COS77SR

COS77
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Features

■ Low Offset Voltage: 50µV (Max.)
■ Low Drift: 0.2µV/ºC
■ Gain Bandwidth Product: 2MHz
■ Wide Supply Range ：±2.25V ~ ±18V
■ Low Quiescent Current: 1mA
■ Slew Rate: 1.2V/µs
■ Unity Gain Stable ■ Input Over-Voltage Protection ■ Extended Temperature Ranges
From -40°C to +125°C
■ Available in SOP-8/MSOP-8/DIP-8

Applications

■ Sensors and Controls
Thermocouples
Resistor thermal detectors (RTDs)
Strain bridges Shunt current measurements ■ Precision Filters ■ Data Acquisition
■ Medical Instrumentation
■ Optical Network Control Circuits ■ Wireless Base Station Control Circuits

General Description

The COS77 is a low power, precision
operational amplifier operated on ±2.25V to ±18V supplies. It has very low input offset voltage (50μV) maximum that is obtained by
trimming at the wafer stage. These low offset
voltages generally eliminate any need for external nulling. COS77 also features low input bias current and high open-loop gain. The low offset and high open-loop gain make COS77
particularly useful for high gain instrumentation
applications. The wide input voltage range of ±13 V
minimum combined with a high CMRR of
110dB and high input impedance provide high accuracy in the noninverting circuit config- uration. Excellent linearity and gain accuracy can be maintained even at high closed-loop
gains. The accuracy and stability of the COS77,
combined with the freedom from external nulling have made the COS77 an ideal choice for instrumentation applications.

Rev1.0
Copyright@2018 Cosine Nanoelectronics Inc. All rights reserved
The information provided here is believed to be accurate and re liable. Cosine Nanoelectronics assumes
no reliability for inaccuracies and omissions. Specifications d escribed and contained here are subjected
to change without notice on the purpose of improving the design and performance. All of this information
described herein should not be implied or granted for any third party.

36V, 2MHz, Precision

Low-Noise Operational Amplifiers
COS77
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1. Pin Configuration and Functions

Pin Functions
Name Description Note
+Vs Positive power supply A bypass capacitor of 0.1μF as close to the part as
possible should be placed between power supply pins or between supply pins and ground.
-Vs Negative power supply
or ground If it is not connected to ground, bypass it with a
capacitor of 0.1μF as close to the part as possible.
-IN Negative input Inverting input of the amplifier. Voltage range of this
pin can go from -Vs to +Vs
+IN Positive input Non-inverting input of the amplifier. This pin has the
same voltage range as -IN.
OUT Output The output voltage range extends to within millivolts
of each supply rail.
TRIM V OS Trim Optional, place a offset nulling resistor (e.g. 20kΩ)
between pin 1 & 8
NC No connection

2. Package and Ordering Information

Model Channel Order Number Package Package Option Marking
Information
COS77 1 COS77SR SOP-8 Tape and Reel, 3000 COS77SR
COS77MR MSOP-8 Tape and Reel, 3000 COS77MR
COS77DR DIP-8 Tape and Reel, 1500 COS77DR
COS77DT DIP-8 Tube, 50 COS77DT

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3. Product Specification
3.1 Absolute Maximum Ratings (1)

Parameter Rating Units
Power Supply: +Vs to -Vs 36 V
Differential Input Voltage Range ±0.5 V
Common Mode Input voltage Range(2) -Vs to +Vs V
Output Current 50 mA
Storage Temperature Range -65 to 150 °C
Junction Temperature 150 °C
Operating Temperature Range -40 to 125 °C
ESD Susceptibility, HBM 2000 V

(1) Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable
above the recommended operating conditions and stressing the pa rts to these levels is not recommended. In addition,
extended exposure to stresses above the recommended operating c onditions may affect device reliability. The absolute
maximum ratings are stress ratings only.
(2) Input terminals are diode-clamped to the power-supply rails . Input signals that can swing more than 0.5V beyond the
supply rails should be current-limited to 10mA or less.

3.2 Thermal Data
Parameter Rating Unit
Package Thermal Resistance 206 (MSOP8)
155 (SOP8)
125 (DIP8) °C/W

3.3 Recommended Operating Conditions
Parameter Rating Unit
DC Supply Voltage ±2.25V ~ ±18V V
Input common-mode voltage range -Vs+2 ~ +Vs-2 V
Operating ambient temper ature -40 to +85 °C

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3.4 Electrical Characteristics
(+V S=+15V, -V S=-15V, T A=+25°C, R L=10kΩ to V S/2, unless otherwise noted)
Parameter Symbol Conditions Min Typ Max Unit
Input Characteristics
Input Offset Voltage VOS ±15 ±50 μV
Input Offset Voltage Drift ΔVOS/ΔT -40 to 125°C 0.2 0.7 μV/°C
Input Bias Current IB ±1 ±6 nA
Input Offset Current IOS ± 1 ± 6 n A
Common-Mode Voltage Range VCM ± 1 3 ±14 V
Common-Mode Rejection Ratio CMRR 80 110 dB
Open-Loop Voltage Gain AOL R L ≥ 2kΩ, V O = ±10V 90 120 dB
Output Characteristics
Output Voltage Swing V O(PP) R L ≥ 10kΩ ±12 ±13.8 V
Short-Circuit Current I SC ±28 m A
Power Supply
Operating Voltage Range ±2.25 ±18 V
Power Supply Rejection Ratio PSRR 100 120 dB
Quiescent Current / Amplifier I Q 1.0 1.8 mA
Dynamic Performance
Gain Bandwidth Product GBWP C L=100pF, R L=10kΩ 2.0 MHz
Slew Rate SR CL=100pF, R L=10kΩ,
Av=1 1 . 2 V / μ s
Noise Performance
Voltage Noise Density e n f=1kHz 6.0 nV/√Hz

