Datasheet

LM611
SNOSC08C –MAY 1998–REVISED MARCH 2013 www.ti.com
OPERATIONAL AMPLIFIER
The amp or the reference may be biased in any way with no effect on the other, except when a substrate diode
conducts (see
(1)
under Electrical Characteristics). The amp may have inputs outside the common-mode range,
may be operated as a comparator, or have all terminals floating with no effect on the reference (tying inverting
input to output and non-inverting input to V
−
on unused amp is preferred). Choosing operating points that cause
oscillation, such as driving too large a capacitive load, is best avoided.
Op Amp Output Stage
The op amp, like the LM124 series, has a flexible and relatively wide-swing output stage. There are simple rules
to optimize output swing, reduce cross-over distortion, and optimize capacitive drive capability:
1. Output Swing: Unloaded, the 42 μA pull-down will bring the output within 300 mV of V
−
over the military
temperature range. If more than 42 μA is required, a resistor from output to V
−
will help. Swing across any
load may be improved slightly if the load can be tied to V
+
, at the cost of poorer sinking open-loop voltage
gain.
2. Cross-over Distortion: The LM611 has lower cross-over distortion (a 1 V
BE
deadband versus 3 V
BE
for the
LM124), and increased slew rate as shown in the Typical Performance Charactersitics curves. A resistor pull-
up or pull-down will force class-A operation with only the PNP or NPN output transistor conducting,
eliminating cross-over distortion.
3. Capacitive Drive: Limited by the output pole caused by the output resistance driving capacitive loads, a pull-
down resistor conducting 1 mA or more reduces the output stage NPN r
e
until the output resistance is that of
the current limit 25Ω. 200 pF may then be driven without oscillation.
Op Amp Input Stage
The lateral PNP input transistors, unlike those of most op amps, have BV
EBO
equal to the absolute maximum
supply voltage. Also, they have no diode clamps to the positive supply nor across the inputs. These features
make the inputs look like high impedances to input sources producing large differential and common-mode
voltages.
Typical Applications
*10k must be low
t.c. trim pot.
Figure 64. Ultra Low Noise 10.00V Reference.
Total Output Noise is Typically 14 μV
RMS
.
Adjust the 10k pot for 10.000V.
(1) Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply
when operating the device beyond its rated operating conditions.
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