_______________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
19-5228; Rev 2; 1/11
General Description
The MAX9636/MAX9637/MAX9638 are single-supply,
CMOS input op amps featuring wide bandwidth at low
quiescent current, making them suitable for a broad
range of battery-powered applications such as portable
medical instruments, portable media players, and smoke
detectors. A combination of extremely low input bias
currents, low input current noise and low input voltage
noise allows interface to high-impedance sources such
as photodiode and piezoelectric sensors. These devices
are also ideal for general-purpose signal processing
functions such as filtering and amplification in a broad
range of portable, battery-powered applications.
The ICs feature a maximized ratio of gain bandwidth
(GBW) to supply current. The devices operate from a
single 2.1V to 5.5V supply at a typical quiescent supply
current of 36µA. For additional power conservation, the
MAX9636 and MAX9638 offer a low-power shutdown
mode that reduces supply current to 1µA and places the
amplifiers’ outputs into a high-impedance state.
The ICs are specified over the automotive operating tem-
perature range (-40°C to +125°C). The single is offered
in a space-saving, 6-pin SC70 package, while the dual is
offered in tiny, 8-pin SC70 and 10-pin UTQFN packages.
Applications
Portable Medical Instruments
Piezoelectric Transducer Amplifiers
Smoke Detectors
Battery-Powered Devices
General-Purpose Signal Conditioning
Notebooks
Portable Media Players
Features
S Low Input Voltage-Noise Density: 38nV/√Hz
S Low Input Current-Noise Density: 0.9fA/√Hz
S Ultra-Low 0.1pA Bias Current
S Low 36µA Quiescent Current
S 1µA Quiescent Current in Shutdown
S Wide 1.5MHz Bandwidth
S Single-Supply Operation VDD = 2.1V to 5.5V
S Available in Tiny 6-Pin SC70, 8-Pin SC70, and
10-Pin UTQFN Packages
S -40°C to +125°C Operating Temperature Range
Ordering Information
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX9636AXT+ -40NC to +125NC 6 SC70
MAX9637AXA+ -40NC to +125NC 8 SC70
MAX9638AVB+ -40NC to +125NC 10 UTQFN
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
2
Stresses beyond 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 beyond 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.
VDD, SHDN to VSS ..................................................-0.3V to +6V
IN+, IN-, OUT ....................................GND - 0.3V to VDD + 0.3V
Continuous Input Current (any pins) ............................... Q20mA
Output Short Circuit to VDD or VSS Duration .......................... 5s
Thermal Limits (Note 1)
Multiple Layer PCB
Continuous Power Dissipation (TA = +70NC)
6-Pin SC70 (derate 3.1mW/°C above +70NC) ............245mW
BJA .......................................................................326.5°C/W
BJC .........................................................................115°C/W
8-Pin SC70 (derate 3.1mW/NC above +70NC) .............245mW
BJA .........................................................................326°C/W
BJC .........................................................................115NC/W
10-Pin UTQFN (derate 7mW/NC above +70NC) ........558.7mW
BJA ......................................................................143.2NC/W
BJC .........................................................................20.1NC/W
Operating Temperature Range ........................ -40NC to +125NC
Junction Temperature ....................................................+150NC
Lead Temperature (soldering 10s) .................................+300NC
Soldering Temperature (reflow) ......................................+260NC
ELECTRICAL CHARACTERISTICS
(VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VCM = VDD/2, RL = 10kI to VDD/2, SHDN = VDD, TA = -40NC to +125NC. Typical values are
at TA = +25NC, unless otherwise noted.) (Note 2)
ABSOLUTE MAXIMUM RATINGS
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DC CHARACTERISTICS
Input Voltage Range VIN+, VIN-Guaranteed by CMRR VSS -
0.1
VDD +
0.1 V
Input Offset Voltage VOS TA = +25NC 0.01 2.2 mV
TA = -40NC to +125NC 3.5
Input Offset Voltage Drift
(Note 3) TCVOS MAX9636 only 7 FV/NC
MAX9637, MAX9638 only 10
Input Bias Current (Note 3) IB
TA = +25NC ±0.1 ±0.8
pA
TA = -40NC to +85NC ±50
TA = -40NC to +125NC ±800
Common-Mode Rejection Ratio CMRR
VSS < VCM <
(VDD - 1.4V)
TA = +25NC 72 86
dB
TA = -40NC to +125NC 68
(VSS - 0.1V) < VCM < (VDD + 0.1V) 58 77
Open-Loop Gain AOL VOUT = 0.25V from rails 104 124 dB
VOUT = 0.4V from rails, RL = 600I100 120
Output Short-Circuit Current ISC Short to VDD 55 mA
Short to VSS 40
Output Voltage Low VOL VOUT RL = 10kI0.014 0.03 V
RL = 600I0.044 0.08
Output Voltage High VOH VDD - VOUT RL = 10kI0.019 0.04 V
RL = 600I0.057 0.1
Output Leakage in Shutdown SHDN = VSS, VOUT = 0V to VDD (MAX9636,
MAX9638 only) 0.01 1 FA
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
3
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VCM = VDD/2, RL = 10kI to VDD/2, SHDN = VDD, TA = -40NC to +125NC. Typical values are
at TA = +25NC, unless otherwise noted.) (Note 2)
Note 2: All devices are 100% production tested at TA = +25NC. Temperature limits are guaranteed by design.
