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Hardware Design

Core Board Design​

Capacitor pads are reserved on the back side of the X3128 core board. Since RK3128 is an entry-level chip, many low-cost designs use 100M Ethernet. Therefore, these capacitors are not populated by default. For projects requiring Gigabit Ethernet, it is recommended to populate the back-side capacitors to reduce packet loss. Baseboard mechanical openings should refer to the development board design and avoid interference with the back-side capacitors.

For differentiation, the core board without these capacitors is X3128CV4, while the populated version is X3128CV4P.

Power Design​

The X3128CV4 core board uses 5V power input. Supplying 5V DC to pins 115, 116, and 117 powers the core board.

Key power pins:

  • Pins 115, 116, and 117: core-board power input, 4.8V to 5.5V / 1A by default.
  • Pin 119: RTC power input, 3V / 50mA.
  • Pins 120 and 121: battery interface.
  • Pins 72, 73, 109, and 110: common ground.
  • Pins 1 and 144: PMU common power output, usually 3.5V to 5V depending on input voltage, available for system power.
  • Pins 123, 124, 125, and 126: PMU LDO1, LDO2, LDO6, and LDO5 outputs, adjustable voltage.
  • Pins 36 and 37: 3.3V output for baseboard power.

USB Design​

RK3128 provides one HOST port and one OTG port. The OTG port can work as either HOST or DEVICE.

For PCB routing, pins 23 and 24, HOST_DP / HOST_DM, form one USB differential pair. Pins 25 and 26, OTG_DP / OTG_DM, form another USB differential pair. Length matching and impedance control are recommended. The target differential impedance is about 90 ohms; otherwise, USB transmission may become unstable.

HDMI Design​

RK3128 integrates an HDMI controller and supports HDMI 2.0. Pins 12 to 19 of the core board are four HDMI differential pairs. These traces require length matching and approximately 100-ohm differential impedance control. Otherwise, HDMI color loss or intermittent display may occur.

LCD Interface Design​

RK3128 integrates RGB, LVDS, and MIPI LCD controllers. To reduce cost, these three groups of LCD pins are fully multiplexed. Only one of RGB / LVDS / MIPI can be used at a time. When configured as LVDS or MIPI, the interface is suitable for higher-resolution LCD panels. Differential pair length matching and impedance control are required, with a recommended impedance of about 100 ohms.