Download 3V/5V Low-Power, Low-Noise, CMOS, Rail-to-Rail I/O Op Amps MAX9636/MAX9637/MAX9638 General Description Features

19-5228; Rev 2; 1/11
TION KIT
EVALUA BLE
IL
AVA A
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
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 temperature 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.
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
PART
TEMP RANGE
PIN-PACKAGE
MAX9636AXT+
-40NC to +125NC
6 SC70
MAX9637AXA+
-40NC to +125NC
8 SC70
MAX9638AVB+
-40NC to +125NC
10 UTQFN
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Applications
Portable Medical Instruments
Piezoelectric Transducer Amplifiers
Smoke Detectors
Battery-Powered Devices
General-Purpose Signal Conditioning
Notebooks
Portable Media Players
________________________________________________________________ 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.
MAX9636/MAX9637/MAX9638
General Description
MAX9636/MAX9637/MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
ABSOLUTE MAXIMUM RATINGS
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
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
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.
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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
VDD +
0.1
V
DC CHARACTERISTICS
Input Voltage Range
VIN+, VIN-
Input Offset Voltage
VOS
Input Offset Voltage Drift
(Note 3)
TCVOS
Guaranteed by CMRR
VSS 0.1
TA = +25NC
0.01
TA = -40NC to +125NC
3.5
MAX9636 only
7
MAX9637, MAX9638 only
10
TA = +25NC
Input Bias Current (Note 3)
IB
±0.1
TA = -40NC to +85NC
CMRR
VSS < VCM <
(VDD - 1.4V)
68
dB
104
124
100
120
Output Voltage Low
VOL
VOUT
Output Voltage High
VOH
VDD - VOUT
2
TA = -40NC to +125NC
VOUT = 0.4V from rails, RL = 600I
ISC
Short to VDD
55
Short to VSS
40
dB
mA
RL = 10kI
0.014
0.03
RL = 600I
RL = 10kI
0.044
0.08
0.019
0.04
RL = 600I
0.057
0.1
0.01
1
SHDN = VSS, VOUT = 0V to VDD (MAX9636,
MAX9638 only)
pA
86
77
Output Short-Circuit Current
Output Leakage in Shutdown
72
58
AOL
FV/NC
±800
TA = +25NC
(VSS - 0.1V) < VCM < (VDD + 0.1V)
VOUT = 0.25V from rails
Open-Loop Gain
mV
±0.8
±50
TA = -40NC to +125NC
Common-Mode Rejection Ratio
2.2
V
V
FA
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
(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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
AC CHARACTERISTICS
Input Voltage Noise Density
eN
Input Voltage Noise
Input Current Noise Density
Input Capacitance
Gain Bandwidth
Slew Rate
Capacitive Loading
Distortion
IN
f = 1kHz
38
0.1Hz ≤ f ≤ 10Hz
5
FVP-P
0.9
fA/√Hz
f = 1kHz
nV/√Hz
CIN
2
pF
GBW
1.5
MHz
SR
CLOAD
THD
Settling Time
0.9
V/Fs
No sustained oscillations
300
pF
f = 10kHz, VO = 2VP-P, AV = 1V/V
-68
f = 10kHz, VO = 2VP-P, AV = 1V/V,
VDD = 5.5V
-74
To 0.1%, VOUT = 2V step, AV = 1V/V
f = 1kHz (MAX9637, MAX9638)
Crosstalk
dB
11.5
Fs
100
f = 10kHz (MAX9637, MAX9638)
dB
80
POWER-SUPPLY CHARACTERISTICS
Power-Supply Range
Power-Supply Rejection Ratio
Quiescent Current
Shutdown Supply Current
VDD
PSRR
IDD
Guaranteed by PSRR
VIN+ = VIN- = VSS,
VDD - VSS = 2.1V
to 5.5V
Per amplifier
2.1
TA = +25NC
72
TA = -40NC to +125NC
69
TA = +25NC
5.5
100
36
TA = -40NC to +125NC
V
dB
55
60
FA
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)
Shutdown Input Bias Current
(Note 3)
Turn-On Time
ISHDN
tON
1.4
V
MAX9636, MAX9638 only
1
VSHDN = 0V to 3V (MAX9636, MAX9638
only)
60
Power-Up Time
tUP
VDD = 0V to 3.3V
18
Note 2: All devices are 100% production tested at TA = +25NC. Temperature limits are guaranteed by design.