Note 3: Parameter is guaranteed by design.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
AC CHARACTERISTICS
Input Voltage Noise Density eNf = 1kHz 38 nV/√Hz
Input Voltage Noise 0.1Hz ≤ f ≤ 10Hz 5 FVP-P
Input Current Noise Density INf = 1kHz 0.9 fA/√Hz
Input Capacitance CIN 2 pF
Gain Bandwidth GBW 1.5 MHz
Slew Rate SR 0.9 V/Fs
Capacitive Loading CLOAD No sustained oscillations 300 pF
Distortion THD
f = 10kHz, VO = 2VP-P, AV = 1V/V -68
dB
f = 10kHz, VO = 2VP-P, AV = 1V/V,
VDD = 5.5V -74
Settling Time To 0.1%, VOUT = 2V step, AV = 1V/V 11.5 Fs
Crosstalk f = 1kHz (MAX9637, MAX9638) 100 dB
f = 10kHz (MAX9637, MAX9638) 80
POWER-SUPPLY CHARACTERISTICS
Power-Supply Range VDD Guaranteed by PSRR 2.1 5.5 V
Power-Supply Rejection Ratio PSRR
VIN+ = VIN- = VSS,
VDD - VSS = 2.1V
to 5.5V
TA = +25NC 72 100
dB
TA = -40NC to +125NC 69
Quiescent Current IDD Per amplifier TA = +25NC 36 55 FA
TA = -40NC to +125NC 60
Shutdown Supply Current IDD_SHDN VSHDN P VIL (MAX9636, MAX9638 only) 1 FA
Shutdown Input VIL Over the power-supply range (MAX9636,
MAX9638 only) 0.5 V
Shutdown Input VIH Over the power-supply range (MAX9636,
MAX9638 only) 1.4 V
Shutdown Input Bias Current
(Note 3) ISHDN MAX9636, MAX9638 only 1 100 nA
Turn-On Time tON VSHDN = 0V to 3V (MAX9636, MAX9638
only) 60 Fs
Power-Up Time tUP VDD = 0V to 3.3V 18 Fs
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
4
Typical Operating Characteristics
(VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VCM = VDD/2, RL = 10kI to VDD/2, SHDN = VDD, TA = -40NC to +125NC. Typical values are at
TA = +25NC, unless otherwise noted.)
