Datasheet

LTC1052/LTC7652
12
1052fa
OUTPUT CLAMP
If the LTC1052 is driven into saturation, the nulling loop,
attempting to force the differential input voltage to zero,
will drive C
EXTA
and C
EXTB
to a supply rail. After the
saturating drive is removed, the capacitors take a finite
time to recover—this is the overload recovery time. The
overload recovery is longest when the capacitors are
driven to the negative rail (refer to Overload Recovery in
the Typical Performance Characteristics section). The
overload recovery time in this case is typically 225ms. In
the opposite direction (i.e., C
EXTA
and C
EXTB
at positive
rail), it is about ten times faster (25ms). The overload
recovery time for the LTC1052 is much faster than com-
petitive devices; however, if a faster overload recovery
time is necessary, the output clamp function can be used.
When the output clamp is connected to the negative input
it prevents the amplifier from saturating, thus keeping
C
EXTA
and C
EXTB
at their nominal voltages. The output
clamp is a switch that turns on when the output gets to
APPLICATIO S I FOR ATIO
WUUU
within approximately 1V of either supply rail. This switch
is in parallel with the amplifier’s feedback resistor. As the
output moves closer to the rail, the switch on
resistance decreases, reducing the closed loop gain. The
output swing is reduced when the clamp function is used.
How much current the output clamp leaks when off
is important because, when used, it is connected to the
amplifier’s negative input. Any current acts like input bias
current and will degrade accuracy. At the other extreme,
the maximum current the clamp conducts when on deter-
mines how much overdrive the clamp will take, and still
keep the amplifier from saturating. Both of these numbers
are guaranteed in the Electrical Characteristics section.
LOW SUPPLY OPERATION
The minimum supply voltage for proper operation of the
LTC1052 is typically 4.0V (±2.0V). In single supply
applications, PSRR is guaranteed down to 4.7V (±2.35V).
This assures proper operation down to the minimum TTL
specified voltage of 4.75V.
TYPICAL APPLICATIO S
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5V Powered Ultraprecision Instrumentation Amplifier Fast Precision Inverter
LTC1052/7652 • TA04
8pF
–5V
1N4148
10k*
1000pF
5V
5V
300pF
7
0.1µF
*1% METAL FILM
INPUT
0.1µF
2
3
10k
–5V
OUTPUT
4
6
10k
2
6
8
4
1
10k
7
3
FULL POWER BANDWIDTH = 2MHz
SLEW RATE = 40V/µs
SETTLING (10V STEP) = 12µs TO 0.01%
BIAS CURRENT DC = 30pA
OFFSET DRIFT = 50nV/°C
OFFSET VOLTAGE = 5µV
10k*
+
–
LT318A
+
–
LTC1052
LTC1052/7652 • TA03
6
C2
+IN
V
OUT
5V
5V
0.1µF
LTC1043
C1
43k
0.22µF
R2
100k
–IN
1N914
0.0047µF
5V
7
R1
100
≈ – 0.5V
CIRCUITRY WITHIN DASHED LINES MAY BE DELETED IF OUTPUT
DOES NOT HAVE TO SWING ALL THE WAY TO GROUND
1µF1µF
15
12
4
7
13
C3
1µF
C4
1µF
5
16
17
18
3
2
8
3
2
4
0.1µF
1
10k
DRIFT = 50nV/°C
V
OS
= 3µV
GAIN =
CMRR = >120dB DC – 20kHz
BANDWIDTH = 10Hz
R2
R1
+ 1
8
+
–
LTC1052
11
14
6
+