Forlinx SBC OKMX8MPQ-C, User Manual

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Appendix 1 Carrier Board Designing Tips
1. IIC
IIC can be mounted with multiple slave devices, please make sure addresses are not conflict;
IIC should be added with pull-up resistor, but please do not use multiple resistor pulled-up;
Please notice that SoM IIC voltage and slave device IIC voltage should be matched.
2. WDOG_B
On SoM, WDOG is circuited to power chip by GPIO of CPU, when CPU internal watchdog works, it will
pull-down this signal to trigger power chip reset. It’s suggested to be suspended on carrier board.
3. USB
USB_VBUS_3V3 is detection signal, its voltage should not exceed 3.6V, it can not directly circuited to
VBUS_5V from USB connector.
To make MicroUSB to USB2.0 OTG, please take GPIO as ID pin for identity recognition;
To satisfy USB eye pattern demand, USB3.0 TX/RX PCB length should be less than 6 inches.
4. AD28_SD2_RESET_B
LD44 pin AD28_SD2_RESET_B is internal circuited to VSD_3V3 on SoM, used for reset carrier board SD card,
please suspend it on carrier board.
5. R26_NAND_DQS
RU75 pin R26_NAND_DQS should be suspended.
6.Signals not used by SoM could be suspended, but please circuit all of them to GND.
7.power sequence
We kindly suggest users taking Forlinx carrier board designing for reference, take VDD_3V3 output from SoM to
enable carrier board power, strictly control power sequence, otherwise, it may cause below problems
Power on current over large;
Device booting failure;
CPU failure
7. about IO power leakage
Before the SoM is powered on, if there are SoM pins with high level sink current, it will supply power to SoM,
the red indicator on SoM will shine, and it will detect VDD_3V3 power, which may cause incorrect power
sequence, thus to cause serial power leakage. So the debug port on carrier board is designed with anti-leakage
circuit. Users can take Forlinx designing for reference.