CM2030 Datasheet, PDF (6/17 Pages) California Micro Devices Corp – HDMI Transmitter Port Protection and Interface Device

CM2030
When I²C devices are driving the external cable, an internal pulldown on DDC_XX_IN guarantees that the VOL
seen by the ASIC on DDC_XX_IN is equal to or lower than DDC_XX_OUT.
Multiport DDC Multiplexing
By switching LV_SUPPLY, the DDC/HPD blocks can be independently disabled by engaging their inherent
“backdrive” protection. This allows N:1 multiplexing of the low-speed HDMI signals without any additional FET
switches.
Consumer Electronics Control (CEC)
The Consumer Electronics Control (CEC) line is a high level command and control protocol, based on a single
wire multidrop open drain communication bus running at approximately 1kHz (See Figure 3). While the HDMI
link provides only a single point-to-point connection, up to ten (10) CEC devices may reside on the bus, and
they may be daisy chained out through other physical connectors including other HDMI ports or other dedicated
CEC links. The high level protocol of CEC can be implemented in a simple microcontroller or other interface with
any I/OD (input/open-drain) GPIO.
CEC
RX
I/OD
GPIO
TX
Figure 3. Typical µC I/OD Driver
To limit possible EMI and ringing in this potentially complex connection topology, the rise- and fall-time of this
line are limited by the specification. However, meeting the slew-rate limiting requirements with additional
discrete circuitry in this bi-directional block is not trivial without an additional RX/TX control line to limit the output
slew-rate without affecting the input sensing (See Figure 4).
CEC
RX
TX
TX_EN
Slew Rate
Limited
3-State Buffer
X
Figure 4. Three-Pin External Buffer Control
Simple CMOS buffers cannot be used in this application since the load can vary so much (total pullup of 27kΩ to
less than 2kΩ, and up to 7.3nF total capacitance.) The CM2030 targets an output drive slew-rate of less than
100mV/ms regardless of static load for the CEC line. Additionally, the same internal circuitry will perform active
termination, thus reducing ringing and overshoot in entertainment systems connected to legacy or poorly
designed CEC nodes.
Rev. 5 | Page 6 of 17 | www.onsemi.com