Note 3: Parameter is guaranteed by design.
100
nA
Fs
Fs
3
MAX9636/MAX9637/MAX9638
ELECTRICAL CHARACTERISTICS (continued)
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 THERMAL
COEFFICIENT HYSTOGRAM
12
10
8
6
35
4
20
15
10
0
0
TA = +25°C
150
100
TA = +85°C
50
TA = +125°C
0
COMMON-MODE VOLTAGE (V)
INPUT OFFSET VOLTAGE
vs. SUPPLY VOLTAGE VCM = VDD/2
INPUT BIAS CURRENT
vs. COMMON-MODE VOLTAGE
OUTPUT VOLTAGE LOW vs. SINK CURRENT
VDD = 2.1V
TA = +85°C
-200
-600
1
2
3
4
5
6
0
OUTPUT VOLTAGE LOW vs. SINK CURRENT
VDD = 3.3V
OUTPUT VOLTAGE LOW vs. SINK CURRENT
VDD = 5V
TA = +85°C
150
TA = +25°C
100
TA = 0°C
50
350
TA = +125°C
300
OUTPUT VOLTAGE LOW (mV)
MAX9636 toc07
200
250
200
TA = +25°C
150
100
TA = 0°C
2
4
6
8
SINK CURRENT (mA)
10
12
200
TA = +25°C
150
100
TA = 0°C
TA = -40°C
2
0
4
6
5
10
15
SINK CURRENT (mA)
20
10
12
OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VDD = 2.1V, VOH = VDD - VOUT
1200
1000
TA = +125°C
800
TA = +85°C
600
400
TA = +25°C
TA = 0°C
TA = -40°C
0
0
8
200
TA = -40°C
0
0
250
SINK CURRENT (mA)
TA = +85°C
50
TA = -40°C
300
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
COMMON-MODE VOLTAGE (V)
TA = +125°C
TA = +85°C
350
0
-0.5
SUPPLY VOLTAGE (V)
250
400
50
OUTPUT VOLTAGE HIGH (mV)
200
TA = +125°C
450
TA = +125°C
MAX9636 toc06
MAX9636 toc05
0
500
-400
TA = +125°C
220
TA = +25°C
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
MAX9636 toc09
TA = +85°C
200
0
-0.5
OUTPUT VOLTAGE LOW (mV)
TA = +25°C
280
240
400
INPUT BIAS CURRENT (pA)
TA = 0°C
260
600
MAX9636 toc04
340
0
TA = 0°C
200
OFFSET VOLTAGE THERMAL COEFFICIENT (µV/°C)
360
0
250
OFFSET VOLTAGE (mV)
TA = -40°C
300
300
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
380
320
350
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
400
OFFSET VOLTAGE (µV)
25
TA = -40°C
400
5
2
4
30
450
OFFSET VOLTAGE (µV)
14
500
MAX9636 toc02
16
40
MAX9636 toc08
PERCENT OCCURANCE (%)
18
PERCENT OCCURANCE (%)
MAX9636 toc01
20
INPUT OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9636 toc03
OFFSET VOLTAGE HISTOGRAM
OUTPUT VOLTAGE LOW (mV)
MAX9636/MAX9637/MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
25
0
1
2
3
4
5
6
7
SOURCE CURRENT (mA)
8
9
10
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
TA = +125°C
1200
1000
TA = +85°C
800
600
TA = +25°C
400
5
10
15
20
25
MAX9636 toc11
400
37
35
33
TA = +25°C
31
TA = 0°C
29
TA = -40°C
TA = -40°C
27
PER AMPLIFIER
25
0
35
5
10 15 20 25 30 35 40 45 50
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
OPEN-LOOP GAIN AND PHASE
vs. FREQUENCY
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
DC COMMON-MODE REJECTION RATIO
vs. TEMPERATURE
60
45
40
0
20
-45
PHASE
0
1
10
100
-40
-50
-60
-70
-135
-80
-180
1000 10,000
-90
-40
0.1
-30
-90
-20
-60
0.001 0.01
-20
90
0.01
0.1
1
10
100
FREQUENCY (kHz)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
DC POWER-SUPPLY REJECTION RATIO
vs. TEMPERATURE
90
80
70
60
50
40
30
20
10
100
0.1
1
10
100
FREQUENCY (kHz)
