rclamp0502b Semtech Corporation, rclamp0502b Datasheet - Page 6

• Manufacturer Part Number: rclamp0502b
• Description: Ultra-low Capacitance Tvs For Esd And Cde Protection
• Manufacturer: Semtech Corporation

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
capacitance 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 capacitance, the more extreme the
modifications will need to be. If the added
capacitance is too high, compensation may not even
be possible. The RClamp0502B 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 RClamp0502B. Figure 2 shows
how to implement the RClamp0502B in an HDMI
application (transmitter and receiver). Figure 3 shows
impedance test results using a Semtech evaluation
board with layout compensation. As shown, the device
meets the HDMI CTS impedance requirements.
PROTECTION PRODUCTS
Applications Information
2005 Semtech Corp.
HDMI Transmitter
HDMI Transmitter
Figure 2 - HDMI Schematic
6
Figure 3 - TDR Measurement using Semtech
X-axis
Y-axis
Evaluation Board
1.640
99.2
HDMI Display
HDMI Display
A
A
A
RClamp0502B
B
B
1.855
104.6
B
(nsec)
(Ohm)
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