nRESET timing in TPS65217A

The deglitch time for nRESET is spec'd at 30ms.  So, any amount of time greater than 30ms will cause reset.

The 1s just means that the IC will go to default after 1 second.  However, the nRESET signal does not need to be low during that entire time.

thanks a lot Stephen,

a customer is using the part and he is having problems with the nRESET: sometime it works fine, other times doesn't (and got latched, so that a POR is needed)...

attached some waveforms of the main signal:

• Channel 1 (yellow) is net VPMIC of the schematic, connected to pin AC of PMIC. This net is 5V output of LM20343.
• Channel 2 (blue) is net PMIC_RST that is connected to pin nRESET of PMIC. This net is the output PGOOD of LM20343.
• Channel 3 (purple) is net 5V0, that is connected to pin SYS of PMIC (it´s the output controlled by power path of the PMIC of the AC input). It´s similar if customer measure DC/DC outputs of the PMIC.
• Channel 4 (green) is net 24, used in the input of LM20343 and EN of LM20343 using resistance divisor by R2 and R3. Actually R2 is 130K and R3 10K. These values are used to disable supply when input voltage falls below 17V approx. and it start activated again when input voltage reach 17.5V approx. Customer change input value (There are 1300uF on the input) and he get easily top ut LM20343 working properly and PMIC disabled.
• In the first image (tek00008.png) you can see 3 fast cycles, the first 2 are OK and the third is wrong. In the second image (tek00009.png) you see 2 cycles, first is OK and second one is wrong.

any help?

Testing the device, I have seen that releasing the nRESET before 1sec after pulling it down doesn't reset the device, but it actually suddenly jumps to the Active state.

While the device is in its ACTIVE state I push down the nRESET pin, and I can see that the device enters in RESET state.

The problem is that when I release the nRESET pin and push it up, 100ms after having pushed it down, the device immediately goes to the ACTIVE state, without waiting 900ms more, so the 1 second in RESET state it’s just not happening.

could you help me understanding if this is a wrong description in datasheet or we are missin something here?

many thanks in advance

Vincenzo

hello,

Customer is still having the same problem...

<< I have disconnected the nRESET input as it still has a pull-up inside the IC (as stated in datasheet), so now I am not switching the nRESET pin, I am just switching the AC pin (which is normal, every normative specifies to do some power cycling tests on the input of your system) and I am having the same problem (the system doesn’t recover by itself, and you have to manually cycle the power to get the system working again, which is not acceptable). >>

Also, I am still seeing that when the circuit goes to RESET state it doesn’t stand there for 1 second as is specified in the datasheet, so, as I understand, it doesn’t fulfill with the datasheet’s specifications.

could you please help me in clarifying the behavior of the device?

many thanks in advance

Vincenzo