7

 2006 Semtech Corp.

www.semtech.com

PRELIMINARY

PROTECTION PRODUCTS

RClamp0544M

Applications Information (continued)

The HDMI Compliance Test Specification (CTS) requires

sink (receiver) ports maintain a differential impedance

of 100 Ohms +/- 15%. The measurement is taken

using a Time Domain Reflectometry (TDR) method that

utilizes a pulse with a risetime <= 200ps.

ESD protection devices have an inherent junction

capacitance. Even a small amount of added capaci-

tance on an HDMI port will cause the impedance of

the differential pair to drop. As such, some form of

compensation to the layout will be required to bring

the differential pairs back within the required 100

Ohm +/- 15% range. The higher the added capaci-

tance, the more extreme the modifications will need to

be. If the added capacitance is too high, compensa-

tion may not even be possible. The RClamp0544M

presents <1pF capacitance between the pairs while

being rated to handle >8kV ESD contact discharges

(>15kV air discharge) as outlined in IEC 61000-4-2.

As such, it is possible to make minor adjustments to

the board layout parameters to compensate for the

added capacitance of the RClamp0544M. Figure 7

shows how to implement the RClamp0544M in an

HDMI application (transmitter and receiver). Figure 8

shows impedance test results using a Semtech evalua-

tion board with layout compensation. As shown, the

device meets the HDMI CTS impedance requirements.

Figure 7 - HDMI High Speed Signal Protection Application Diagram

1

1

1

1

Figure 8 - TDR Measurement using Semtech

Evaluation Board

A

B

C

X-axis

1.640

1.796

1.953

(nsec)

Y-axis

99.3

105.3

98.7

(Ohm)

A

C

B