AM3352: High pulse on PMIC_POWER_EN during shutdown

Jesse Caparangca

Part Number: AM3352
Other Parts Discussed in Thread: TPS65217

Hello,

We have a custom board based on the Beaglebone Black (AM335x + TPS65217). We're noticing a 10ms pulse on the PMIC_POWER_EN line around 2ms after SYS voltage starts to drop during a shutdown routine (ALARM2 shutdown). We're wondering if this is normal behavior?

Lightblue - SYS; Darkblue - PMIC_POWER_EN; Pink - PGOOD (PORZn of SoC)

At the moment, we're getting an intermittent unintentional reboot 1sec after SYS voltage drops. But we see this pulse regardless of a reboot or not.

We believe that the pulse happens just as LDO_PGOOD (RTC_PORZn on the SoC) goes LOW therefore putting the RTC section of the AM3352 into RESET state where PMIC_POWER_EN is default HIGH. Then since the SYS supply is already dropping, it loses its pull and goes down with it. Is there anyway we can prevent this from happening?

We have LDO_PGOOD, PGOOD, and PMIC_POWER_EN configured just like the Beaglebone Black. (We're unable to probe LDO_PGOOD at the moment since there aren't any accessible probing points for it).

Thanks,

Jesse

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

Hi,

What Linux version is this? Why is the SYS supply going down?

0 Jesse Caparangca over 8 years ago in reply to Biser Gatchev-XID

Intellectual 590 points

Hi Biser,

It's 3.14.43.

About SYS going down, some guys on the PMIC forum have confirmed that SYS goes down immediately when using the PWR_EN and OFF bit shutdown method. Power path gets cut and SYS is connected to the BAT pins and is only held up by whatever capacitance it has. In our case, BAT is floating. But, by shutting down the system by writing to the PMIC SEQDWN bit register SYS will stay up.

Regards,
Jesse

0 Yordan Kovachev over 8 years ago in reply to Jesse Caparangca

TI__Guru**** 161600 points

Hi Jesse,

Sorry for the delay. I'll look at this and provide my feedback tomorrow.

Best Regards,
Yordan

0 Yordan Kovachev over 8 years ago in reply to Yordan Kovachev

TI__Guru**** 161600 points

Hi,

I think the PMIC_PWR_EN pulse during power down is normal. See the following chunk of code from drivers/mfd/tps65217.c:
/* Set the PMIC to shutdown on PWR_EN toggle */
if (status_off) {
ret = tps65217_set_bits(tps, TPS65217_REG_STATUS,
TPS65217_STATUS_OFF, TPS65217_STATUS_OFF,
TPS65217_PROTECT_NONE);
if (ret)
dev_warn(tps->dev, "unable to set the status OFF\n");
}

Best Regards,
Yordan

0 Jesse Caparangca over 8 years ago in reply to Yordan Kovachev

Intellectual 590 points

Hi Yordan,

Thanks for the response.

I'm not sure if I understand what you are saying. Are you saying that the short HIGH pulse on PMIC_PWR_EN is normal because the code you referred to is setting the PMIC status register OFF bit to 1?

If so, I think the OFF bit of the status register has no effect on PMIC_PWR _EN. Setting OFF bit to 1 will trigger the PMIC shutdown sequence and put it into OFF state when PMIC_PWR_EN is pulled LOW. Setting OFF bit to 0 will place it in SLEEP state when PMIC_PWR_EN is pulled LOW, instead.

PMIC_PWR_EN is controlled by the AM335x's RTC and, during shutdown, is set to go LOW when ALARM2 is met. PMIC_PWR_EN is an active low signal.

Regards,

Jesse

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AM3352: High pulse on PMIC_POWER_EN during shutdown