05-26-2019, 04:30 PM
(This post was last modified: 05-26-2019, 05:03 PM by Nikolay_Po.
Edit Reason: A circuit added
)
As I can see at the page 18 of rockpro64_v21-SCH.pdf, there may persist auto-boot feature, take a look at a diagram, marked red.
![[Image: attachment.php?aid=1334]](https://forum.pine64.org/attachment.php?aid=1334)
If these components are installed, the board will turn on when the power is applied. If it is not turning on, check the network at pin #34 (VDC) of U5 RK808-D chip. When the voltage on this pin is raising above 0.6V the power supply IC will turn on the power.
IMHO, the network on this pin is strange. If the voltage will rise slowly (it shouldn't because the voltage is producing by a 12 to 5V buck converter), the capacitor C204 will charge slowly and may not to produce enough VDC pulse. Also the VDC input of supply system IC has a debouncing time of 100ms. And in some circumstances the pulse may be not long and high enough to be detected with a margin.
I have none board yet and can't check the speed of voltage rise at RK808 #34 VDC pin. And I don't know what reasons have board developers to make such capacitor-coupled startup circuit. Probably it is perfectly OK and just was not installed.
Just for a reference, here is the network from RK808 data sheet:
![[Image: attachment.php?aid=1335]](https://forum.pine64.org/attachment.php?aid=1335)
This circuit should turn the power system on at about 8V input. But sure, it is not so simple as at a glance. The LDO above the buck converter is not present in the design of ROCKPro64 v2.1. The voltage at the VDC will stat rising earlier than 5V buck regulator VCC5V0_SYS output and VCC_RTC voltage. That is the cause the RK808 may not turn on. It will not see the voltage rise and power-on interrupt will not trigger, no power-on will happen. Probably, this was a reason to implement the startup circuit as shown at top diagram.
In case of auto-boot circuit is present but not working, I'd recommend to try this circuit (in red):
![[Image: attachment.php?aid=1336]](https://forum.pine64.org/attachment.php?aid=1336)
If these components are installed, the board will turn on when the power is applied. If it is not turning on, check the network at pin #34 (VDC) of U5 RK808-D chip. When the voltage on this pin is raising above 0.6V the power supply IC will turn on the power.
IMHO, the network on this pin is strange. If the voltage will rise slowly (it shouldn't because the voltage is producing by a 12 to 5V buck converter), the capacitor C204 will charge slowly and may not to produce enough VDC pulse. Also the VDC input of supply system IC has a debouncing time of 100ms. And in some circumstances the pulse may be not long and high enough to be detected with a margin.
I have none board yet and can't check the speed of voltage rise at RK808 #34 VDC pin. And I don't know what reasons have board developers to make such capacitor-coupled startup circuit. Probably it is perfectly OK and just was not installed.
Just for a reference, here is the network from RK808 data sheet:
This circuit should turn the power system on at about 8V input. But sure, it is not so simple as at a glance. The LDO above the buck converter is not present in the design of ROCKPro64 v2.1. The voltage at the VDC will stat rising earlier than 5V buck regulator VCC5V0_SYS output and VCC_RTC voltage. That is the cause the RK808 may not turn on. It will not see the voltage rise and power-on interrupt will not trigger, no power-on will happen. Probably, this was a reason to implement the startup circuit as shown at top diagram.
In case of auto-boot circuit is present but not working, I'd recommend to try this circuit (in red):