MAX9598 Maxim Integrated Products, MAX9598 Datasheet - Page 24

• Manufacturer Part Number: MAX9598
• Description: Low-Power Audio/Video Switch
• Manufacturer: Maxim Integrated Products

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Some set-top boxes have a floating chassis problem in
which the chassis is not connected to earth ground. As a
result, the chassis can charge up to 500V. When a
SCART cable is connected to the SCART connector, the
charged chassis can discharge through a signal pin.
The equivalent circuit is a 2200pF capacitor charged to
311V connected through less than 0.1Ω to a signal pin.
The MAX9598 is soldered on the PCB when it experi-
ences such a discharge. Therefore, the current spike
Low-Power Audio/Video Switch for
Dual SCART Connectors
24
Figure 15. VCR_R/C_IN Receives a Chroma Signal from the VCR SCART Connector. Notice that the Pulldown Switch on
VCR_R/C_OUT Is Closed and that the Gain-of-2 Amplifier is Off. The Chroma Signal from VCR SCART IS Looped Through to the TV
SCART in the Above Configuration.
Figure 16. Application Circuit to Connect CVBS and Mono Audio from TV SCART to RF Modulator
______________________________________________________________________________________
0.1μF
VCR_R/C_IN
ENC_R/C_IN
ENC_C_IN
Floating-Chassis Discharge
BIAS
BIAS
BIAS
MAX9598
Protection and ESD
MAX9598
TV_Y/CVBS_OUT
TV_OUTR
TV_OUTL
LPF
LPF
10kΩ
10kΩ
75Ω OR GREATER
75Ω OR GREATER
MONO AUDIO
75Ω
flows through both external and internal ESD protection
devices and is absorbed by the supply bypass capaci-
tors, which have high capacitance and low ESR.
To better protect the MAX9598 against excess voltages
during the cable discharge condition or ESD events, add
series resistors to all inputs and outputs to the SCART
connector if series resistors are not already present in
the application circuit. Also add external ESD protection
diodes (for example, BAV99) on all inputs and outputs to
the SCART connector.
A
A
V
V
OFF
= 2V/V
= 2V/V
MODULATOR
SCART
TV
TV_R/C_OUT
VCR_R/C_OUT
RF
75Ω
75Ω
SCART
SCART
VCR
TV