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Original question:

BQ25895: BQ25895 boost converter output

BQ25895: Boost Mode : Output current limited

Piyush Charpe
Prodigy 30 points
Part Number: BQ25895


Hello all,

I am facing a problem with the Boost Mode of BQ25895 IC. IC is unable to provide current more than 1 Amp in boost mode whereas
in normal mode, It provides current as per externally connected load.

Case 1: Without boost mode
1. Input voltage (VBUS): 5.5v
2. VBAT: 3.8v
3. Output voltage (PMID) : 5.4v
4. Load current: 2A

Note: BMS works properly in this mode. With an increase in input voltage (VBUS) output voltage (PMID) also increases and it is delivering current properly as per load connected.

Register Map :

       0    1   2   3   4   5   6   7   8   9  a    b   c    d   e   f 
00: 7f   05 3d 3a 20 13 5e 9d 03 44 93 76 80 19 00 00
10: 00  9e 00 1c 39  ff   ff   ff   ff   ff   ff   ff   ff    ff   ff   ff


Case 2: With boost mode (Output current up to 1A)
1. Input voltage (VBUS): 5.5V
2. VBAT: 3.8v
3. Output voltage (PMID) : 5.48v (Set to 5.5v by configuring REG0A)
4. Load Current : 1000mA

Note: Boost mode works properly till the time output current is less than 1000mA.

Register Map :

       0   1   2   3   4   5   6   7   8   9   a   b   c   d   e    f 
00: 7f  05 3d 3a 20 13 5e 9d 03 44 93 e2 80 19 00 00 
10: 00 1e 00 3f  39  ff   ff   ff   ff   ff   ff   ff   ff   ff   ff   ff 


Case 3 : With boost mode (Output current > 1A)
1. Input voltage (VBUS): 5.5V
2. VBAT: 3.8v
3. Output voltage (PMID) : 0v

Note :
1. As soon as the load starts draining current more than 1000mA boost mode output drops to 0v.

Register Map :

       0   1   2   3  4    5   6   7   8   9   a   b   c   d   e   f 
00: 7f  05 3d 3a 20 13 5e 9d 03 64 93 02 c0 19 00 00 
10: 00 1e 00 3f  39  ff   ff   ff   ff   ff   ff   ff   ff   ff   ff   ff

Please let me know why IC is not allowing the current more than 1000mA.

  • 0
    TI__Guru 57651 points

    Hi,

    REG0C shows boost fault. Are you testing with real battery or battery simulator?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 30 points

    Hi Ning T,

    Thanks for your response.

    We did the test using a

    1.  Li-Ion battery ( Part No- "Samsung 18650", Ratings-  2600mAh, 2C ).

    2.  Battery simulator

    In both cases, it is observed that

    1. In boost mode - with a load of 2.5 ohm / 20W  Bq25895 is unable to deliver a current and output falls to 0v.

    As per the datasheet, the boost fault in REG0C occurs due to the following reasons.

    1. VBUS overloaded in OTG

    2. VBUS OVP (Over Voltage Protection)

    3. The battery is too low in boost mode.

    While testing boost mode the supply on the VBUS pin was not connected so 1st two points are ruled out also we did a test with a fully charged battery which ruled out the 3rd point as well.

    So please help us to resolve this issue.

    Thank You

  • 0 in reply to Piyush Charpe
    TI__Guru 57651 points

    Hi,

    Please measure the BAT pin voltage and see if it goes to low. Referring to 8.2.5 Boost Mode Operation from Battery on the d/s, The boost output is maintained when BAT (BAT pin voltage) is above VOTG_BAT threshold.

    Thanks,

    Ning.