TC7652
LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER
1
FEATURES
■ Low Offset Over Temperature Range ............ 10µV
■ Ultra-Low Long-Term Drift .................150nV/Month
■ Low Temperature Drift ............................. 100nV/°C
■ Low DC Input Bias Current ............................. 15pA
■ High Gain, CMRR and PSRR ................. 110dB Min
■ Low Input Noise Voltage .........0.2µV
■ Internally-Compensated for Unity-Gain Operation
■ Clamp Circuit for Fast Overload Recovery
PIN CONFIGURATIONS
C
1
B
C
2
A
NC
3
–INPUT
4
TC7652CPD
5
+INPUT
6
NC
7
V
SS
NC = NO INTERNAL CONNECTION
(MAY BE USED AS INPUT GUARD)
14
13
12
11
10
9
8
INT/EXT
EXT CLK
IN
INT CLK
OUT
V
DD
OUTPUT
OUTPUT
CLAMP
C
RET
C
–INPUT
+INPUT
V
1
A
2
3
4
SS
; DC to 1Hz
P-P
TC7652CPA
8
7
6
5
C
B
V
DD
OUTPUT
CLAMP
GENERAL DESCRIPTION
The TC7652 is a lower noise version of the TC7650,
sacrificing some input specifications (bias current and bandwidth) to achieve a 10x reduction in noise. All the other
benefits of the chopper technique are present, i.e. freedom
from offset adjust, drift, and reliability problems from external trim components. Like the TC7650, the TC7652 requires only two noncritical external caps for storing the
chopped null potentials. There are no significant chopping
spikes, internal effects or overrange lockup problems.
ORDERING INFORMATION
Temperature
Part No. Package Range
TC7652CPA 8-Pin Plastic DIP 0°C to +70°C
TC7652CPD 14-Pin Plastic DIP 0°C to +70°C
2
3
4
FUNCTIONAL BLOCK DIAGRAM
OUTPUT CLAMP
(NOT ON "Z" PINOUT)
INPUTS
TELCOM SEMICONDUCTOR, INC.
OUTPUT CLAMP
CIRCUIT
MAIN
AMPLIFIER
NULL
INTERMOD
COMPARATOR
BB
NULL
AMPLIFIER
A
NULL
NOTE: 1. For 8-pin DIP connect to VSS, or to C
OSCILLATOR
BA
on "Z" pinout.
RET
5
TC7652
14-PIN DIP ONLY
INT/EXT
EXT CLK IN
CLK OUT
BA
C
EXT
OUTPUT
6
7
C
EXT
C
(NOTE 1)
RET
V
SS
8
TC7652-7 9/11/96
3-281
TC7652
LOW NOISE, CHOPPER-ST ABILIZED
OPERATIONAL AMPLIFIER
ABSOLUTE MAXIMUM RATINGS
Total Supply Voltage (VDD to VSS) ........................... +18V
Input Voltage ........................ (V
Voltage on Oscillator Control Pins ...................VDD to V
Duration of Output Short Circuit ......................... Indefinite
Current Into Any Pin.................................................10mA
While Operating (Note 1) ..................................100µA
*Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above
those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional operation of
the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to Absolute
Maximum Rating Conditions for extended periods may affect device reliability.
+ 0.3V) to (V
DD
ELECTRICAL CHARACTERISTICS: V
*
Package Power Dissipation (TA ≤ 70°C)
8-Pin Plastic DIP.............................................730mW
SS
– 0.3V)
SS
14-Pin Plastic DIP...........................................800mW
Storage Temperature Range ................– 65°C to +150°C
Operating Temperature Range
C Device ................................................0°C to +70°C
I Device.............................................– 25°C to +85°C
Lead Temperature (Soldering, 10 sec) .................+300°C
= +5V, VSS = – 5V, TA = +25°C, unless otherwise indicated.
DD
Symbol Parameter Test Conditions Min Typ Max Unit
V
OS
TCV
OS
VOS/DT Offset Voltage vs Time — 150 — nV/mo
I
BIAS
I
BIAS
I
OS
R
IN
OL
V
OUT
CMVR Common-Mode – 4.3 — +3.5 V
MRR Common-Mode CMVR = – 4.3V to +3.5V 120 140 — dB
PSRR Power Supply ±3V to ±8V 120 140 — dB
e
N
I
N
GBW Unity-Gain Bandwidth — 0.4 — MHz
SR Slew Rate CL = 50 pF, RL = 10kW — 1 — V/µsec
VDD, V
SS
I
S
f
CH
NOTES: 1. Limiting input current to 100µA is recommended to avoid latch-up problems. Typically, 1mA is safe; however, this is not guaranteed.
