11

LT1395/LT1396/LT1397

139567fc

will remain enabled at all times, then the EN pin should be

mately 30

µA when activated. If using CMOS open-drain

logic, an external 1k pull-up resistor is recommended to

ensure that the LT1395CS6 remains disabled in spite of

any CMOS drain leakage currents.

The enable/disable times are very fast when driven from

standard 5V CMOS logic. The LT1395CS6 enables in

about 30ns (50% point to 50% point) while operating on

±5V supplies (Figure 2). Likewise, the disable time is

approximately 40ns (50% point to 50% point) (Figure 3).

1395/6/7 F02

OUTPUT

EN

1395/6/7 F03

OUTPUT

EN

S

APPLICATI

I FOR ATIO

Differential Input Signal Swing

To avoid any breakdown condition on the input transis-

tors, the differential input swing must be limited to

±5V. In

normal operation, the differential voltage between the

input pins is small, so the

±5V limit is not an issue.

Buffered RGB to Color-Difference Matrix

An LT1397 can be used to create buffered color-differ-

ence signals from RGB inputs (Figure 4). In this applica-

tion, the R input arrives via 75

Ω coax. It is routed to the

noninverting input of LT1397 amplifier A1 and to a 845

Ω

resistor R8. There is also an 82.5

Ω termination resistor

R11, which yields a 75

Ω input impedance at the R input

when considered in parallel with R8. R8 connects to the

inverting input of a second LT1397 amplifier (A2), which

also sums the weighted G and B inputs to create a

–0.5 • Y output. LT1397 amplifier A3 then takes the

–0.5 • Y output and amplifies it by a gain of –2, resulting

in the Y output. Amplifier A1 is configured in a noninvert-

ing gain of 2 with the bottom of the gain resistor R2 tied

to the Y output. The output of amplifier A1 thus results in

the color-difference output R-Y.

The B input is similar to the R input. It arrives via 75

Ω

coax, and is routed to the noninverting input of LT1397

amplifier A4, and to a 2320

Ω resistor R10. There is also

a 76.8

Ω termination resistor R13, which yields a 75Ω

Figure 4. Buffered RGB to Color-Difference Matrix

A2

1/4 LT1397

A3

1/4 LT1397

–

+

A1

1/4 LT1397

R7

255

Ω

R6

127

Ω

R5

255

Ω

R10

2320

Ω

R9

432

Ω

R11

82.5

Ω

R

G

B

R12

90.9

Ω

R13

76.8

Ω

ALL RESISTORS 1%

R8

845

Ω

75

Ω

SOURCES

R1

255

Ω

R2

255

Ω

R4

255

Ω

R3

255

Ω

B-Y

Y

R-Y

1395/6/7 F04

A4

1/4 LT1397