• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Subscribers 63 subscribers
  • Views 758 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

UC3906 batt full LED light up prematurely

John Thomas71964
Prodigy 80 points
Other Parts Discussed in Thread: UC3906

If  the batt voltage is 11.7V connected to the circuit, and I power on the PCB, the batt full LED light up. Why?

If i were to use a 11V battery, only power LED light up which is correct.

  • 0
    TI__Guru**** 150870 points

    Please post a schematic of your circuit.  The UC3906 does not have a batt full light, so I am not sure what you refer to.

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    What is yr email address so i can send the schematic for you to chk?

  • 0 in reply to John Thomas71964
    TI__Guru**** 150870 points

    In your schematic, you use the STAT1 pin to indicate full charge or not.  STAT1 will go high impedance when the battery is in float mode, which would indicate a full battery.

    When the IC is unpowered, its outputs are high impedance.  So, when you insert a battery, the voltage on pin 13 goes above the 2.3V reference and you enter float mode.  So, the IC powers up in float mode and then asserts power good and STAT1 and measures voltages.  With your higher battery voltage, when STAT1 is asserted, the voltage at pin 13 is still above the recharge threshold of 90% of 2.3V.  So, you are still in float mode.  You can confirm this by seeing that STAT1 stays low with your higher voltage battery.

    With the lower voltage battery, the voltage at pin 13 goes below the recharge threshold and you start a new charge cycle.

    So, the difference is that your higher voltage battery is in fact full.  It is above the 90% recharge threshold of the IC.

    Possibly if you power the IC first and then insert the battery, it will not jump to float mode first but begin in boost mode and go through a full charge cycle.

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    Thanks Chris for the information. How do i adjust the resistor so that it will trigger full charge cycle if batt voltage <11.8V? The batt is always connected to charger so there is no way for me to power on the charger first and then connect the batt.

  • 0 in reply to John Thomas71964
    TI__Guru**** 150870 points

    You need to either not go above 2.3V initially or go back below 90% of 2.3V after power is connected.

    To do the first, you could tie R16 to ground instead of power good.  This would increase your standby leakage.

    To do the second, some circuit that pulls current out of the pin 13 net to reduce the voltage there is needed.  Perhaps Vin can drive a transistor that is connected to pin 13 through a capacitor.  When Vin is applied, the transistor turns on and pin 13 is briefly shorted to ground through the cap--some current is pulled off pin 13 to charge the cap.  You could try connecting C8 to ground through a transistor to see if this works.

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    I connect R16 to gnd. with the batt (fully charged) remain connected, sometime when i power cycle the charger PCB, the ochg change to LOW forever even after 1 day. The current to batt is 90mA-110mA. If I power cycle again, it shows batt full (correct), charger currect drop below 50mA.

    Why?

     

  • 0 in reply to John Thomas71964
    Prodigy 80 points

    Batt charging voltage remains at 14.12V forever, it never increase further when ochg_ind =LOW.

  • 0 in reply to John Thomas71964
    TI__Guru**** 150870 points

    You need to measure the charging current and voltage and look at the STAT1 and STAT2 output pins to see what state the IC is in.  This tells you what it is trying to do.

    14.12V may be the boost charge level.  There are tolerances in the resistances and in the reference that might shift this voltage a little bit from what you set it to (around 14.5V?).  As long as the pack voltage is that voltage and the charging current is decreasing, then the battery is being charged.  The IC should eventually transition to float charge.