9

LT1210

S

APPLICATI

I FOR ATIO

Figure 2. Shutdown Interface

–

+

LT1210

SD

15V

–15V

5V

24k

ENABLE

1210 F02

15V

74C906

up the turn-off time and ensures that the LT1210 is

completely turned off. Because the pin is referenced to

the positive supply, the logic used should have a break-

down voltage of greater than the positive supply voltage.

No other circuitry is necessary as the internal circuit

limits the Shutdown pin current to about 500

µA. Figure

3 shows the resulting waveforms.

Figure 3. Shutdown Operation

1210 F03

For applications where the full bandwidth of the amplifier

is not required, the quiescent current of the device may be

reduced by connecting a resistor from the Shutdown pin

to ground. The quiescent current will be approximately 65

times the current in the Shutdown pin. The voltage across

82k resistor will set the quiescent supply current to 9mA

The photos in Figures 4a and 4b show the effect of

reducing the quiescent supply current on the large-signal

response. The quiescent current can be reduced to 9mA in

the inverting configuration without much change in re-

sponse. In noninverting mode, however, the slew rate is

reduced as the quiescent current is reduced.

1210 F04a

1210 F04b

Slew Rate

Unlike a traditional op amp, the slew rate of a current

feedback amplifier is not independent of the amplifier gain

configuration. There are slew rate limitations in both the

input stage and the output stage. In the inverting mode,

and for higher gains in the noninverting mode, the signal

amplitude on the input pins is small and the overall slew

rate is that of the output stage. The input stage slew rate

is related to the quiescent current and will be reduced as

the supply current is reduced. The output slew rate is set

by the value of the feedback resistors and the internal

capacitance. Larger feedback resistors will reduce the

slew rate as will lower supply voltages, similar to the way