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LT1210

1.1A, 35MHz Current Feedback Amplifier

Linear Technology 

LT1210

APPLICATI S I FOR ATIO

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

5c show the large-signal response of the LT1210 for

various gain configurations. The slew rate varies from

770V/µs for a gain of 1, to 1100V/µs for a gain of – 1.

When the LT1210 is used to drive capacitive loads, the

available output current can limit the overall slew rate. In

the fastest configuration, the LT1210 is capable of a slew

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

at this rate is 1mA per picofarad of capacitance, so

10,000pF would require 10A! The photo (Figure 6) shows

the large-signal behavior with CL = 10,000pF. The slew

rate is about 150V/µs, determined by the current limit of

1.5A.

RF = 825Ω

RL = 10Ω

VS = ±15V

1210 F05a

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

RF = RG = 750Ω VS = ±15V

RL = 10Ω

1210 F05b

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

RF = RG = 750Ω

RL = 10Ω

VS = ±15V

1210 F05c

Figure 5c. Large-Signal Response, AV = 2

10

RF = RG = 3k

RL = ∞

VS = ±15V

1210 F06

Figure 6. Large-Signal Response, CL = 10,000pF

Differential Input Signal Swing

The differential input swing is limited to about ±6V by an

ESD protection device connected between the inputs. In

normal operation, the differential voltage between the

input pins is small, so this clamp has no effect; however,

in the shutdown mode the differential swing can be the

same as the input swing. The clamp voltage will then set

the maximum allowable input voltage. To allow for some

margin, it is recommended that the input signal be less

than ±5V when the device is shut down.

Capacitance on the Inverting Input

Current feedback amplifiers require resistive feedback

from the output to the inverting input for stable operation.

Take care to minimize the stray capacitance between the

output and the inverting input. Capacitance on the invert-

ing input to ground will cause peaking in the frequency

response (and overshoot in the transient response), but it

does not degrade the stability of the amplifier.

1210fa

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