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Errata #4: HAR-3935 – CTRL_FORCE_OFF_MOCI# is pulled-up to wrong voltage
rail
Affected Version: Verdin Development Board V1.0B
Fixed in: Verdin Development Board V1.1A
4.1 Customer Impact
The main power gets killed when the CTRL_PWR_EN_MOCI# goes low and the +V1.8_SW rail is
turned off. This means the main power is killed during a reset cycle, and the power-down
sequence is not graceful.
4.2 Description
According to the Verdin specifications, the CTRL_FORCE_OFF_MOCI# is an open-drain output of
the module, which is 5V tolerant and requires a pull-up resistor on the carrier board. On the
Verdin Development Board V1.0B, the CTRL_FORCE_OFF_MOCI# is pulled up to the +V1.8_SW
rail. Unfortunately, this rail is switched by the CTRL_PWR_EN_MOCI# signal. During a reset cycle
(software or button initiated), the CTRL_PWR_EN_MOCI# signal can go low for power cycling the
peripherals on the carrier board. This is also disabling the +V1.8_SW, which means the
CTRL_FORCE_OFF_MOCI# goes low and triggers the kill input of IC16. The IC16 then kills the
main power of the module. This means resetting the module can cause an unintentional power-off
of the system.
During a regular power-down cycle, the CTRL_FORCE_OFF_MOCI# signal is supposed to go low
as the last step after all the module and carrier board peripheral rails are shut down in the correct
order. Due to the incorrectly pulled up CTRL_FORCE_OFF_MOCI# signal, the main power gets
killed in a too early state. This means the power rails are not shut down in the intended graceful
sequence. Even with this non-graceful shutdown, damages on the module or carrier board are not
expected.
4.3 Workaround
Removing R80 disables the CTRL_FORCE_OFF_MOCI# signal on the Verdin Development Board.
However, this disables the "kill-feature" entirely. Therefore, the supplies are not turned off after a
shutdown, which prevents the system from being turned on by using the power button. For turning
on the system, either power cycle the whole board or turn off the main 3.3V rail on the carrier
board by pressing the power button for >3s. Besides this inconvenience, the modification is
compatible with all Verdin module versions.
An alternate workaround is removing R95 and adding a 100kΩpull-up resistor from
CTRL_FORCE_OFF_MOCI# to +V5_STB. This makes the circuit fully compatible with the new
Verdin modules. The kill-feature would work with this modification as intended with the new
Verdin modules. However, for the older Verdin iMX8M Mini V1.0B module, the
CTRL_FORCE_OFF_MOCI# is not 5V tolerant, and the CTRL_FORCE_OFF_MOCI# signal gets also
asserted during the reset cycle. After the modification, the development board is no longer
compatible with the Verdin iMX8M Mini V1.0B. Read Errata #13 and Errata #5 of the Verdin
iMX8M Mini V1.0B module for more information. The following picture shows one potential
implementation of the alternate workaround patch:
