Problems found when using the FS6500 watchdog reset

[普润许]

   We found a problem during the test. When some products of the FS6500 watchdog timed out and generated a reset, they would directly enter LPOFF-deep FS instead of a normal reset. About one of the 10 products will have this problem.
   I checked the levels and found that the RSTB pin went low and there was a zigzag fluctuation on the VCCA at reset.
   Later we tried a lot of solutions and finally found that this problem can be solved by changing the pull-up resistor of FS0B.

This problem does not occur again when I change this resistor from 10k to 1K.

But we still haven't figured out the cause of the fault. We didn't use FS0B. This resistor will be removed and the fault will not be solved.

I hope that you can give some help.

[guoweisun]

Hi

Please see below comment:

1:If you don't use FS0B you should also connect it to VDDIO by pull up resistor 10K.

2:---

The fault error counter is incremented by 1, each time RSTB and/or FS0B pin is asserted.

When FS0B is asserted, the fault error counter is incremented by 1, every time the watchdog error counter maximum value is reached.

The fault error counter has two output values (intermediate and final).

•The intermediate value can be used to force the FS0B activation or to generate a RSTB pulse depending on the FLT_ERR_IMP_1:0 bit configuration in INIT_FAULT register.

•The final value is used to handle the transition to deep fail-safe when the SELECT pin is connected to Ground. If the SELECT pin is connected to VPRE, the main state machine remains in normal mode and the regulators remain on.

---

Please check your select pin connection.

[普润许]

Hi

My VDDIO selects 3.3V VCCA. FS0B has been pulled up to VCCA by 10K.
I have not used FS0B, but I have tested it to feed the dog and release FS0B normally. If I release FS0B first and then trigger the watchdog, there will still be this problem, RSTB will be continuously pulled low. The FS6500 is powered off after a while.
If the faulty board is pulled up by 10k and replaced by 1k, this fault will be solved.

[guoweisun]

For your FS0B according your configuration,you can pull up to 5K to VDDIO/VCCA.

--

• If the pull-up is connected to VDDIO, the value recommended is 5.0 kΩ, there is no current in LPOFF since VDDIO is off in LPOFF model.
• If the pull-up is connected to VSUP3, the value must be above 10 kΩ, there is a current in the   pull-up resistor to consider at application level in LPOFF mode.