a combined (load + charging) load of ~1.36 Amps.  I have my system set up for fast charge current of 0.87 A.  My max load is no more than 300mA (more like 265mA) and when the unit has a fully depeleted battery, I see the power supply draw 0.87 Amps which makes sense.  Then, when I power the load on, I would expect to see if jump to 0.87 + 0.3 = 1.17 A which is within the ILIM setting.  But, I don't.  The current draw remains at 0.87 meaning the system is reducing the charge current because of the load and DPPM being evoked.  When I measure Vout, it is ~4.35 V while charging w/o load.  When I power the load on, that drops to 4.2839V which causes DPPM to kick in since DPPM kicks in at 4.3V on the bq24073 according to the datasheet.  I am confused.  My power supply current limit is 3A so it can not be a supply issue.  Why is the Vout dropping to 4.2839 thus invoking DPPM?  I don't understand it based on what I am reading from the datasheet.  Any ideas?

Diane

  • 0
    TI__Guru**** 166996 points

    Is the IC hot to the touch?  Perhaps you are entering the IC's thermal protection loop and it is what is limiting the dharge current.  What is the IN voltage at the IN pins?  Perhaps the VINDPM loops is limiting the charge current.

  • 0 in reply to Jeff F
    Prodigy 100 points

    The IC is not hot.  Vin is 5V.  As a note, I "upped" my Vin to 6.5V and my current draw went up above the 870mA (it hit something like 970mA).  However, the chip was getting pretty toasty so I shut down the power supply.  So, what does this mean exactly?

  • 0 in reply to Diane Eaker
    TI__Guru**** 166996 points

    When you upped your Vin, was the 6.5V measured at the IC pins or from the supply?  You could have a voltage drop across the leads from your power supply to the IC.  Have you tried loading the OUT pin with the charge current disabled using /CE?  How much load current can you get in that configuration? 

  • 0 in reply to Jeff F
    Prodigy 100 points

    Good catch, the 6.5V was my power supply digital reading.  When I measured at the IN pin of the bq2073 I am seeing about 0.4V less than what the power supply reports.  I need to look into this further.