CN0422 provides a completely isolated connection between a High-Definition Multimedia Interface (HMDI) source and HDMI sink device. Isolation in this circuit increases system safety and robustness by providing protection against electrical line surges and breaks the ground connection between bus and digital pins, thereby removing possible ground loops within the system. ADP7104-3.3 low dropout linear regulator together with ADP5302 high efficiency, ultralow quiescent current step-down regulator provides low noise supply voltage to the system with high power supply rejection. The ADN4654 1.1 Gbps Low Voltage Differential Signaling (LVDS) isolator is used to isolate the CML signals using the coupling and decoupling networks shown in Figure 1. The coupling and decoupling networks allow reliable translation between CML and LVDS voltage levels. The circuit shown in Figure 1 also provides bi-directional isolation of the Consumer Electronics Control (CEC), Hot Plug Detect (HPD) and Display Data Channel (DDC) signals using ADuM1250 I2C isolators. Two ADuM5020 low emission isolated DC-DC converters provide isolated power to the ADN4654 and ADuM1250 devices. The HDMI V1.3a standard requires that a compliant HDMI source provide 275 mW of power to a HDMI sink device. The ADuM5020 provides 275mW to the HDMI sink via the DDC +5V pin located on the HDMI receptacle.
The system can transparently isolate a HDMI interface that is configured for resolutions of up to 1280p × 720p (720p) at 60 Hz and is rated to a withstand voltage of 2500 V per UL 1577.
Figure 1. EVAL-CN0422-EBZ iCoupler® Isolation for HDMI Simplified Circuit Diagram
Figure 2 shows a simplified block diagram of the power isolation and the isolation of the HDMI Version 1.3a signals. Number 1 through Number 5 show the start-up communication sequence through the ADN4654, ADuM1250, and ADuM5020 devices between the HDMI source and HDMI sink.
Figure 2. Isolated HDMI Signal Flow Diagram
To test the EVAL-CN0422-EBZ in your system, first connect a 5V / 1A power supply to the connector J5 on the EVAL-CN0422-EBZ circuit board using a Micro USB Type B cable. This provides power to the isolation circuitry. The HDMI input is located on the underside of the EVAL-CN0422-EBZ circuit. This should be connected to the HDMI source. The HDMI output connector (J4) is located on the top of the EVAL-CN0422-EBZ circuit. This should be connected to the HDMI sink. The device is plug and play, no programming is required to initialize the circuit board.
Figure 3. EVAL-CN0422-EBZ iCoupler® isolation connections.
A system compatibility test can be performed to compare an isolated and non-isolated display. This test setup is described below.
Figure 3. EVAL-CN0422-EBZ iCoupler® isolation for HDMI test setup.
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