AVPro® 5002R

Dual SCART A/V Switch

DATA SHEET

Page: 21 of 30

Rev 2.1

AUXILIARY Red / Chroma Bi-directional Operation:

For the TV source selection of Auxiliary RGB (Register 1 xxxxx001) and S- video (Register 1 xxxxx101), the output

driver on the Aux_Cout pin acts as part of the load for the RED/Chroma signal input on pin 15 of the SCART connector.

In order to get the correct 75Ω load impedance, the Aux_Cout amplifier needs either a DC bias, an extra resistance to

ground, or a FET pulldown.

1). To select an internal DC bias for the Aux_Cout amplifier, the Aux A/V source should be set for S-video mode

(SVHS Enc 1, Enc 2, Enc 3 or Enc 4) per the following table. This puts 0.9 VDC bias at the input, or about 1.8V at the

Aux_Cout

pin, and 0.9V at the auxiliary SCART connector when terminated (driven) in a 75Ω system. Therefore, the

outputs of the external video encoder must be disabled in this mode in order to prevent corruption of the incoming

RED/Chroma video signal.

2). As an alternative, to select a 0V DC bias for the Aux_Cout amplifier, the Aux A/V source should select one of

the Composite modes (Enc1, ENC2 or TV) or Aux mute in the following table. In this mode, the internal amplifier bias

set to 0V, but amplifier is a weak pulldown. The amplifier is biased between ground and +5V, as such, the output

impedance of the Aux_Cout is around 100Ω including the 75Ω series resistor. A shunt resistor of 330 to 470 Ω will

compensate, but will slightly lower the Aux_Cout chroma signal.

3). Another option is to add a FET with ~20Ω series resistor from the Aux_Cout to ground. Select 0VDC bias for

the Aux_Cout amplifier, and bias the FET in the “ON” or conducting state. The Aux A/V source should select one of the

Composite modes (Enc1, ENC2 or TV) or Aux mute. See the Register 1: Audio/Video Control bit table for settings. This

method will compensate for the Aux_Cout pin pulldown, and not significantly reduce the Aux_Cout chroma signal.

Mux

Aux_R

Aux_Cout

Aux_Cin

75

Ω

Auxiliary

SCART

Pin 15

Mux

Mux

Option 2

R = (330-470

Ω)

or

5002R

Option 3

FET + R = 20

Ω

Note: Aux_Cin is not available on the 48QFN package

HOT-PLUG OF SCART CONNECTORS

Semiconductor ICs can be sensitive to discharges caused by floating chassis grounds between audio/video equipment.

This is observed when the SCART cables are repeatedly connected and disconnected while the ICs are powered on

inside the IRD. When the SCART cable is unplugged, an AC potential can exist between equipment. When the SCART

cable is plugged back into the IRD, the AC potential discharges through the SCART connector. If the discharge occurs

through the shield of the SCART connector or the ground pins, there is no problem. If the discharge occurs through the

signal pins, semiconductor devices can experience potential issues. These issues will occur if the pulse created by the

discharge has a fast rising edge, typically a few hundred pico-seconds. This is an order of magnitude faster than a

standard ESD pulse so the internal ESD diodes of ICs will not respond fast enough to protect the device. This issue can

be resolved by placing a small shunt capacitor on each SCART I/O pin. The capacitor slows the rising edge of the

discharge pulse and allows the internal ESD diodes to react to the discharge. An exact value should be calculated for

each signal line depending upon the signal type so as to avoid roll-off of the intended signal. (see Equivalent Circuit

section)