LT1259/LT1260
APPLICATIO S I FOR ATIO
The input slew rate of the LT1259/LT1260 is approxi-
mately 270V/µs and is set by internal currents and capaci-
tances. The output slew rate is set by the value of the
feedback resistors and internal capacitances. At a gain of
10 with at 1k feedback resistor and
±15V
supplies, the
output slew rate is typically 1600V/µs. Larger feedback
resistors will reduce the slew rate as will lower supply
voltages, similar to the way the bandwidth is reduced.
The graph of Maximum Undistorted Output vs Frequency
relates the slew rate limitations to sinusoidal input for
various gains.
Large-Signal Transient Response, A
V
= 2
V
S
=
±15V
R
F
= R
G
= 1.6k
R
L
= 400Ω
LT1259/LT1260 • AI01
Large-Signal Transient Response, A
V
= 10
V
S
=
±15V
R
F
= 1k
R
G
= 110Ω
R
L
= 400Ω
LT1259/LT1260 • AI02
Enable/Disable
The LT1259/LT1260 amplifiers have a unique high imped-
ance, zero supply current mode which is controlled by
independent EN pins. When disabled, an amplifier output
8
U
looks like a 4.4pF capacitor in parallel with a 75k resistor,
excluding feedback resistor effects. These amplifiers are
designed to operate with open drain logic: the EN pins have
internal pullups and the amplifiers draw zero current when
these pins are high. To activate an amplifier, its EN pin is
pulled to ground (or at least 2V below the positive supply).
The enable pin current is approximately 60µA when
activated. Input referred switching transients with no
input signal applied are only 35mV positive and 80mV
negative with R
L
= 100Ω.
Output Switching Transient
EN
OUTPUT
V
S
=
±5V
V
IN
= 0V
R
F
= R
G
= 1.6k
R
L
= 100Ω
LT1259/LT1260 • AI03
W
U U
The enable/disable times are very fast when driven from
standard 5V logic. The amplifier enables in about 100ns
(50% point to 50% point) while operating on
±5V
sup-
plies. Likewise the disable time is approximately 40ns
(50% point to 50% point) or 75ns to 90% of the final
value. The output decay time is set by the output capaci-
tance and load resistor.
Amplifier Enable Time, A
V
= 10
OUTPUT
EN
V
S
=
±5V
V
IN
= 0.1V
R
F
= 1k
R
G
= 110Ω
R
L
= 150Ω
LT1259/LT1260 • AI04
LINER [ LINEAR TECHNOLOGY ]