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4.0 Application Notes

Driving Capacitive Loads

Driving large capacitive loads can cause stability problems for voltage feedback op amps. As the
load capacitance increases, the feedback loop’s phase margin de creases, and the closed loop
bandwidth is reduced. This produces gain peaking in the frequen cy response, with overshoot and
ringing in the step response. A unity gain buffer (G = +1) is t he most sensitive to capacitive loads, but
all gains show the same general behavior.

When driving large capacitive loads with these op amps (e.g., > 100 pF when G = +1), a small series
resistor at the output (R ISO in Figure 1) improves the feedback loop’s phase margin (stabil ity) by
making the output load resistive at higher frequencies. It does not, however, improve the bandwidth.

To select R ISO, check the frequency response peaking (or step response oversh oot) on the bench. If
the response is reasonable, you do not need R ISO. Otherwise, start R ISO at 1 kΩ and modify its value
until the response is reasonable.
RISO
CLVOUT
VIN

Figure 1. Indirectly Driving Heavy Capacitive Load

An improvement circuit is shown in Figure 2. It provides DC acc uracy as well as AC stability. R F
provides the DC accuracy by connecting the inverting signal wit h the output, C F and R ISO serve to
counteract the loss of phase margin by feeding the high frequen cy component of the output signal
back to the amplifier’s inverting input, thereby preserving pha se margin in the overall feedback loop.

Figure 2. Indirectly Driving Heavy Capacitive Load with DC Accu racy
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For noninverting configuration, there are two others ways to in crease the phase margin: (a) by
increasing the amplifier’s gain or (b) by placing a capacitor i n parallel with the feedback resistor to
counteract the parasitic capacitance associated with inverting node, as shown in Figure 3.

Figure 3. Adding a Feedback Capacitor in the Noninverting Confi guration

Power-Supply Bypassing and Layout

The COS77 operates from a single +4.5V to +36V supply or dual ± 2.25V to ±18V supplies. For
single-supply operation, bypass the power supply +Vs with a 0.1 μF ceramic capacitor which should
be placed close to the +Vs pin. For dual-supply operation, both the +Vs and the -Vs supplies should
be bypassed to ground with separate 0.1μF ceramic capacitors. 2 .2μF tantalum capacitor can be
added for better performance.

The length of the current path is directly proportional to the magnitude of parasitic inductances and
thus the high frequency impedance of the path. High speed curre nts in an inductive ground return
create an unwanted voltage noise. Broad ground plane areas will reduce the parasitic inductance.
Thus a ground plane layer is important for high speed circuit d esign.

Typical Application Circuits

Differential Amplifier
The circuit shown in Figure 4 performs the differential functio n. If the resistors ratios are equal (R 4 /
R3 = R 2 / R 1), then V OUT = (V IP – V IN) × R 2 / R 1 + V REF.

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VOUTVINR2
VIP
R3R1
R4
VREF

Figure 4. Differential Amplifier

Low Pass Active Filter
When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is
often required. The simplest way to establish this limited band width is to place an RC filter at the
noninverting terminal of the amplifier. If even more attenuatio n is needed, a multiple pole filter is
required. The Sallen-Key filter can be used for this task, as F igure 5. For best results, the amplifier
should have a bandwidth that is 8 to 10 times the filter freque ncy bandwidth. Failure to follow this
guideline can result in reduction of phase margin. The large va lues of feedback resistors can couple
with parasitic capacitance and cause undesired effects such as ringing or oscillation in high-speed
amplifiers. Keep resistors value as low as possible and consist ent with output loading consideration.

Figure 5. Two-Pole Low-Pass Sallen-Key Active Filter
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5. Package Information

5.1 SOP8 (Package Outline Dimensions)

5.2 MSOP8 (Package Outline Dimensions)

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5.3 DIP8 (Package Outline Dimensions)

6. Related Parts

Part Number Description
COS6041/2/4 24kHz, 0.5μA, RRIO Op Amps, 1.8 to 5.5V Supply
COS1347/2347/4347 350kHz, 15μA, RRIO Op Amps, 1.8 to 5.5V Suppl y
COS6001/2/4 1.5MHz, 50μA, RRIO Op Amps, 1.8 to 5.5V Supply
COS1314/2314/4314 3MHz, 150μA, RRIO Op Amps, 1.8 to 5.5V Supply
COS821/2/4 5MHz, 300μA, RRIO Op Amps, 1.8 to 5.5V Supply
COS1374/2374/4374 7MHz, 500μA, RRIO Op Amps, 1.8 to 5.5V Supply
COS721/2/4 10MHz, 650μA, RRIO Op Amps, 2.1 to 5.5V Supply
COS1333/2333/4333 0.5MHz, 18μA, RRIO Op Amps, 1.8 to 5.5V Suppl y, Zero Drift, Vos<10μV COS8551/2/4 1.5MHz, 55μA, RRIO Op Amps, 1.8 to 5.5V Supply, Zer o Drift, Vos<10μV