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Original question:

BQ24617: request for Altium EVM layout source files

BQ24617: current mismatch problems

Shai Berman
Mastermind 7405 points
Part Number: BQ24617

Hi Team,

I have additional question regarding BQ24617 in parallel.

Following TI’s explanations regarding setting thresholds for ISET1/ISET2 pins, I made the setup and worked fine.

But when I tried to decrease I termination below 100 mA, it went wrong:

  • R16 on EVB was set to 750 ohm

  • Viset2 measured = 23.4mV 
  • Actual I precharge measured 100 mA (1 mV on R18), instead of expected 24 mA

 

I do need TI’s advice regarding the current mismatch?

I made more tests, no with I termination 0.05 A (different R16).

Now it stops at a value well below it ~ 20-30 mA. I measuring shunt voltage on R18. My indication of a stop of charge is the STAT2 state, see below:

I did not have a chance to check pre-charge current behavior again.

Can it be a chance that my current mismatch problems are caused by improper batteries technology usage – too low voltages? Attaching my battery spec.

LTO1650 700mAh 2.4V.pdfHTC1865-1300 (005) hunan htc.pdf

Looking forward for your kind respones, Thanks in advance.

Best regrads,

Shai

  • 0
    TI__Mastermind 24075 points
    Hello Shai,
    As per d.s section 9.3.5, the minimum precharge and termination current is actually clamped roughly around 125mA, dependent on the sense resistor you use (typ. 10mohm). This explains your 100mA current observed. Can you detail the setup for how you observed termination current below this minimum current threshold?
  • 0 in reply to Kedar Manishankar
    Mastermind 7405 points

    Kedar, thanks for an answer.

    Actually, it is very simple – I changed R16 to be 1.5Kohm, then observed when the charger stops charging (STAT2 turns on and STAT1 turns off) by measuring Vshunt on R18.

    The value I reached is around 0.3 mV – which correlates 30 mA. Please explain that.

    Also if I change the Rsense value to be 20 mohm instead of 10 mohm, what will be its influence on the theoretical minimum clamping value of I pre-charge?

    Thanks and regards,

    Shai

  • 0 in reply to Shai Berman
    TI__Mastermind 24075 points
    Hello Shai,
    1.25mV differential voltage across SRP and SRN is the threshold before which the charger goes into non-synchronous mode and terminates charging, which means for 10mOhm resistor your termination current would be 125mA. Changing the sense resistor is a way to decrease your termination threshold, and 20mOhm would decrease threshold to 62.5mA, as this current would correspond to 1.25mV voltage across SRP,SRN. In DCM inductor current will go slightly negative and it is discontinous. As SRP SRN voltage corresponds to this current, it is possible you are seeing the average voltage from the inductor current cycle. Scope capture of SRP SRN at termination will show more information.
    If you change your sense resistor to 20mOhm, keep in mind the CHG_OCP comparator (V(SRP-SRN) < 160%(IBAT_REG) and change your inductor value to a higher one to have less ripple.