1000 10,000
94
92
90
88
86
84
82
-50
-25
0
25
50
75
100
125
INPUT VOLTAGE NOISE vs. FREQUENCY
98
96
94
92
90
88
86
84
300
250
200
150
100
50
82
0
80
0
96
TEMPERATURE (°C)
MAX9636 toc17
MAX9636 toc16
100
98
80
1000 10,000
FREQUENCY (kHz)
MAX9636 toc15
-10
MAX9636 toc18
135
100
DC COMMON-MODE REJECTION RATIO (dB)
GAIN
80
0
CMRR (dB)
100
180
INPUT VOLTAGE NOISE (nV/√Hz)
120
MAX9636 toc14
SOURCE CURRENT (mA)
MAX9636 toc13
0.01
39
SOURCE CURRENT (mA)
140
OPEN-LOOP GAIN (dB)
TA = +25°C
TA = +85°C
41
0
30
DC POWER-SUPPLY REJECTION RATIO (dB)
0
600
TA = +125°C
43
TA = 0°C
TA = -40°C
0
TA = +85°C
800
200
TA = 0°C
200
TA = +125°C
1000
SUPPLY CURRENT vs. SUPPLY VOLTAGE
45
SUPPLY CURRENT (µA)
1400
OUTPUT VOLTAGE HIGH (mV)
1600
PHASE (DEG)
OUTPUT VOLTAGE HIGH (mV)
1800
POWER-SUPPLY REJECTION RATIO (dB)
1200
MAX9636 toc10
2000
OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VDD = 5V, VOH = VDD - VOUT
MAX9636 toc12
OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VDD = 3.3V, VOH = VDD - VOUT
-50
-25
0
25
50
75
TEMPERATURE (°C)
100
125
0.01
0.1
1
10
100
FREQUENCY (kHz)
5
MAX9636/MAX9637/MAX9638
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.)
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.)
0.1Hz TO 10Hz VOLTAGE vs. TIME
INPUT CURRENT NOISE vs. FREQUENCY
9
INPUT CURRENT NOISE (fA/√Hz)
MAX9636 toc20
MAX9636 toc19
10
8
5µVP-P NOISE
7
6
2µV/div
5
4
3
2
1
0
1
0.1
10
100
10s/div
1000
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION vs.
FREQUENCY VDD = 5.5V, AO = 1V/V,
VOUT = 2VP-P, RL = 10kI to VDD/2
TOTAL HARMONIC DISTORTION vs.
INPUT VOLTAGE AMPLITUDE
VDD = 5.5V, AO = 1V/V
-20
-30
-40
-50
-60
-70
-80
0
MAX9636 toc22
-10
TOTAL HARMONIC DISTORTION (dB)
MAX9636 toc21
0
TOTAL HARMONIC DISTORTION (dB)
MAX9636/MAX9637/MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
-20
-40
-60
-80
-100
-120
-90
0
1
2
3
4
5
0.01
6
0.1
1
100
FREQUENCY (kHz)
SMALL-SIGNAL TRANSIENT RESPONSE
LARGE-SIGNAL TRANSIENT RESPONSE
MAX9636 toc24
MAX9636 toc23
VIN
2V/div
VIN
100mV/div
VOUT
20mV/div
VOUT
500mV/div
1µs/div
6
10
INPUT VOLTAGE AMPLITUDE (VP-P)
2µs/div
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
STABILITY vs. CAPACITIVE AND RESISTIVE
LOAD RISO IN SERIES WITH CLOAD
PERCENT OVERSHOOT vs. RESISTIVE LOAD
20
15
10
CLOAD = 50pF
5
90
80
70
60
50
STABLE
40
30
20
0
UNSTABLE
10
-5
0
10
100
1000
10,000 100,000 1,000,000
100
1000
10,000
RESISTIVE LOAD (I)
CAPACITIVE LOAD (pF)
STABILITY vs. CAPACITIVE AND RESISTIVE LOAD
RP IN PARALLEL WITH CL
POWER-UP TIME
90
80
VDD
2V/div
70
60
STABLE
100,000
MAX9636 toc28
MAX9636 toc27
100
RESISTIVE LOAD (kI)
MAX9636 toc26
CLOAD = 100pF
CLOAD = 300pF
RESISTIVE LOAD (I)
PERCENT OVERSHOOT (%)
25
100
MAX9636 toc25
30
UNSTABLE
50
40
VOUT
500mV/div
30
20
10
0
100
1000
10,000
40µs/div
CAPACITIVE LOAD (pF)
TURN-ON TIME
MAX9636 toc29
SHDN
2V/div
VOUT
500mV/div
100µs/div
7
MAX9636/MAX9637/MAX9638
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.)
