OPA355 datasheet(11/27 Pages) TI

11 / 27 page

OPA355, 2355, 3355

SBOS195D

www.ti.com

The Enable input can be modeled as a CMOS input gate with

a 100k

Ω pull-up resistor to V+. Left open, the Enable pin will

assume a logic HIGH, and the amplifier will be on.

The Enable time is 100ns and the disable time is only 30ns.

This allows the OPA355 to be operated as a “gated” amplifier,

or to have its output multiplexed onto a common output bus.

When disabled, the output assumes a high-impedance state.

OUTPUT DRIVE

The output stage can supply high short-circuit current (typi-

cally over 200mA). Therefore, an on-chip thermal shutdown

circuit is provided to protect the OPA355 from dangerously

high junction temperatures. At 160

°C, the protection circuit

will shut down the amplifier. Normal operation will resume

when the junction temperature cools to below 140

°C.

NOTE: it is not recommended to run a continuous DC current

in excess of

±60mA. Refer to the Typical Characteristics,

Output Voltage Swing vs Output Current.

VIDEO

The OPA355 output stage is capable of driving a standard

back-terminated 75

Ω video cable. By back-terminating a

transmission line, it does not exhibit a capacitive load to its

driver. A properly back-terminated 75

Ω cable does not ap-

pear as capacitance; it presents only a 150

Ω resistive load to

the OPA355 output.

The OPA355 can be used as an amplifier for RGB graphic

signals, which have a voltage of zero at the video black

level, by offsetting and AC-coupling the signal, as shown in

Figure 1.

WIDEBAND VIDEO MULTIPLEXING

One common application for video speed amplifiers which

include an enable pin is to wire multiple amplifier outputs

together, then select which one of several possible video

inputs to source onto a single line. This simple

Wired-OR

Video Multiplexer can be easily implemented using the

OPA357; see Figure 2.

INPUT AND ESD PROTECTION

All OPA355 pins are static protected with internal ESD

protection diodes tied to the supplies; see Figure 3.

These diodes will provide overdrive protection if the current

is externally limited to 10mA by the source or by a resistor.

FIGURE 1. RGB Cable Driver.

1/3

OPA355

604

Ω

µF

10nF

+3V

Ω

Red

Green

Blue

604

Ω

Red(1)

V+

Green(1)

V+

Blue(1)

V+

Ω

220

µF

604

Ω

1/3

OPA355

1/3

OPA355

604

Ω

604

Ω

604

Ω

NOTE: (1) Source video signal offset 300mV above ground

to accommodate op amp swing-to-ground capability.

220

µF

220

µF

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