• State TI Thinks Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 3 answers
  • Subscribers 64 subscribers
  • Views 306 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25910EVM-854: BQ25910EVM-854 The efficiency test result is about 1% lower than datasheet

Star Xu
Genius 9645 points
Part Number: BQ25910EVM-854
Other Parts Discussed in Thread: BQ25898, BQ25910, BQ25898D

Hi

The customer test with the BQ25910EVM, The efficiency test result is about 1% lower than datasheet. For example, at the peak efficiency (VBUS = 5V, VBAT = 3.8V, charging current 1.1A), the measured efficiency is 94.5%.

The register set as below:

I2C address

Reg address

Write command

description

6A

00

C8

Master HIZ enable

6A

07

8D

Master WD disable

4B

05

DD

25910 WD reset

4B

05

8D

25910 WD disable

4B

06

3B

25910 CHG enable

Test point as below:

Input voltage: GND_ s & VUS2_ S

Input current: R19 (R21 mentioned in datasheet is not welded on the board and bypasses ron_qblk)

Output voltage: Vout_ 910_ S (BAT_S in datasheet is unreasonable, BAT_S is connected with bq25898) & GND_ S

Output current: R20

Ambient temperature: 25 ~ 30 ℃. The SW and fly cap waveforms of bq25910 are normal.

VBUS=5V，VBAT=3.8V。 VBUS and VBAT are adjust slightly according to the change of charging current.

What other factors will affect the efficiency of the test?

Waiting for your reply.

Thanks

Star

  • 0
    TI__Mastermind 33605 points

    Hi Star,

    Were the VBAT and VBUS measured exactly on the corresponding testpoints?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Genius 9645 points

    Hi Mike Emanuel

    Thanks for your reply.

    The test points as below:

    Input voltage: GND_ s & VUS2_ S

    Input current: R19 (R21 mentioned in datasheet is not welded on the board and bypasses ron_qblk)

    Output voltage: Vout_ 910_ S (BAT_s in datasheet is obviously unreasonable, BATt_s is connected with bq25898) & GND_ s

    Output current: R20

    Are these test points selected correctly?

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Guru*** 148315 points

    Hi Star,

    Those are the correct test points.  Is the BQ25898 in HiZ mode?  R19 and R20 have some variability but I do not expect that to adjust efficiency by 1%.   The datasheet has DFE252012F-R47M with DCR=0.017ohm typical but 0.023ohm max.  It is possible that the inductor used for the datasheet curves has lower lower DCR than the one on the EVM.  But that's only 1.1A^2*(0.023-0.017)ohm=7milliwatts of loss.  I have an EVM in the lab and will quickly test using Keithley sourcemeters later today.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru*** 148315 points

    Hi Star,

    I get 95.2% on my EVM using Keithley meters with .

    VBUS=5V, IBUS=0.854A, VBAT=3.8V, IBAT=1.07A.

    If I only disable charge on BQ25898D instead of HiZ (or removing the series sense resistors), I get 94.8% efficiency.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hi Jeff,

    It's me to ask this question.

    the meter I use is KEITHLEY DAQ6510. And I also try using another meter, but get same result. So I think the error is not because of meter.

    I tested inductor resistance  on my EVM--It's 16.67mohm

    BQ25898D SW stop when I test efficiency. (It means BQ25898D enter HiZ mode, right?)

  • 0 in reply to jizhi Qi
    TI__Guru*** 148315 points

    Hi Jizhi,

    Unless the BQ25898D is in HiZ or completely removed from the circuit, it has noticeable leakage at VBUS and BAT pins.  Can you retest on the EVM after removing R2 and R4?  This is will completely remove the BQ25898D.  Also, when measuring VBUS and BAT using TP25 and TP26, please ensure that the grounds are connected to the same ground test point.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hi Jeff,

    after removing R2 and R4,test result is similar, 

    Vin 101 Iin 102 Vbatt 103 Ibatt 104 efficiency
    4.9962 6.983 3.8 8.65 94.21%
    5.004 7.369 3.8 9.154 94.33%
    5.0024 7.768 3.8 9.65 94.37%
    5.0015 8.166 3.8 10.147 94.41%
    5 8.564 3.7999 10.64 94.42%
    4.9992 8.964 3.7999 11.139 94.45%
    4.9978 9.367 3.8 11.633 94.43%
    4.9965 9.775 3.8 12.136 94.42%
    4.995 10.179 3.8 12.632 94.41%
    5.0052 10.56 3.7999 13.13 94.40%

    This is same as expected. Because no matter BQ25898D exist or not ,we tested BQ25910 current and voltage. Efficiency test result should NOT change after remove other parts, right?

    Input voltage: GND_ s & VUS2_ S

    Output voltage: Vout_ 910_ S  & GND_ s

  • 0 in reply to jizhi Qi
    TI__Guru*** 148315 points

    Hi Jizhi,

    Ok. I assume, then, that your EVM has a IC with higher Rdson FETs.  There is a variation as shown below:

    Regards,

    Jeff