CM2031 Datasheet, PDF (7/14 Pages) California Micro Devices Corp – HDMI Receiver Port Protection and Interface Device

Issue X-1
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.
+5V_HDMI (Pin 18)
ASIC
GPIO
1kΩ
HOTPLUG (Pin 19)
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.)
ASIC
GPIO
5V_SUPPLY
1kΩ
CM2031
HOTPLUG_OUT
Figure 8. Simplified CM2031 HPD Circuit
© 2007 California Micro Devices Corp. All rights reserved.
07/10/07
490 N. McCarthy Blvd., Milpitas, CA 95035-5112 ●Tel: [phone] ●Fax: [phone] ●www.cmd.com 7