Driving Capacitive Loads

When driving loads greater than 100pF, you may need

a capacitance compensating resistor in series with the

output of each affected amplifier. The required resistor

will depend on load as well as capacitance. For 150

Ω

or higher load resistances and capacitance up to

1000pF, use a 2.4

Ω resistor. For 100Ω loads, use a

4.7

Ω resistor.

If an output amplifier is loaded with a pure capacitance

or with the inputs of other MAX458/MAX459s, the resis-

tors will cause no degradation of gain or other perfor-

mance because of the high impedance of the

crosspoints. However, resistive loads may cause a

reduction in gain.

Daisy-Chaining Devices

The serial output, DOUT, allows cascading of two or

more crosspoint switches to create larger arrays. The

data at DOUT is the DIN data delayed by 16 cycles

plus one clock width. DOUT changes on SCLK’s falling

edge when

–

C

—

S

–

is low. When C

—

S

–

is high, DOUT remains

in the state of the last data bit.

Any number of MAX458/MAX459 crosspoint switches

can be daisy-chained by connecting the DOUT of one

device to the DIN of the next device in the chain, as

shown in Figure 12. For proper timing, ensure that both

—

S

–

DOUT is a TTL-compatible output with an active pull-

up. It does not become high impedance when C

—

S

–

is

high.

8x4 Video Crosspoint Switches with Buffers

14

______________________________________________________________________________________

MAX458

MAX459

MAX458

MAX459

CS

SCLK

DOUT

DIN

DOUT

SERIAL

DATA

INPUT

1

20

40

39

28

30

32

34

1

20

40

39

28

30

32

34

OUT3

OUT2

OUT1

OUT0

Figure 12. 16x4 Crosspoint Switch Using Serial "Daisy Chain"

Connection