Input Offset Voltage TA = +25°C—±2±5µV
0°C < TA < +70°C—±10 —
Average Temperature Coefficient of 0°C < TA < +70°C — 0.01 0.05 µV/°C
Input Offset Voltage
Input Bias Current TA = +25°C — 30 100 pA
(CLK On) 0°C < T
< +70°C — 100 —
A
– 25°C < TA < +85°C — 250 1000
Input Bias Current TA = +25°C — 15 30 pA
(CLK Off) 0°C < T
< +70°C—35—
A
– 25°C < TA < +85°C — 100 —
Input Offset Current — 25 150 pA
Input Resistance — 10
Large Signal Voltage Gain RL = 10kW, V
= ±4V 120 150 — dB
OUT
12
—W
Output Voltage Swing RL = 10kW ±4.7 ±4.85 — V
(Note 2) RL = 100kW — ±4.95 —
Voltage Range
Rejection Ratio
Rejection Ratio
Input Noise Voltage RS = 100W, DC to 1Hz — 0.2 1.5 µV
DC to 10Hz — 0.7 5 µV
P-P
P-P
Input Noise Current f = 10Hz — 0.01 — pA/√Hz
Overshoot — 15 — %
Operating Supply Range 5 — 16 V
Supply Current No Load — 1 3 mA
Internal Chopping Frequency Pins 12 – 14 Open (DIP) 100 275 — Hz
Clamp ON Current (Note 3) RL = 100kW 25 100 — µA
Clamp OFF Current (Note 3) – 4V ≤ V
2. Output clamp not connected. See typical characteristics curves for output swing versus clamp current characteristics.
< +10V — 1 — pA
OUT
3-282
TELCOM SEMICONDUCTOR, INC.
LOW NOISE, CHOPPER-ST ABILIZED
OPERATIONAL AMPLIFIER
1
TC7652
Capacitor Connection
Connect the null-storage capacitors to the CA and C
pins with a common connection to the C
TC7652) or to VSS (8-pin TC7652). When connecting to VSS,
avoid injecting load current IR drops into the capacitive
circuitry by making this connection directly via a separate
wire or PC trace.
pin (14-pin
RET
Output Clamp
In chopper-stabilized amplifiers, the output clamp pin
reduces overload recovery time. When a connection is
made to the inverting input pin (summing junction), a current
path is created between that point and the output pin, just
before the device output saturates. This prevents uncontrolled differential input voltages and charge buildup on
correction-storage capacitors. Output swing is reduced.
Clock
The TC7652 has a 550Hz internal oscillator, which is
divided by two before clocking the input chopper switches.
The 275Hz chopping frequency is available at INT CLK OUT
(pin 12) on 14-pin devices. In normal operation, INT/EXT
(pin 14), which has an internal pull-up, can be left open.
An external clock can also be used. To disable the
internal clock and use an external one, the INT/EXT pin must
be tied to VSS. The external clock signal is then applied to the
EXT CLK IN input (pin 13). An internal divide-by-two provides a 50% switching duty cycle. The capacitors are only
charged when EXT CLK IN is high, so a 50% to 80% positive
duty cycle is recommended for higher clock frequencies.
The external clock can swing between VDD and VSS, with the
logic threshold about 2.5V below VDD.
The output of the internal oscillator, before the divideby-two circuit, is available at EXT CLK IN when INT/EXT is
high or unconnected. This output can serve as the clock
input for a second TC7652 (operating in a master/slave
mode), so that both op amps will clock at the same frequency. This prevents clock intermodulation effects when
two TC7652's are used in a differential amplifier configuration.
TEST CIRCUIT
R
2
1 MΩ
R
1
1 kΩ
–
+
C
0.1 µF 0.1 µF
R
TC7652
C
OUTPUT
If the TC7652's output saturates, error voltages on the
external capacitors will slow overload recovery. This condi-
B
tion can be avoided if a strobe signal is available. The strobe
signal is applied to EXT CLK IN and the overload signal is
applied to the amplifier while the strobe is LOW. In this case,
neither capacitor will be charged. The low leakage of the
capacitor pins allow long measurements to be made with
negligible errors (typical capacitor drift is 10µV/sec).
