According to the TegraK1 embedded design guide, we added the auto-power-on circuit, which use Tegra GPIO_PJ0 to control the AMS3722 AC_OK pin low.There is no problem with this operation.But when I add a battery(3.3V) to the VBAT_BKUP pin of the power management chip AMS3722 (for RTC), the auto power will not work and I still need to press the power button.What’s the reason for this?
No one has this problem？
Hi, there is no auto power on chapter in design guide. Shorting AC_OK pin to ground is not recommended as there could be some potential risk. Please refer to this topic for more info: [url]https://devtalk.nvidia.com/default/topic/795221[/url]
In chapter 2.12 of TegraK1_Embedded_Design_Guide,it is optional Auto-power-on support. Described as follows:
This section provides guidance for modifying a carrier board design to power the platform on when
VDD_MUX (Main supply from AC Jack or equivalent) is first powered, instead of waiting for a power
button press.
The PMIC OTP used on Jetson TK1 has a bit that is set to prevent wake up when power is applied
(auto_off=1). This is what keeps the system from powering up when the main power source is applied,
but instead, waits for a power-on event ( ONKEY, ACOK etc.). Note that there is a requirement for a
minimum delay to allow the RTC out to stabilize, and start-up conditions to reach their properstate. This
required minimum delay is ~220ms.
To support the Auto-Power-On process with the Jetson TK1 PMIC OTP, the following is required:
• Main power source is applied.
• The PMIC detects VBAT rising above ResVoltRise level → waits 200ms for RTC → then because
of “auto_off=1” goes to POWER_OFF state.
• ACOK must be low, so that it will go to VSUP debounce state and set EN5V high. When VSUP
reaches vsup_min level it will begin the start-up sequence.
Circuit Description
The figure above shows the connections necessary to support Auto-Power-On on a Jetson TK1 like
design. The FF sets ACOK low to start the power-on proces when power is applied. After this process is
under way, the main 3.3V supply will be up and this will cause the set FF to drive ACOK high. ACOK
cannot be high during power up, as this will cause the PMIC to go the POWER_off state. Only when
ACOK is low, will the start-up begin. For normal operation ACOK can stay low, but it will prevent the
PMIC from being able to go to the POWER_OFF state (SW command, or an other reason). It will always
start_up automatically as ACOK is low.
When ACOK is high, the POWER_OFF state can be entered as needed. Therefore, the FF drives ACOK
low initially so the system can power-on when the power source is connected, but then drives it high so
that the PMIC can support the POWER_OFF state if desired at a later time.
Just saw that, sorry for mistaking the DG of projects.
Do you mean you have already added the auto-power-on circuit as DG request? The default design is passive cap to vbat_bkup, and the typical vdd RTC is about 2.5v. So a big cap is recommended preferred.