LT1207CS datasheet(10/16 Pages) LINER

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LT1207

APPLICATI

I FOR ATIO

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 LT1207 or

various gain configurations. The slew rate varies from

860V/

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

When the LT1207 is used to drive capacitive loads, the

available output current can limit the overall slew rate. In

the fastest configuration, the LT1207 is capable of a slew

rate of over 1V/ns. The current required to slew a capacitor

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

LT1207 • F05b

RF = RG = 750Ω

RL = 50Ω

VS = ±15V

The amplifier’s supply 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 amplifier’s 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.

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

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

LT1207 • F04a

RF = 750Ω

RL = 50Ω

IQ = 5mA, 10mA, 20mA

VS = ±15V

LT1207 • F04b

RF = 750Ω

RL = 50Ω

IQ = 5mA, 10mA, 20mA

VS = ±15V

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,

LT1207 • F05a

RF = 825Ω

RL = 50Ω

VS = ±15V

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

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