LT1499 LINER [Linear Technology], LT1499 Datasheet - Page 12

• Manufacturer Part Number: LT1499
• Description: 10MHz, 6V/us, Dual/Quad Rail-to-Rail Input and Output Precision C-Load Op Amps
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
LT1498/LT1499
12
Input Offset Voltage
The offset voltage changes depending upon which input
stage is active. The input offsets are random, but are
trimmed to less than 475 V. To maintain the precision
characteristics of the amplifier, the change of V
entire input common mode range (CMRR) is guaranteed
to be less than 425 V on a single 5V supply.
Input Bias Current
The input bias current polarity also depends on the input
common mode voltage, as described in the previous
section. When the PNP differential pair is active, the input
bias currents flow out of the input pins; they flow in
opposite direction when the NPN input stage is active. The
offset error due to input bias current can be minimized by
equalizing the noninverting and inverting input source
impedances. This will reduce the error since the input
offset currents are much less than the input bias currents.
Overdrive Protection
To prevent the output from reversing polarity when the
input voltage exceeds the power supplies, two pair of
crossing diodes D1 to D4 are employed. When the input
+ IN
– IN
V
V
+
–
R6
R7
D5
U
D6
INFORMATION
U
Q4
Q7
D1
D2
Q3
W
Figure 1. LT1498 Simplified Schematic Diagram
Q5
Q6
OS
U
V
BIAS
over the
Q1
D3
D4
Q2
I
1
voltage exceeds either power supply by approximately
700mV, D1/D2 or D3/D4 will turn on, forcing the output to
the proper polarity. For the phase reversal protection to
work properly, the input current must be less than 5mA. If
the amplifier is to be severely overdriven, an external
resistor should be used to limit the overdrive current.
Furthermore, the LT1498/LT1499’s input stages are pro-
tected by a pair of back-to-back diodes, D5/D6. When a
differential voltage of more than 0.7V is applied to the
inputs, these diodes will turn on, preventing the Zener
breakdown of the input transistors. The current in D5/D6
should be limited to less than 10mA. Internal resistors R6
and R7 (700 total) limit the input current for differential
input signals of 7V or less. For larger input levels, a
resistor in series with either or both inputs should be
used to limit the current. Worst-case differential input
voltage usually occurs when the output is shorted to
ground. In addition, the amplifier is protected against
ESD strikes up to 3kV on all pins.
Capacitive Load
The LT1498/LT1499 are designed for ease of use. The
amplifier can drive a capacitive load of more than 10nF
Q10
Q11
Q9
R3
R1
Q12
Q8
R4
R2
V
Q13
–
R5
OUTPUT BIAS
C
C
BUFFER
AND
C2
C1
Q15
Q14
1498/99 F01
OUT