OFFSET VOLTAGE HISTOGRAM
MAX9636 toc01
OFFSET VOLTAGE (mV)
PERCENT OCCURANCE (%)
0.90.7 1.00.80.1 0.2 0.3 0.4 0.5 0.60
2
4
6
8
10
12
14
16
18
20
0
OFFSET VOLTAGE THERMAL
COEFFICIENT HYSTOGRAM
MAX9636 toc02
OFFSET VOLTAGE THERMAL COEFFICIENT (µV/°C)
PERCENT OCCURANCE (%)
1.00.1 0.2 0.3 0.5 0.70.6 0.80.4 0.9
5
10
15
20
25
30
35
40
0
0
INPUT OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9636 toc03
COMMON-MODE VOLTAGE (V)
OFFSET VOLTAGE (µV)
3.53.02.0 2.50.5 1.0 1.50
50
100
150
200
250
300
350
400
450
500
0
-0.5
4.0
TA = 0°C
TA = +25°C
TA = +85°C
TA = +125°C
TA = -40°C
INPUT OFFSET VOLTAGE
vs. SUPPLY VOLTAGE VCM = VDD/2
MAX9636 toc04
SUPPLY VOLTAGE (V)
OFFSET VOLTAGE (µV)
54321
220
240
260
280
300
320
340
360
380
400
200
0 6
TA = -40°C
TA = +85°C
TA = +125°C
TA = 0°C
TA = +25°C
INPUT BIAS CURRENT
vs. COMMON-MODE VOLTAGE
MAX9636 toc05
COMMON-MODE VOLTAGE (V)
INPUT BIAS CURRENT (pA)
3.53.02.52.01.51.00.50
-400
-200
0
200
400
600
-600
-0.5 4.0
TA = +125°C
TA = +85°C
TA = +25°C
OUTPUT VOLTAGE LOW vs. SINK CURRENT
VDD = 2.1V
MAX9636 toc06
SINK CURRENT (mA)
OUTPUT VOLTAGE LOW (mV)
108642
50
100
150
200
250
300
350
400
450
500
0
0 12
TA = +25°C
TA = 0°C
TA = -40°C
TA = +125°C
TA = +85°C
OUTPUT VOLTAGE LOW vs. SINK CURRENT
VDD = 3.3V
MAX9636 toc07
SINK CURRENT (mA)
OUTPUT VOLTAGE LOW (mV)
108642
50
100
150
200
250
0
0 12
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
TA = 0°C
OUTPUT VOLTAGE LOW vs. SINK CURRENT
VDD = 5V
MAX9636 toc08
SINK CURRENT (mA)
OUTPUT VOLTAGE LOW (mV)
2015105
50
100
150
200
250
300
350
0
0 25
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
TA = 0°C
OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VDD = 2.1V, VOH = VDD - VOUT
MAX9636 toc09
SOURCE CURRENT (mA)
OUTPUT VOLTAGE HIGH (mV)
987654321
200
400
600
800
1000
1200
0
0 10
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
TA = 0°C
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
5
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VCM = VDD/2, RL = 10kI to VDD/2, SHDN = VDD, TA = -40NC to +125NC. Typical values are at
TA = +25NC, unless otherwise noted.)
OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VDD = 3.3V, VOH = VDD - VOUT
MAX9636 toc10
SOURCE CURRENT (mA)
OUTPUT VOLTAGE HIGH (mV)
302515 20105
200
400
600
800
1000
1200
1400
1600
1800
2000
0
0 35
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
TA = 0°C
OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VDD = 5V, VOH = VDD - VOUT
MAX9636 toc11
SOURCE CURRENT (mA)
OUTPUT VOLTAGE HIGH (mV)
454035302520151050 50
200
400
600
800
1000
1200
0
TA = +125°C
TA = +85°C
TA = +25°C
TA = 0°C
TA = -40°C
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX9636 toc12
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
5.55.04.0 4.53.0 3.52.5
27
29
31
33
35
37
39
41
43
45
25
2.0 6.0
TA = +125°C
TA = +85°C
TA = +25°C
PER AMPLIFIER
TA = 0°C
TA = -40°C
OPEN-LOOP GAIN AND PHASE
vs. FREQUENCY
MAX9636 toc13
FREQUENCY (kHz)
1000
1001 100.10.01
0
OPEN-LOOP GAIN (dB)
-40
-20
20
40
60
80
100
120
140
-60
-135
PHASE (DEG)
-90
-45
0
45
90
135
180
0.001 10,000
-180
PHASE
GAIN
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9636 toc14
FREQUENCY (kHz)
CMRR (dB)
10001001010.1
-80
-70
-60
-50
-40
-30
-20
-10
0
-90
0.01 10,000
DC COMMON-MODE REJECTION RATIO
vs. TEMPERATURE
MAX9636 toc15
TEMPERATURE (°C)
DC COMMON-MODE REJECTION RATIO (dB)
1007525 500-25
82
84
86
88
90
92
94
96
98
100
80
-50 125
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9636 toc16
FREQUENCY (kHz)
POWER-SUPPLY REJECTION RATIO (dB)
10001001010.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10,000
DC POWER-SUPPLY REJECTION RATIO
vs. TEMPERATURE
MAX9636 toc17
TEMPERATURE (°C)
DC POWER-SUPPLY REJECTION RATIO (dB)
1007525 500-25
82
84
86
88
90
92
94
96
98
100
80
-50 125
INPUT VOLTAGE NOISE vs. FREQUENCY
MAX9636 toc18
FREQUENCY (kHz)
INPUT VOLTAGE NOISE (nV/√Hz)
1010.1
50
100
150
200
250
300
0
0.01 100
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
6
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VCM = VDD/2, RL = 10kI to VDD/2, SHDN = VDD, TA = -40NC to +125NC. Typical values are at
TA = +25NC, unless otherwise noted.)
