LT1498IS8 Linear Technology, LT1498IS8 Datasheet - Page 14

• Manufacturer Part Number: LT1498IS8
• Description: IC,Operational Amplifier,DUAL,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Linear Technology

LT1498/LT1499
APPLICATIONS INFORMATION
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 475μV. To maintain the precision
characteristics of the amplifi er, the change of V
entire input common mode range (CMRR) is guaranteed
to be less than 425μV 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 sec-
tion. When the PNP differential pair is active, the input bias
currents fl ow out of the input pins; they fl ow 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
14
+IN
–IN
V
V
+
–
R6
R7
D5
D6
Q4
Q7
D1
D2
Q3
Figure 1. LT1498 Simplifi ed Schematic Diagram
Q5
Q6
OS
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 amplifi er 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 (700Ω total) limit the input current for differential
input signals of 7V or less. For larger input levels, a re-
sistor 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 amplifi er is protected against ESD strikes up
to 3kV on all pins.
Capacitive Load
The LT1498/LT1499 are designed for ease of use. The
amplifi er can drive a capacitive load of more than 10nF
Q10
Q11
Q9
R3
R1
Q12
Q8
R2
R4
V
Q13
–
R5
OUTPUT BIAS
C
C
BUFFER
AND
C2
C1
14989 F01
Q15
Q14
OUT
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