CM2031 Datasheet, PDF (8/18 Pages) California Micro Devices Corp – HDMI Receiver Port Protection and Interface Device

CM2031
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.)
Rev. 5 | Page 8 of 18 | www.onsemi.com