Datasheet

TC7652
DS21464C-page 8  2001-2012 Microchip Technology Inc.
4.6 Pin Compatibility
Where possible, the 8-pin device pinout conforms to
such industry standards as the LM101 and LM741. Null
storing external capacitors connect to Pins 1 and 8,
which are usually for offset null or compensation capac-
itors. Output clamp (Pin 5) is similarly used. For OP05
and OP07 devices, replacement of the offset null
potentiometer (connected between Pins 1 and 8 and
V
DD
by two capacitors from those pins to V
SS
) provides
compatibility. Replacing the compensation capacitor
between Pins 1 and 8 by two capacitors to V
SS
is
required. The same operation (with the removal of any
connection to Pin 5) works for LM101, A748 and sim-
ilar parts.
Because NC pins provide guarding between input and
other pins, the 14-pin device pinout conforms closely to
the LM108. Because this device does not use any extra
pins and does not provide offset nulling (but requires a
compensation capacitor), some layout changes are
necessary to convert to the TC7652.
4.7 Some Applications
Figures 4-2 and 4-3 show basic inverting and nonin-
verting amplifier circuits using the output clamping cir-
cuit to enhance overload recovery performance. The
only limitations on replacing other op amps with the
TC7652 are supply voltage (±8V maximum) and output
drive capability (10k load for full swing). Overcome
these limitations with a booster circuit (Figure 4-4) to
combine output capabilities of the LM741 (or other
standard device) with input capabilities of the TC7652.
These two form a composite device, therefore, when
adding the feedback network, the monitor loop gains
stability.
FIGURE 4-2: NONINVERTING
AMPLIFIER WITH
OPTIONAL CLAMP
FIGURE 4-3: INVERTING AMPLIFIER
WITH OPTIONAL CLAMP
FIGURE 4-4: USING 741 TO BOOST
OUTPUT DRIVE
CAPABILITY
Figure 4-5 shows the clamp circuit of a zero offset com-
parator. Because the clamp circuit requires the invert-
ing input to follow the input signal, problems with a
chopper stabilized op amp are avoided. The threshold
input must tolerate the output clamp current V
IN
/R
without disrupting other parts of the system.
Figure 4-6 shows how the TC7652 can offset null high
slew rate and wideband amplifiers.
Mixing the TC7652 with circuits operating at ±15V
requires a lower supply voltage divider with the TC7660
voltage converter circuit operated "backwards." Figure
4-7 shows an approximate connection.
FIGURE 4-5: LOW OFFSET
COMPARATOR
TC7652
+
–
Output
Clamp
Input
0.1µF
R
2
R
1
R
3
0.1µF
+
–
Output
Input
R
2
R
1
Clamp
0.1µF 0.1µF
TC7652
+
–
+
–
+15V
-15V
-7.5V
0.1
µF
In
Out
-7.5V
0.1
µF
10kΩ
TC7652
741
TC7652
+
–
V
OUT
Clamp
V
IN
0.1µF 0.1µF
200kΩ to 2mΩ
V
TH