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BQ24773: Bring up of new board integrated with BQ4050

Donovan Sydow
Intellectual 300 points
Part Number: BQ24773
Other Parts Discussed in Thread: BQ4050, BQSTUDIO, BQ24770, EV2400

Hello,

I've spent some time with bring up of new board that integrates the EVM designs from the BQ4050 and the BQ24773, so I have a couple of questions with proper power on option for both of these chips. 

First off we have an error in the layout where the FUSE pin on the bq4050 is tied to ground. Considering this is a short, would this prevent the bq4050 from turning on? VCC/PCHG/PTC/PTCEN/BAT are all at 16v, CHG is 8v, PACK remains 0v, unless shorted, but drains low. 

Secondly, the BQ24773, which is my main question doesn't seem to drive BAT or BATDRV high at all. We are using this with a 4S configuration. When VCC is powered at 19.6v, I get ACDET at 2.6v, CELL/REGN/BTST at 5.4v, which seems good. I have BATPRES tied to GND (120KOhm) at the moment to force the chip to output power, but I can't seem to get BAT or BATDRV to turn on the FETs. The most voltage I get from BAT is .01v. On the EVM in this configuration I measure BAT at 8v and BATDRV at 16v. 

Curious if you have any suggestions, tips, or other things to try and bring either of these chips up. 

  • 0
    TI__Guru**** 165786 points
    Donovan,

    Regarding the bq24773, if the BAT pin is measuring 0.01V then you do not have a battery pack or battery simulator attached, correct? You are trying to use the charger as a dc/dc converter only and not charge a battery? What is the voltage at SRP? Have you set the IC's charge current and charge voltage registers above their defaults, via SMBUS?
  • 0 in reply to Jeff F
    Intellectual 300 points
    Thanks for your Reply Jeff F,

    With regards to BAT pin, I have tried with and without a battery. Although the BQ4050 doesn't enable PACK+, so it doesn't energize the BAT line, which in turn would normally trigger a TPS3898ADRYR, and pulldown the BATPRES. For now I have BATPRES held low with a weak pulldown to ground in hopes it would turn on the BQ24773, SRP/SRN is .05. Unfortunately, I am unable to communicate with the BQ24773 with a EV2400 and bqstudio reports an ACK error (plugged into i2c port rather than SMBUS as this should be the i2c part, bq24770 is the SMBUS part), so I feel it is not turning on, even though the internal LDO is energized and the REGN line is at 5.4v.
    At this point looking to use it as a DC/DC converter, similar to the EVM with a SYS/BAT output. I have also desoldered other parts, and rerouted lines and at this point from a schematic perspective it is identical to the published EVM schematic so I can't understand why it isn't turning on.

    Appreciate any help or thoughts you can provide.
  • 0 in reply to Donovan Sydow
    TI__Guru**** 165786 points
    If BTST is only at 5.4V=REGN, then you are not switching. Are the two ACFETS, driven by ACDRV, on? Is there voltage at ACN pin?
  • 0 in reply to Jeff F
    Intellectual 300 points
    ACDRV and CMSRC are both 0, pretty much everything else is as well that I haven't called out. So the FETs are not turned on. I found a problem with the schematic where ACDRV was tied to the BAT line via a .047uf cap, and suspect that may have damaged the gate of the FET by potentially overvolting it. I've popped that cap, but haven't seen any progress. Tyrns of the SMB.i2c problem is related to the voltage, as I didn't have a 3.3v rail hooked up.
  • 0 in reply to Donovan Sydow
    TI__Guru**** 165786 points
    Try bypassing the ACFETs and connecting a the 19.xV directly to ACP and see if the BTST increases above your input voltage and SRP comes up.
  • 0 in reply to Jeff F
    Intellectual 300 points
    Well that certainly allows things to power up, and I'm able to get my regulators powered off of VSYS. BTST and SRP come up and at the input voltage I apply although not above it as you suggest.
  • 0 in reply to Donovan Sydow
    Intellectual 300 points
    I'm wondering what the risk of this action was. As of now, if I bybass the FET, the rest of the board powers up, but now the bq24773 no longer powers up its LDO regulator, even if I switch back to providing 19v to VCC. So I went from REGN reading 5.4v to now not working. It seems like the chip itself is now damaged.
  • 0 in reply to Donovan Sydow
    TI__Guru**** 165786 points
    If REGN doesn't come up even with VCC > ACDET threshold then, yes the IC is damaged.
  • 0 in reply to Jeff F
    Intellectual 300 points

    Okay thank you. Should that be normal for this chip to damage itself if the ACFET is bypassed? Luckily I have another board here that I am able to get I2C communication from through the EV2400. I was able to remove the cap that tied the ACDRV to ACP/ACN lines, but this one never seemed to ever have REGN come up, although I can talk to it, which is odd. ACDET is 2.6v and VCC shows 19.4. PROCHOT remains high, while ACOK remains low. Which tells me there is some sort of short. Any other thoughts?

  • 0 in reply to Donovan Sydow
    TI__Guru**** 165786 points
    No. If you apply the same voltage before the ACFET (presumably to VCC) and then after the ACFET at ACP, I wouldn't expect the IC to be damaged. Can you send your schematic?
  • 0 in reply to Jeff F
    Intellectual 300 points
    Sent in a PM. Any idea why the other chip I can communicate via I2C, but can't get REGN voltage.
  • 0 in reply to Jeff F
    Intellectual 300 points
    Thanks Jeff, Let me know how the schematic review goes. I think both of these board may have a damaged chip as I cannot get them to turn on their LDO and REGN lines anymore. I can talk to them though with the EV2400. Not certain how to turn them "on" at this point, even though they have power. I am getting a couple of new ones out of fab, and expect to have a few more tomorrow.
    On the subject of the bq4050, it looks like I can bypass the FUSE_EN and SYSPRES logic by setting them and the NR bit on with the EV2400, which is great. What I can quite test or tell is how can I have the bq4050 energize the PACK+ line automatically. I was able to get it to turn on by using the FET_EN toggle. So then I had it set on in the firmware, but that doesn't seem to enable it to turn automatically once a battery is connected. Is there a combination of settings I should enable or disable to allow the bq4050 to turn on once a battery is connected and it is powered up via VCC?
  • 0 in reply to Donovan Sydow
    TI__Guru**** 165786 points
    Donovan,

    Did this get resolved? I can forward to one of my gauge colleagues if not.
  • 0 in reply to Jeff F
    Intellectual 300 points
    Removing the CAP that tied the ACDRV to BAT line, really was the solution. Anything else we had powered with this was damaged in different ways. Confirmed with a couple of new boards, and working well at this point.