LT1637 Linear Technology, LT1637 Datasheet - Page 9

• Manufacturer Part Number: LT1637
• Description: 1.1MHz/ 0.4V/us Over-The-Top Micropower/ Rail-To-Rail Input and Output Op Amp
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
A Schottky diode in the collector of each NPN transistor of
the NPN input stage allows the LT1637 to operate with
either or both of its inputs above V
V
bias current is typically 23 A at room temperature. The
input offset voltage is typically 600 V when operating
above V
V
The inputs are protected against excursions as much as
22V below V
each input and a diode from the input to the negative
supply. There is no output phase reversal for inputs up to
5V below V
inputs and the maximum differential input voltage is 44V.
Output
The output voltage swing of the LT1637 is affected by
input overdrive as shown in the typical performance
curves. When monitoring input voltages within 100mV of
V
The output of the LT1637 can be pulled up to 25V beyond
V
is less than 0.5V.
The normally reverse biased substrate diode from the
output to V
output is forced below V
limited to 100mA, no damage will occur.
The LT1637 is internally compensated to drive at least
200pF of capacitance under any output loading condi-
tions. A 0.22 F capacitor in series with a 150 resistor
between the output and ground will compensate these
amplifiers for larger capacitive loads, up to 4700pF, at all
output currents.
Distortion
There are two main contributors of distortion in op amps:
output crossover distortion as the output transitions from
sourcing to sinking current and distortion caused by
nonlinear common mode rejection. Of course, if the op
amp is operating inverting there is no common mode
induced distortion. When the LT1637 switches between
input stages there is significant nonlinearity in the CMRR.
+
–
+
+
, gain should be taken to keep the output from clipping.
the NPN input transistor is fully saturated and the input
with less than 1nA of leakage current, provided that V
regardless of V
+
. The LT1637 will operate with its input 44V above
–
–
will cause unlimited currents to flow when the
. There are no clamping diodes between the
–
by an internal 1.3k resistor in series with
+
U
.
–
. If the current is transient and
U
+
. At about 0.3V above
W
U
+
Lower load resistance increases the output crossover
distortion, but has no effect on the input stage transition
distortion. For lowest distortion the LT1637 should be
operated single supply, with the output always sourcing
current and with the input voltage swing between ground
and (V
istics curves.
Gain
The open-loop gain is less sensitive to load resistance
when the output is sourcing current. This optimizes per-
formance in single supply applications where the load is
returned to ground. The typical performance photo of
Open-Loop Gain for various loads shows the details.
Shutdown
The LT1637 can be shut down two ways: using the
shutdown pin or bringing V
is brought to within 0.5V of V
output leakage current drop to less than 10nA. When the
shutdown pin is brought 1.2V above V
current drops to about 3 A and the output leakage current
is less than 1 A, independent of V
bias current is less than 0.1nA (even if the inputs are 44V
above the negative supply).
The shutdown pin can be taken up to 32V above V
shutdown pin can be driven below V
current through the substrate diode should be limited with
an external resistor to less than 10mA.
Input Offset Nulling
The input offset voltage can be nulled by placing a 10k
potentiometer between Pins 1 and 8 with its wiper to V
(see Figure 1). The null range will be at least 3mV.
+
– 0.9V). See the Typical Performance Character-
Figure 1. Input Offset Nulling
LT1637
1
+
10k
V
to within 0.5V of V
–
–
both the supply current and
8
+
. In either case the input
1637 F01
–
, however the pin
–
LT1637
, the supply
–
. When V
–
. The
9
+
–