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BQ24773 - Max output 0.7V?

sarkis kazarian
Prodigy 220 points
Other Parts Discussed in Thread: BQ24773

I have a pre-production prototype using BQ24773. First time using this part. I modeled after the EVM (SLUUAO3A) and verified layout / parts are the same with one minor exception to replace an obsolete part. At any AC Adapter input, with or without the battery attached, the output of the circuit, as measured at Vsys, output side of the inductor, is 0.7V. I can see the controller appears to be switching the ground MOSFET at the same time as either pass MOSFET - so current is flowing into the ground plane. 

How do I get the proper ~4V output from this device? Data sheet has some inconsistencies, but it states it should be capable of at least 4V.

I have measured waveforms at all nodes, and note the ACOK line is not at ground potential, switching frequency is 800kHz, and other than the phase relationship mentioned above, readings appear correct.

  • 0
    TI__Guru 56650 points
    What is ILIM pin voltage? Could you order an EVM and compare it with your circuit?
  • 0 in reply to Wang5577
    Prodigy 220 points
    I have ordered an EVM module but not received it yet. The voltage @ ILIM pin is 0.026V when opened with any Vin > 1V. I originally set a divider referenced to Vregn with 15k + 186k intended to current limit at 2A, but I have tried open circuit as well as grounding and there is no change in the Voutput.
  • 0 in reply to sarkis kazarian
    TI__Guru 56650 points
    ILIM can't be floating. If it is 26mV, it may be too low to have a normal output.
  • 0 in reply to Wang5577
    Prodigy 220 points
    I have tied ILIM to VREGN (5.4V, or typically 4.8V), left open, and tied to ground. There is no difference in operation under any of these conditions.
  • 0 in reply to Wang5577
    Prodigy 220 points
    Do you have any additional suggestions? The EVM will not arrive until late tomorrow. Thanks.
  • 0 in reply to sarkis kazarian
    TI__Guru 56650 points

    To speed up debugging process, would you tell me which pin voltage or register value do you think it is abnormal?

    Right now, we only know no output. I can list some items.

    For example: a customer didn't connect the IC ground pin to all other ground circuit.

    BTST capacitor is shorted. REGN is shorted.

    VCC doesn't have power. ILIM pin doens't have power.

    CMSRC always ground. ACDET is lower than 2.4V. VCC is higher than 26V...

    Here is sequence:

    1. Check ACDET, ACOK

    2. Check VCC, REGN, ILIM

    3. Check ACDRV, BATDRV

    4. Check BTST, LODRV, HIDRV

    5. Read register value.

  • 0 in reply to Wang5577
    Prodigy 220 points
    I have checked all the nodes, but in reply to your points
    1) IC ground is properly connected to ground circuit [pin 22], center pad is also connected to ground circuit.
    2) BTST is not shorted. REGN is not shorted - it comes up to ~4.8V with 5.0V input as expected. With ~ 5.5V (max due to current limit on the supply) input, REGN settles to 5.4V
    3) VCC has power. It is bypassed to ground and connected via diode to both battery and AC Adapter input.
    4) CMSRC is roughly at ground potential until Vin reaches ~5V (where ACDET hits 2.5V) then is approx 1.3 to 1.4 V.
    5) ACDET is in a 2: 1 divider, 2.5V when Vin is 5.0V.
    6) VCC never exceeds 5.5V

    Sequence:
    In this case, I have my bench power supply current limited to 0.5A. Vsup ~ 5.5V DC input at the AC Adapter input, no battery connected and /BATDET is pulled high to VREGN through 100k ohm resistor.

    a) ACDET = 2.69V
    b) ACOK = ~ 10mV. It is pulled to regulated +3.3V DC, which of course, has no power, but I can see it switch from 0V to 10mV when ACDET crosses 2.5V or so
    c) VCC = 5.50V
    d) VREGN = 5.35V, not stable, approx ±5mV of ripple. Expected, since Vin is low
    e) ILIM = 0.41V
    f) ACDRV = 2.3V DC, has small ripple, 800kHz
    g) BATDRV = 0.32V DC
    h) BTST = 5.06V
    i) LODRV = 0V
    j) HIDRV = 0.65V

    I am working on wiring in an I2C external interface since I do not have on board 3.3V to power the micro. I was hoping a solution would present itself, but will attempt that tonight.

    Sarkis
  • 0 in reply to sarkis kazarian
    Prodigy 220 points

    The EVM just arrived, and I am reviewing document "SLUUAO3B - July 2015 - Revised July 2016". Page 3, paragraph 1.4, notation 1, directs me to a data sheet SLUSC03 to adjust appropriate values, however it is a dead link. Can you provide the proper documentation so I can set this up to match our application?

    Thanks

  • 0 in reply to sarkis kazarian
    TI__Guru 56650 points

    bq24773 full datasheet is not available online. Customer has to send a request to bq2477x_request@list.ti.com.

    And then, the support team know your email and can send the full datasheet to you.

  • 0 in reply to Wang5577
    Prodigy 220 points
    On the EVM the ACDRV/CMSRC are ~ 5V / 12V when operating.
    On my circuit, even after replacing the ACFET and BQ24773, these voltages do not exceed 1.3V. This seems to be a drive issue from the BQ24773. The documentation is not clear - what can suppress the ACDRV and CMSRC signals?
    Thanks
  • 0 in reply to sarkis kazarian
    TI__Guru 56650 points
    What is the resister value between ACDRV and CMSRC? ACDRV only has 60uA driving capability.
  • 0 in reply to Wang5577
    Prodigy 220 points
    4k ohms, same as the EVM. Measuring across both resistors shows (RMS) 29uA current through the CMSRC resistor. ACDRV is far less at 0.25pA RMS.
  • 0 in reply to sarkis kazarian
    Prodigy 220 points

    Solved. Problem with ACFET fixed.

    Question - how do I poll the BQ24773 to receive key parameters - input voltage, output voltage, status? All of the registers are performing programming operations according to the data sheet. Where are the status registers?

    Thanks

  • 0 in reply to sarkis kazarian
    TI__Guru 56650 points
    Great, problem was solved. Do you have the full datasheet? The datasheet has all register description.
  • 0 in reply to Wang5577
    Prodigy 220 points

    I have a data sheet - shall I post it here?

    There are no status registers, only program registers. I need this additional information please. It is not contained in the data sheet.