Datasheet

®
OPA121
5
–15 –10 –5 0 +5 +10 +15
Input Voltage (V)
–2
+2
+1
–1
Input Current (mA)
INPUT CURRENTS vs INPUT VOLTAGE
WITH ±V PINS GROUNDED
0
CC
I
IN
V
Maximum Safe Current
Maximum Safe Current
APPLICATIONS INFORMATION
OFFSET VOLTAGE ADJUSTMENT
The OPA121 offset voltage is laser-trimmed and will require
no further trim for most applications. As with most ampli-
fiers, externally trimming the remaining offset can change
drift performance by about 0.3µV/°C for each 100µV of
adjusted offset. Note that the trim (Figure 1) is similar to
operational amplifiers such as 741 and AD547. The OPA121
can replace most BIFET amplifiers by leaving the external
null circuit unconnected.
*
7
6
2
3
4
5
1
±10mV Typical
Trim Range
*10k to 1M
Trim Potentiometer
(100k Recommended)
Ω
Ω
Ω
+V
CC
–V
CC
OPA121
FIGURE 1. Offset Voltage Trim.
INPUT PROTECTION
Conventional monolithic FET operational amplifiers require
external current-limiting resistors to protect their inputs
against destructive currents that can flow when input FET
gate-to-substrate isolation diodes are forward-biased. Most
BIFET amplifiers can be destroyed by the loss of –V
CC
.
Unlike BIFET amplifiers, the
Difet OPA121 requires input
current limiting resistors only if its input voltage is greater
than 6V more negative than –V
CC
. A 10kΩ series resistor
will limit input current to a safe level with up to ±15V input
levels even if both supply voltages are lost.
Static damage can cause subtle changes in amplifier input
characteristics without necessarily destroying the device. In
precision operational amplifiers (both bipolar and FET types),
TYPICAL PERFORMANCE CURVES (CONT)
T
A
= +25°C, V
CC
= ±15VDC unless otherwise noted.

SMALL SIGNAL TRANSIENT RESPONSE
Time(µs)
01 2 3 45
0
Output Voltage (mV)
+80
+80
+40
+40

LARGE SIGNAL TRANSIENT RESPONSE
Time(µs)
02550
+15
0
-15
Output Voltage (V)