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CM2031-A0TR Datasheet(PDF) 8 Page - ON Semiconductor |
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CM2031-A0TR Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 18 page CM2031 Rev. 5 | Page 8 of 18 | www.onsemi.com Hotplug Output Pullup Logic The CM2031 includes flexible circuitry for active or passive control of the HDMI Sink’s Hotplug Present Output line by integrating the 1kΩ pullup resistor. Section 8.5 of the HDMI Specification allows the HDMI Sink to pulse the HotPlug line “low” for at least 100msec to indicate to the Source that the EEPROM should be re-read. This function can be implemented with a few discrete components as shown in Figure 7. Figure 7. Typical Discrete HPD Switching Circuit The Hot Plug Detect circuit of the CM2031 is specifically designed to provide this “pulse” capability and still pass CTS testing requirements. When a logic “high” is applied to the HOTPLUG_DET_IN pin, an internal switch enables the 1kΩ pull-up. When a logic “low” is sensed on this pin, the 1kΩ logic resistor is disconnected, and a weak pulldown ensures a valid low output on the HDMI cable. 5V Passive Pullup In the most basic implementation, where HOTPLUG is to be asserted only when the HDMI +5V supply is applied, simply tie HOTPLUG_DET_IN to the +5V supply and connect HOTPLUG_DET_OUT to HDMI Connector (Pin 19). Local Power Supply Pullup Passive For a system that needs to inhibit the HOTPLUG signal when the local ASIC low voltage supply (“LV_SUPPLY” on CM2031) has been powered, the designer can simply connect HOTPLUG_DET_OUT to the HDMI Connector (Pin 19) and tie HOTPLUG_DET_IN to the “LV_SUPPLY” which can be 1.5V, 1.8V, 2.5V, etc. Then the internal 1kΩ pullup will be enabled between HOTPLUG_DET_OUT and 5V_SUPPLY. If a weak pullup is used on HOTPLUG_DET _IN, then this still allows dynamic switching by the local ASIC while still retaining the isolation/backdrive protection on this pin. Active Local Pullup Control For a system where a low voltage GPIO signal needs to control the HOTPLUG pin (i.e. if the local system needs to boot up before asserting HOTPLUG) the ASIC GPIO can be connected directly to the HOTPLUG_DET_IN pin to control the 5V pullup “on” and “off.” A logic “low” on HOTPLUG_DET_IN will disable the 5V pullup, and a logic “high” will enable the pullup. (NOTE: If the ASIC Power-ON Reset {POR} default of the GPIO is high-impedance or defaults to an input, then the designer should include a weak pulldown on the GPIO to eliminate any POR glitches.) |
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