APPLICATION NOTES
Component Selection
CA and CB (external capacitors) should be in the 0.1µF
to 1µF range. For minimum clock ripple noise, use a 1µF
capacitor in broad bandwidth circuits. For limited bandwidth
applications where clock ripple is filtered out, use a 0.1µF
capacitor for slightly lower offset voltage. High-quality filmtype capacitors (polyester or polypropylene) are recommended, although a lower grade (ceramic) may work in
some applications. For quickest settling after initial turn-on,
use low dielectric absorption capacitors (e.g., polypropylene). With ceramic capacitors, settling to 1µV takes
several seconds.
Static Protection
Although input diodes static-protect all device pins,
avoid strong electrostatic fields and discharges that can
cause degraded diode junction characteristics and produce
increased input-leakage currents.
Latch-Up
Junction-isolated CMOS circuits have a 4-layer (p-np-n) structure similar to an SCR. Sometimes this junction
can be triggered into a low-impedance state and produce
excessive supply current. Therefore, avoid applying voltage
greater than 0.3V beyond the supply rails to any pin. Establish the amplifier supplies at the same time or before any
input signals are applied. If this is not possible, drive circuits
must limit input current flow to under 1mA to avoid latch-up,
even under fault conditions.
Output Stage/Load Driving
The output circuit is high impedance (about 18kΩ). With
lesser loads, the chopper amplifier behaves somewhat like
a transconductance amplifier with an open-loop gain proportional to load resistance. (For example, the open-loop gain
is 17dB lower with a 1kΩ load than with a 10kΩ load.) If the
amp is used only for DC, the DC gain is typically greater than
120dB (even with a 1kΩ load), and this lower gain is
inconsequential. For wideband, the best frequency response
occurs with a load resistor of at least 10kΩ. This produces
2
3
4
5
6
7
8
TELCOM SEMICONDUCTOR, INC.
3-283
TC7652
CONNECTION OF INPUT GUARDS
LOW NOISE, CHOPPER-ST ABILIZED
OPERATIONAL AMPLIFIER
Inverting Amplifier
R
2
–
+
OUTPUT
TC7652 TC7652
INPUT
R
1
Noninverting Amplifier
R
1
INPUT
a 6dB/octave response from 0.1Hz to 2MHz, with phase
shifts of less than 2 degrees in the transition region, where
the main amplifier takes over from the null amplifier.
Thermoelectric Effects
The thermoelectric (Seebeck) effects in thermocouple
junctions of dissimilar metals, alloys, silicon, etc. limit ultrahigh-precision DC amplifiers. Unless all junctions are at the
same temperature, thermoelectric voltages around 0.1µV/
°C (up to tens of µV/°C for some materials) are generated.
To realize the low offset voltages of the chopper, avoid
temperature gradients. Enclose components to eliminate air
movement, especially from power-dissipating elements in
the system. Where possible, use low thermoelectric-coefficient connections. Keep power supply voltages and power
dissipation to a minimum. Use high-impedance loads and
seek maximum separation from surrounding heat-dissipating elements.
Guarding
To benefit from TC7652 low-input currents, take care
assembling printed circuit boards. Clean boards with alcohol or TCE, and blow dry with compressed air. To prevent
contamination, coat boards with epoxy or silicone rubber.
Even if boards are cleaned and coated, leakage currents may occur because input pins are next to pins at supply
potentials. To reduce this leakage, use guarding to lower the
Follower
–
INPUT
R
2
–
+
OUTPUT
TC7652
+
OUTPUT
voltage difference between the inputs and adjacent metal
runs. The guard (a conductive ring surrounding inputs) is
connected to a low-impedance point at about the same
voltage as inputs. The guard absorbs leakage currents from
high-voltage pins.
The 14-pin dual-in-line arrangement simplifies guarding. Like the LM108 pin configuration (but unlike the 101A
and 741), pins next to inputs are not used.
Pin Compatibility
Where possible, the 8-pin device pinout conforms to
such industry standards as the LM101 and LM741. Nullstoring external capacitors connect to pins 1 and 8, which
are usually for offset-null or compensation capacitors. 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 VDD by two capacitors from
those pins to VSS) provides compatibility. Replacing the
compensation capacitor between pins 1 and 8 by two
capacitors to VSS is required. The same operation (with the
removal of any connection to pin 5) works for LM101,
µA748, and similar 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.
