LT1206CS8 datasheet(10/16 Pages) LINER

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LT1206

APPLICATI

I FOR ATIO

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

the bandwidth is reduced. The photos (Figures 5a, 5b and

5c) show the large-signal response of the LT1206 for

various gain configurations. The slew rate varies from

860V/

µs for a gain of 1, to 1400V/µs for a gain of –1.

LT1206 • F05a

RF = 825Ω

RL = 50Ω

VS = ±15V

Figure 5a. Large-Signal Response, AV = 1

Figure 5b. Large-Signal Response, AV = –1

LT1206 • F05b

RF = RG = 750Ω

RL = 50Ω

VS = ±15V

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 40

times the current in the shutdown pin. The voltage across

the resistor in this condition is V+ – 3VBE. For example, a

60k resistor will set the quiescent supply current to 10mA

with VS = ±15V.

The photos (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 5mA in the

inverting configuration without much change in response.

In noninverting mode, however, the slew rate is reduced

as the quiescent current is reduced.

LT1206 • F04a

RF = 750Ω

RL = 50Ω

IQ = 5mA, 10mA, 20mA

VS = ±15V

LT1206 • F04b

RF = 750Ω

RL = 50Ω

IQ = 5mA, 10mA, 20mA

VS = ±15V

Figure 4b. Large-Signal Response vs IQ, AV = 2

Figure 4a. Large-Signal Response vs IQ, AV = –1

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