INPUT CURRENT NOISE vs. FREQUENCY
MAX9636 toc19
FREQUENCY (Hz)
INPUT CURRENT NOISE (fA/√Hz)
100101
1
2
3
4
5
6
7
8
9
10
0
0.1 1000
0.1Hz TO 10Hz VOLTAGE vs. TIME
MAX9636 toc20
2µV/div
5µVP-P NOISE
10s/div
TOTAL HARMONIC DISTORTION vs.
INPUT VOLTAGE AMPLITUDE
VDD = 5.5V, AO = 1V/V
MAX9636 toc21
INPUT VOLTAGE AMPLITUDE (VP-P)
TOTAL HARMONIC DISTORTION (dB)
54321
-80
-70
-60
-50
-40
-30
-20
-10
0
-90
0 6
TOTAL HARMONIC DISTORTION vs.
FREQUENCY VDD = 5.5V, AO = 1V/V,
VOUT = 2VP-P, RL = 10kI to VDD/2
MAX9636 toc22
FREQUENCY (kHz)
TOTAL HARMONIC DISTORTION (dB)
1010.1
-100
-80
-60
-40
-20
0
-120
0.01 100
SMALL-SIGNAL TRANSIENT RESPONSE
MAX9636 toc23
1µs/div
VOUT
20mV/div
VIN
100mV/div
LARGE-SIGNAL TRANSIENT RESPONSE
MAX9636 toc24
VIN
2V/div
VOUT
500mV/div
2µs/div
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
7
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VCM = VDD/2, RL = 10kI to VDD/2, SHDN = VDD, TA = -40NC to +125NC. Typical values are at
TA = +25NC, unless otherwise noted.)
PERCENT OVERSHOOT vs. RESISTIVE LOAD
MAX9636 toc25
RESISTIVE LOAD (I)
PERCENT OVERSHOOT (%)
100,00010,0001000100
0
5
10
15
20
25
30
-5
10 1,000,000
CLOAD = 300pF
CLOAD = 50pF
CLOAD = 100pF
STABILITY vs. CAPACITIVE AND RESISTIVE
LOAD RISO IN SERIES WITH CLOAD
MAX9636 toc26
CAPACITIVE LOAD (pF)
RESISTIVE LOAD (I)
10,0001000
10
20
30
40
50
60
70
80
90
100
0
100 100,000
UNSTABLE
STABLE
STABILITY vs. CAPACITIVE AND RESISTIVE LOAD
RP IN PARALLEL WITH CL
MAX9636 toc27
CAPACITIVE LOAD (pF)
RESISTIVE LOAD (kI)
1000
10
20
30
40
50
60
70
80
90
100
0
100 10,000
UNSTABLE
STABLE
POWER-UP TIME
MAX9636 toc28
VDD
2V/div
40µs/div
VOUT
500mV/div
TURN-ON TIME
MAX9636 toc29
SHDN
2V/div
VOUT
500mV/div
100µs/div
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
8
Pin Configurations
Pin Description
VSS
OUT
IN-
1 6 VDD
5
IN+
SC70
TOP VIEW
2
3 4
INB-
INB+VSS
1
2
8
7
VDD
OUTBINA-
INA+
OUTA
SC70
+
+
+
3
4
6
5
MAX9636
MAX9637
SHDN
OUTA
INA-
OUTB
VSS
INA+
INB-
UTQFN
10
9
8
3
4
5
7
SHDNB
6
SHDNA
MAX9638
1 2
VDD INB+
PIN
NAME FUNCTION
MAX9636
(6 SC70)
MAX9637
(8 SC70)
MAX9638
(10 UTQFN)
1 — — IN+ Positive Input
— 3 4 INA+ Positive Input A
— 5 2 INB+ Positive Input B
2 4 5 VSS Negative Power Supply. Bypass with a 0.1FF capacitor to ground.
3 — — IN- Negative Input
— 2 9 INA- Negative Input A
— 6 3 INB- Negative Input B
4 — — OUT Output
— 1 8 OUTA Output A
— 7 10 OUTB Output B
— — 6 SHDNA Active-Low Shutdown A
— — 7 SHDNB Active-Low Shutdown B
5 — — SHDN Active-Low Shutdown
6 8 1 VDD Positive Power Supply. Bypass with a 0.1FF capacitor to ground.
