IP4778CZ38_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 12 February 2009

16 of 26

NXP Semiconductors

IP4778CZ38

HDMI ESD protection, DDC buffering and hot plug control

The combination of a TMDS switch and the IP4778CZ38 is a cost-effective way to attain

various HDMI ports by using a single input HDMI receiver device. The ENABLE signal

activates the HDMI DDC and Hot Plug lines at the port that is selected by the system

controller.

10.6 Backdrive protection

The HDMI contains various signals which can partly supply current into an HDMI device

that is powered down.

Typically, the DDC lines and the CEC signals can force 5 V into the switched off device.

The IP4778CZ38 ensures that at power-down, the critical signals are blocked to prevent

any damage to the HDMI sink and HDMI source.

Fig 12. Example of multiplexing both DDC and Hot Plug

001aag046

ENABLE

DDC_CLK_IN

DDC_DAT_IN

HOT_PLUG_DET_IN

ENABLE

DDC_CLK_IN

DDC_DAT_IN

HOT_PLUG_DET_IN

ENABLE

DDC_CLK_IN

DDC_DAT_IN

HOT_PLUG_DET_IN

DDC_CLK_IN

DDC_DAT_IN

HOT_PLUG_DET_IN

input 1

input 2

input 3

Fig 13. Backdrive protection

001aag047

HDMI ASIC

HDMI source

supply off

5 V

backdrive current

HDMI sink