BQ40Z50 fuse register cannot be toggled

Ran,
The FET Enable (22) command turns FET control over to the FW. If you set FET_EN low, then you can turn the CHG and DSG FETs on and off with the 1F and 20 commands.
Tom

Dear Tom,
what does it mean when this doesn't happens? is it a hardware problem?

Ran,
Are you asking what it means when you cannot open the CHG and DSG FETs? This is expected, if the the FET_EN flag is red. Set is low and you should be able to control the FETs with the 1F and 20 commands. Also, make sure that the pack is unsealed and in full access mode. Maybe a screen shot of the Registers screen would help me to understand the problem.
Tom

thanks,

attached here is the register map.
you can see:

1. SEC(1:0) that says we are in unsealed + full access
2. FET_EN = 1
3. I toggled the CHG_FET a few times as well as DSG_FET
4. FUSE = 1

still CHG_test and DSG_test are cleard

Ran,

Here are some comments about the screenshot.

• SEC 1 =1 and SEC0 = 0; so the gauge is in Unsealed mode, but not Full Access mode. But,this should not matter for what you are trying to do.
• The FET_EN flag is set, so the 1F and 20 commands will not work.
• The FUSE flag is set, so the FETs will be disabled.
• You entered a FUSE toggle command, so you may have set the FUSE flag. If you did not set it, but are trying to clear it, then here are some options.
  
  • If you did not set the FUSE flag, then it could have been set by a PF fault. I do not see any PF faults shown, so this should not be the case.
  • If the FUSE flag is set, and there are no PF faults, then the 2nd level protector may have set it. Check to see whether the FUSE pin on that device is higher than VSS. if it is, then the 2nd level protector has set the flag. Try reducing the cell voltages to 3V to see if it clears. You may have to issue a reset command to clear it.
• If you set the FET_EN flag low, then you can use the 1F and 20 commands to manually control the FETs, but you have to clear the FUSE flag before they will work.

I do not see any other issues that would prevent the FETs from turning on.

Tom

Dear Tom,

we do not use any Secondary protection in the BQ system, our fuse is in series with the battery pack.
indeed for some reason the FUSE pin (which floats to a test point) has 0.8V on it.
grounding it solved the problem and reset the FUSE pin.

now all actions of calibration and normal operation of FETs is available (!).

what is your recommendation when not using fuse pin?
meaning, fuse pin is now grounded, but should we also disable it and the protection that check its activity?
other suggestions?

regards,
Ran