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
9
Detailed Description
The MAX9636/MAX9637/MAX9638 are single-supply,
CMOS input op amps. They feature wide bandwidth at
low quiescent current, making them suitable for a broad
range of battery-powered applications such as por-
table medical instruments, portable media players, and
smoke detectors. A combination of extremely low input
bias currents, low input current noise, and low input volt-
age noise allows interface to high-impedance sources
such as photodiode and piezoelectric sensors. These
devices are also ideal for general-purpose signal pro-
cessing functions such as filtering and amplification in a
broad range of portable, battery-powered applications.
The devices’ operational common-mode range extends
0.1V beyond the supply rails, allowing for a wide variety
of single-supply applications.
The ICs also feature low quiescent current and a shut-
down mode that greatly reduces quiescent current while
the device is not operational. This makes the device suit-
able for portable applications where power consumption
must be minimized.
Rail-to-Rail Input Stage
The operational amplifiers have parallel-connected n-
and p-channel differential input stages that combine
to accept a common-mode range extending 100mV
beyond the supply rails. The n-channel stage is active
for common-mode input voltages typically greater than
(VDD - 1.2V), and the p-channel stage is active for com-
mon-mode input voltages typically less than (VDD - 1.4V).
A small transition region exists, typically VDD - 1.4 to VDD
- 1.2V, during which both pairs are on.
Rail-to-Rail Output Stage
The maximum output voltage swing is load dependent.
However, it is guaranteed to be within 100mV of the
positive rail even with 3mA of load current. To maximize
the output current sourcing capability, these parts do
not come with built-in short-circuit protection. If loads
heavier than 600ω must be driven, then ensure that the
maximum allowable power dissipation is not exceeded
(see the Absolute Maximum Ratings section).
Low Input Bias Current
This op-amp family features ultra-low 0.1pA (typ) input
bias current and guaranteed maximum current of Q50pA
over -40NC to +85NC when the input common-mode volt-
age is at midrail. For the -40NC to +85NC temperature
range, the variation in the input bias current is small
with changes in the input voltage due to very high input
impedance (in the order of 100GI).
Power-Up Time
The ICs typically require a power-up time of 18µs.
Supply settling time depends on the supply voltage,
the value of the bypass capacitor, the output imped-
ance of the incoming supply, and any lead resistance or
inductance between components. Op amp settling time
depends primarily on the output voltage and is slew-rate
limited. The output settles in approximately 11.5µs for
VDD = 3V and VOUT = VDD/2V (see the Power-Up Time
graph in the Typical Operating Characteristics section).
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
10
Driving Capacitive Loads
The ICs have a high tolerance for capacitive loads.
In unity-gain configuration, the op amps can typically
drive up to 300pF pure capacitive load. Increasing the
gain enhances the amplifier’s ability to drive greater
capacitive loads. In unity-gain configurations, capacitive
load drive can be improved by inserting a small (5I to
30I) isolation resistor, RISO, in series with the output,
as shown in Figure 1. This significantly reduces ringing
while maintaining DC performance for purely capaci-
tive loads. However, if the load also has a resistive
component then a voltage-divider is created, introduc-
ing a direct current (DC) error at the output. The error
introduced is proportional to the ratio RISO/RL, which
is usually negligible in most cases. Applications that
cannot tolerate this slight DC error can use an alterna-
tive approach of providing stability by placing a suitable
resistance in parallel with the capacitive load as shown
in Figure 2 (see the Typical Operating Characteristics
section for graphs of the stable operating region for
various capacitive loads vs. resistive loads). While this
approach of adding a resistor parallel to the load does
not introduce DC error, it nevertheless reduces the out-
put swing proportionally.
High-Impedance
Sensor Front-Ends
The ICs interface to both current-output sensors, such
as photodiodes (Figure 3), and high-impedance voltage
sources, such as piezoelectric sensors. For current-
output sensors, a transimpedance amplifier is the most
noise-efficient method for converting the input signal to
a voltage. High-value feedback resistors are commonly
chosen to create large gains, while feedback capacitors
help stabilize the amplifier by cancelling any poles intro-
duced in the feedback function by the highly capacitive
sensor or cabling. A combination of low-current noise
and low-voltage noise is important for these applications.
