LT1223 Linear Technology, LT1223 Datasheet - Page 8

• Manufacturer Part Number: LT1223
• Description: 100MHz Current Feedback Amplifier
• Manufacturer: Linear Technology

LT1223
O
U
U
W
U
A
PPLICATI
S
I FOR ATIO
Shutdown
Output Slew Rate of 500V/ s
Pin 8 activates a shutdown control function. Pulling more
than 200 A from pin 8 drops the supply current to less than
3mA, and puts the output into a high impedance state. The
easy way to force shutdown is to ground pin 8, using an
open collector (drain) logic stage. An internal resistor limits
current, allowing direct interfacing with no additional parts.
When pin 8 is open, the LT1223 operates normally.
Slew Rate
The slew rate of a current feedback amplifier is not inde-
pendent of the amplifier gain configuration the way it is in
a traditional op amp. This is because the input stage and
the output stage both have slew rate limitations. Inverting
amplifiers do not slew the input and are therefore limited
Output Slew Rate of 1000V/ s
only by the output stage. High gain, noninverting amplifi-
ers are similar. The input stage slew rate of the LT1223 is
about 350V/ s before it becomes nonlinear and is en-
hanced by the normally reverse-biased emitters on the
input transistors. The output slew rate depends on the size
of the feedback resistors. The peak output slew rate is
about 2000V/ s with a 1k feedback resistor and drops
proportionally for larger values. At an output slew rate of
1000V/ s or more, the transistors in the “mirror circuits”
will begin to saturate due to the large feedback currents.
This causes the output to have slew induced overshoot and
is somewhat unusual looking; it is in no way harmful or
dangerous to the device. The photos show the LT1223 in
a noninverting gain of three (R
= 1k, R
= 500 ) with a
F
G
Output Slew Rate at 2000V/ s Shows Aberrations (See Text)
20V peak-to-peak output slewing at 500V/ s, 1000V/ s
and 2000V/ s.
Settling Time
The Inverting Amplifier Settling Time versus Output Step
curve shows that the LT1223 will settle to within 1mV of
final value in less than 100ns for all output changes of 10V
or less. When operated as an inverting amplifier there is
less than 500 V of thermal settling in the amplifier.
However, when operating the LT1223 as a noninverting
amplifier, there is an additional thermal settling compo-
nent that is about 200 V for every volt of input common
mode change. So a noninverting gain of one amplifier will
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