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BQ24079: Question about DPM/DPPM mode of BQ24079

Jeff Zhang22
Prodigy 170 points
Part Number: BQ24079
Other Parts Discussed in Thread: , BQ24072T

Hi,

We are using BQ24079t in a project. we have some issue with DPM or DPPM function of BQ24079. here is my question:

1. the datasheet section 9.3.4.1 (page 19) says  "...When the BAT voltage falls below 3.2V, OUT is clamped to 3.4 V. This allows for proper startup of the system load even with a discharged battery." Unfortunately I do see the voltage at OUT clamped at 3.4V in our design with a fully discharged battery. Our issue is that, the voltage drops to 3V (battery voltage) and the system resets!  So what is the case the OUT voltage clamped at 3.4V? Is it in DPPM mode or Vin-DPM mode?

2. Is the Input DPM mode (Vin-DPM) only available for USB100 and USB500 modes? What about the resistor-programmable mode (EN2=1, EN1=0)?

3. During the testing, we found the voltage on OUT pin drops to battery voltage and last for about 500us. We suspect the BQ24079 get into Battery Supplement Mode. But we didn't see the Vin drops (stay at 5V). How BQ24079 detect the Battery Supplement Mode? by monitoring current only? or voltage?

See below screen shot: CH2 (blue) is the V_IN. CH1 (Yellow) is the V_OUT. 

Btw, we didn't use the USB power as power source. Instead, we use a DC/DC supply.

Thanks,

  • 0
    TI__Mastermind 21590 points

    Hello Jeff,

    1) This only applies to the BQ24072T not the BQ24079T.  In the BQ24079T, VOUT will be regulated to 5.5V if VIN > 5.5V. If VIN < 5.5V, VOUT will be equal to the larger of VIN or VBAT.

    2) The VIN-DPM feature is only available in either USB100 or USB500 mode. However, since the VDPPM is 4.3, the input current is gradually reduced the closer VIN gets to 4.3V to keep OUT voltage above 4.3V.

    3)The device entering and exiting supplement mode is explained below.