Take care to calibrate out photodiode dark current if DC
accuracy is important. The high bandwidth and slew
rate also allows AC signal processing in certain medical
photodiode sensor applications such as pulse oximetry.
For voltage-output sensors, a noninverting amplifier is
typically used to buffer and/or apply a small gain to the
input voltage signal. Due to the extremely high imped-
ance of the sensor output, a low input bias current with
minimal temperature variation is very important for these
applications.
Figure 3. The MAX9636 in a Sensor Preamp Configuration
Figure 1. Using a Series Resistor to Isolate the Capacitive
Load from the Op Amp
Figure 2. Using a Parallel Resistor to Degenerate the Effect of
the Capacitive Load and Increase Stability
SIGNAL
CONDITIONING/
FILTERS
PHOTODIODE
IN-
IN+
VDD
OUT
REF
ADC
MAX1286
MAX9636
-
+RL
RL
RL + RISO
AV =
RISO
≈ 1V/V
CL
MAX9636/
MAX9637/
MAX9638
-
+RPRLCL
MAX9636/
MAX9637/
MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
11
For best performance, follow standard high-impedance
layout techniques, which include the following:
U Using shielding techniques to guard against parasitic
leakage paths. For example, put a trace connected to
the noninverting input around the inverting input.
U Minimizing the amount of stray capacitance connect-
ed to op amp’s inputs to improve stability. To achieve
this, minimize trace lengths and resistor leads by
placing external components as close as possible to
the package.
U Use separate analog and digital power supplies.
Applications Information
Shutdown Operation
The MAX9636/MAX9638 feature an active-low shutdown
mode that sends the inputs and output into high imped-
ance and substantially lowers the quiescent current.
Active-Low Input
The shutdown active-low (VIL) and high (VIH) threshold
voltages are designed for ease of integration with digital
controls, such as microcontroller outputs. These thresh-
olds are independent of supply, eliminating the need for
external pulldown circuitry.
Output During Shutdown
The MAX9636/MAX9638 output is in a high-impedance
state while SHDN is low. The device structure limits the out-
put leakage current in this state to 0.01µA when the out-
put is between 0V to VDD.
ADC Driver
The MAX9636/MAX9637/MAX9638 are low-power ampli-
fiers ideal for driving high to medium-resolution ADCs.
Figure 3 shows how the MAX9636 is connected to a pho-
todiode, with the amplifier output connected to additional
signal conditioning/filtering, or directly to the ADC. The
MAX1286–MAX1289 family of low-power, 12-bit ADCs are
ideal for connecting to the MAX9636/MAX9637/MAX9638.
The MAX1286–MAX1289 ADCs offer sample rates up
to 150ksps, with 3V and 5V supplies, as well as 1- and
2-channel options. These ADCs dissipate just 15µA when
sampling at 10ksps and 0.2µA in shutdown. Offered in
tiny 8-pin SOT23 and 3mm x 3mm TDFN packages, the
MAX1286–MAX1289 ADCs are an ideal fit to pair with
the MAX9636/MAX9637/MAX9638 amplifiers in portable
applications.
Similarly, the MAX1086–MAX1089 is a family of 10-bit
pin-compatible low-power ADCs with the same 3V/5V,
1- and 2-channel options. Table 1 details the amplifier and
ADC pairings for single- and dual-channel applications.
Chip Information
PROCESS: BiCMOS
Table 1. Recommended Amplifiers/ADCs
CHANNELS AMPLIFIER ADC
3V, 10 BIT 3V, 12 BIT 5V, 10 BIT 5V, 12 BIT
1 MAX9636 MAX1089 MAX1289 MAX1088 MAX1288
2 MAX9637 MAX1087 MAX1287 MAX1086 MAX1286
2 MAX9638 MAX1087 MAX1287 MAX1086 MAX1286
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
12
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
6 SC70 X6SN+1 21-0077 90-0189
8 SC70 X8CN+1 21-0460 90-0348
10 UTQFN V101A1CN+1 21-0028 90-0287
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
13
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
14
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
15
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9738
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 6/10 Initial release —
1 9/10
Removed future product references, updated Input Offset Voltage Drift
conditions, updated Output Short-Circuit Current typ value, updated Input
Current Noise Density typ value, and added Crosstalk parameter to the
Electrical Characteristics table, modified TOCs 12, 14, 19
1, 2, 3, 5, 6
2 1/11 Corrected the MAX9637 pin configuration 8
