9

LT1229/LT1230

Assumptions:

1. The maximum ambient is 70

°C for the commercial

parts (C suffix) and 125

°C for the full temperature

parts (M suffix).

2. The load is a double-terminated video cable, 150

Ω.

3. The maximum output voltage is 2V (peak or DC).

4. The thermal resistance of each package:

J8 is 100

°C/W

J is 80

°/W

N8 is 100

°C/W

N is 70

°/W

S8 is 150

°C/W

S is 110

°/W

Maximum Supply Voltage for 75

Ω Cable Driving Applications at

Maximum Ambient Temperature

PART

PACKAGE

MAX SUPPLY

LT1229MJ8

Ceramic DIP

0.500W @ 125

LT1229CJ8

Ceramic DIP

1.050W @ 70

LT1229CN8

Plastic DIP

0.800W @ 70

LT1229CS8

Plastic SO8

0.533W @ 70

LT1230MJ

Ceramic DIP

0.625W @ 125

LT1230CJ

Ceramic DIP

1.313W @ 70

LT1230CN

Plastic DIP

1.143W @ 70

LT1230CS

Plastic SO14

0.727W @ 70

Slew Rate

The slew rate of a current feedback amplifier is not

independent of the amplifier gain the way it is in a tradi-

tional op amp. This is because the input stage and the

output stage both have slew rate limitations. The input

stage of the LT1229/LT1230 amplifiers slew at about

100V/

µs before they become nonlinear. Faster input sig-

nals will turn on the normally reverse-biased emitters on

the input transistors and enhance the slew rate signifi-

cantly. This enhanced slew rate can be as much as

2500V/

µs.

The output slew rate is set by the value of the feedback

resistors and the internal capacitance. At a gain of ten with

a 1k feedback resistor and

±15V supplies, the output slew

rate is typically 700V/

µs and –1000V/µs. There

is no input stage enhancement because of the high gain.

S

APPLICATI

I FOR ATIO

LT1229 • TA07

Settling Time

The characteristic curves show that the LT1229/LT1230

amplifiers settle to within 10mV of final value in 40ns to

55ns for any output step up to 10V. The curve of settling

to 1mV of final value shows that there is a slower thermal

contribution up to 20

µs. The thermal settling component

comes from the output and the input stage. The output

contributes just under 1mV per volt of output change and

the input contributes 300

µV per volt of input change.

Fortunately, the input thermal tends to cancel the output

thermal. For this reason the noninverting gain of two

configurations settles faster than the inverting gain of one.

Larger feedback resistors will reduce the slew rate as will

lower supply voltages, similar to the way the bandwidth is

reduced.

LT1229 • TA08