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
MAX9636/MAX9637/MAX9638
Pin Configurations
TOP VIEW
IN+ 1
+
MAX9636
VSS 2
IN- 3
6
VDD
5
SHDN
OUTA
1
INAINA+
8
VDD
2
7
OUTB
3
6
INB-
5
INB+
VSS 4
OUT
4
+
MAX9637
SC70
SC70
SHDNB SHDNA
7
OUTA
8
INA-
9
OUTB
10
6
MAX9638
+
1
2
VDD
INB+
5
VSS
4
INA+
3
INB-
UTQFN
Pin Description
PIN
8
MAX9636
(6 SC70)
MAX9637
(8 SC70)
MAX9638
(10 UTQFN)
NAME
FUNCTION
1
—
—
IN+
—
3
4
INA+
Positive Input
Positive Input A
—
5
2
INB+
Positive Input B
2
4
5
VSS
Negative Power Supply. Bypass with a 0.1FF capacitor to ground.
Negative Input
3
—
—
IN-
—
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
—
—
6
8
1
SHDN
VDD
Active-Low Shutdown
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
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 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 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 shutdown mode that greatly reduces quiescent current while
the device is not operational. This makes the device suitable for portable applications where power consumption
must be minimized.
Rail-to-Rail Input Stage
The operational amplifiers have parallel-connected nand 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 common-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 voltage 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 impedance 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).
9
MAX9636/MAX9637/MAX9638
Detailed Description
MAX9636/MAX9637/MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
High-Impedance
Sensor Front-Ends
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 capacitive loads. However, if the load also has a resistive
component then a voltage-divider is created, introducing 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 alternative 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 output swing proportionally.
The ICs interface to both current-output sensors, such
as photodiodes (Figure 3), and high-impedance voltage
sources, such as piezoelectric sensors. For currentoutput 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 introduced 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 impedance of the sensor output, a low input bias current with
minimal temperature variation is very important for these
applications.
MAX9636/
MAX9637/
MAX9638
+
-
RISO
RL
MAX9636/
MAX9637/
MAX9638
CL
VDD
PHOTODIODE
IN-
MAX9636
IN+
REF
Figure 3. The MAX9636 in a Sensor Preamp Configuration
RL
CL
Figure 2. Using a Parallel Resistor to Degenerate the Effect of
the Capacitive Load and Increase Stability
Figure 1. Using a Series Resistor to Isolate the Capacitive
Load from the Op Amp
10
RP
+
RL
AV =
≈ 1V/V
RL + RISO
OUT
SIGNAL
CONDITIONING/
FILTERS
MAX1286
ADC
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
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 connected 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 impedance 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 thresholds 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 output leakage current in this state to 0.01µA when the output is between 0V to VDD.
ADC Driver
The MAX9636/MAX9637/MAX9638 are low-power amplifiers ideal for driving high to medium-resolution ADCs.
Figure 3 shows how the MAX9636 is connected to a photodiode, 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
1
ADC
3V, 10 BIT
3V, 12 BIT
5V, 10 BIT
5V, 12 BIT
MAX9636
MAX1089
MAX1289
MAX1088
MAX1288
2
MAX9637
MAX1087
MAX1287
MAX1086
MAX1286
2
MAX9638
MAX1087
MAX1287
MAX1086
MAX1286
11
MAX9636/MAX9637/MAX9638
For best performance, follow standard high-impedance
layout techniques, which include the following:
MAX9636/MAX9637/MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
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
12
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
13
MAX9636/MAX9637/MAX9638
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.
MAX9636/MAX9637/MAX9638
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
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.
14
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
15
MAX9636/MAX9637/MAX9638
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.
MAX9636/MAX9637/MAX9738
3V/5V Low-Power, Low-Noise, CMOS,
Rail-to-Rail I/O Op Amps
Revision History
REVISION
NUMBER
REVISION
DATE
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
2
1/11
Corrected the MAX9637 pin configuration
DESCRIPTION
PAGES
CHANGED
—
1, 2, 3, 5, 6
8
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Maxim reserves the right to change the circuitry and specifications without notice at any time.
16
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