3-284
TELCOM SEMICONDUCTOR, INC.
LOW NOISE, CHOPPER-ST ABILIZED
OPERATIONAL AMPLIFIER
1
TC7652
Some Applications
Figures 1 and 2 show basic inverting and noninverting
amplifier circuits using the output clamping circuit 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 (10kΩ load for
full swing). Overcome these limitations with a booster circuit
(Figure 3) 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, monitor loop gain stability.
INPUT
0.1 µF
+
–
CLAMP
R
3
0.1 µF
R
R
TC7652
OUTPUT
2
1
Figure 4 shows the clamp circuit of a zero-offset comparator. Because the clamp circuit requires the inverting
input to follow the input signal, problems with a chopperstabilized op amp are avoided. The threshold input must
tolerate the output clamp current ≈VIN/R without disrupting
other parts of the system.
Figure 5 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 6
shows an approximate connection.
V
0.1 µF
IN
+
–
200 kΩ
CLAMP
to 2 MΩ
0.1 µF
TC7652
V
OUT
V
TH
2
3
4
Figure 1. Noninverting Amplifier With Optional Clamp
R
2
R
1
INPUT
0.1 µF 0.1 µF
Figure 2. Inverting Amplifier With Optional Clamp Figure 5. 1437 Offset-Nulled by TC7652
–7.5V
+
IN
TC7652
–7.5V
0.1
µF
–
CLAMP
–
+
0.1
µF
+15V
+
–
–15V
10 kΩ
TC7652
OUTPUT
741
OUT
10 µF
Figure 4. Low Offset Comparator
+
–
IN
2
45
TC
7660
6
8
3
TC7652
Ω22 k
+
–
AMPLIFIER
10 µF
Ω1 M
FAST
Ω22 k
OUT
+15V
+7.5V
0V
5
6
7
Figure 3. Using 741 to Boost Output Drive Capability
TELCOM SEMICONDUCTOR, INC.
Figure 6. Splitting +15V With the 7660 at >95% Efficiency
8
3-285
TC7652
TYPICAL CHARACTERISTICS
Supply Current vs ± Supply Voltage
1400
1200
1000
800
600
400
SUPPLY CURRENT (µA)
200
0
2345678
± SUPPLY VOLTAGE (V)
1 mA
0.1 mA
0.01 mA
0.1 µA
0.01 µA
CLAMP CURRENT
0.1 nA
0.01 nA
Negative Clamp Current
1 µA
1 nA
1 pA
4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0
OUTPUT VOLTAGE (V)
Noise at 0.1 Hz to 1 Hz
1 µV/DIV
1 sec/DIV
VOLTAGE (µV)
INPUT OFFSET
Input Offset Voltage vs Common-Mode Voltage
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
–6
LOW NOISE, CHOPPER-ST ABILIZED
Output Resistance
vs Output Voltage
–5.0
SINK
–4.0
SOURCE
OUTPUT VOLTAGE (V)
–3.0
100
1 µV/DIV
0.5V/DIV
–4
COMMON-MODE VOLTAGE (V)
1k 10k 100k 1M
OUTPUT RESISTANCE (Ω)
Noise at 0.1 Hz to 100 Hz
1 sec/DIV
Slew Rate
5 µsec/DIV
–2 0 2 4
OPERATIONAL AMPLIFIER
1 mA
0.1 mA
0.01 mA
0.1 µA
0.01 µA
CLAMP CURRENT
0.1 nA
0.01 nA
1 pA
Positive Clamp Current
1 µA
1 nA
4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0
OUTPUT VOLTAGE (V)
Noise at 0.1 Hz to 10 Hz
2 µV/DIV
1 sec/DIV
Phase-Gain (Bode Plot)*
GAIN
60
50
PHASE
40
30
20
GAIN (dB)
10
0
–10
–20
1 10 100 1k 10k 100k 1M
*NOTE:
FREQUENCY (Hz)
±5V, ±2.5V supplies; no load to 10k load.
+240
+180
+120
+60
0
–60
–120
–180
PHASE (deg)
3-286
TELCOM SEMICONDUCTOR, INC.
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