FN6406 Rev 1.00

Page 10 of 13

Sep 28, 2018

ISL59910, ISL59913

Contrast

By varying the voltage between pins VGAIN and VREF, the gain

of the signal path can be changed in the ratio 4:1. The gain

change varies almost linearly with control voltage. For normal

operation it is anticipated the X2 mode is selected and the

output load is back matched. A unity gain to the output load is

achieved with a gain control voltage of about 0.35V. This allows

the gain to be trimmed up or down by 6dB to compensate for

any gain/loss errors that affect the contrast of the video signal.

Figure 25 shows an example plot of the gain to the load with

gain control voltage.

C

ommon-Mode Sync Decoding

The ISL59910 features common-mode decoding to allow

horizontal and vertical synchronization information, which has

been encoded on the three differential inputs by the EL4543, to

be decoded. The entire RGB video signal can therefore be

transmitted, along with the associated synchronization

information, by using just three twisted pairs.

Decoding is based on the EL4543 encoding scheme, as

described in Figure 26 and Table 1. The scheme is a three-level

system, which has been designed such that the sum of the

common-mode voltages results in a fixed average DC level with

no AC content. This eliminates the effect of EMI radiation into the

common-mode signals along the twisted pairs of the cable

The common-mode voltages are initially extracted by the

ISL59910 from the three input pairs. These are then passed to an

internal logic decoding block to provide Horizontal and Vertical

sync output signals (HOUT and VOUT).

Power Dissipation

The ISL59910 and ISL59913 are designed to operate with ±5V

supply voltages. The supply currents are tested in production

and specified to be less than 39mA per channel. Operating at

±5V power supply, the total power dissipation is:

where:

•PDMAX = Maximum power dissipation

•VS = Supply voltage = 5V

•ISMAX = Maximum quiescent supply current per

channel = 39mA

•VOUTMAX = Maximum output voltage swing of the

application = 2V

•RL = Load resistance = 150Ω

00.8

VGAIN

0.4

1

2

1.8

1.4

1

0.6

0.4

0.6

0.2

1.6

1.2

0.8

FIGURE 25. VARIATION OF GAIN WITH GAIN CONTROL

VOLTAGE

TABLE 1. H AND V SYNC DECODING

RED CM

GREEN CM

BLUE CM

HSYNC

VSYNC

Mid

High

Low

Low

Low

High

Low

Mid

Low

High

Low

High

Mid

High

Low

Mid

Low

High

High

High

NOTE: Level ‘Mid’ is halfway between ‘High’ and ‘Low’

TIME (0.5ms/DIV)

BLUE CM

OUT (CH A)

GREEN CM

OUT (CH B)

RED CM

OUT (CH C)

VSYNC

HSYNC

FIGURE 26. H AND V SYNCS ENCODED

PDMAX

32 VS



ISMAX VS



- VOUTMAX

VOUTMAX

RL

----------------------------



+





=

(EQ. 1)

PDMAX

1.29W

=

(EQ. 2)