19-4398; Rev 1; 12/10
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
General Description
The MAX9945 operational amplifier features an excellent
combination of low operating power and low input volt-
age noise. In addition, MOS inputs enable the MAX9945
to feature low input bias currents and low input current
noise. The device accepts a wide supply voltage range
from 4.75V to 38V and draws a low 400µA quiescent cur-
rent. The MAX9945 is unity-gain stable and is capable of
rail-to-rail output voltage swing.
The MAX9945 is ideal for portable medical and industri-
al applications that require low noise analog front-ends
for performance applications such as photodiode trans-
impedance and chemical sensor interface circuits.
The MAX9945 is available in both an 8-pin µMAX
®
and
a space-saving, 6-pin TDFN package, and is specified
over the automotive operating temperature range
(-40°C to +125°C).
Features
o
+4.75V to +38V Single-Supply Voltage Range
o
±2.4V to ±19V Dual-Supply Voltage Range
o
Rail-to-Rail Output Voltage Swing
o
400µA Low Quiescent Current
o
50fA Low Input Bias Current
√
o
1fA/√
Hz
Low Input Current Noise
√
o
15nV/√
Hz
Low Noise
o
3MHz Unity-Gain Bandwidth
o
Wide Temperature Range from -40°C to +125°C
o
Available in Space-Saving, 6-Pin TDFN Package
(3mm x 3mm)
MAX9945
Applications
Medical Pulse Oximetry
Photodiode Sensor Interface
Industrial Sensors and Instrumentation
Chemical Sensor Interface
High-Performance Audio Line Out
Active Filters and Signal Processing
µMAX is a registered trademark of Maxim Integrated Products, Inc.
PART
MAX9945ATT+
MAX9945AUA+
Ordering Information
TEMP RANGE
PIN-
PACKAGE
TOP
MARK
AUE
—
-40°C to +125°C 6 TDFN-EP*
-40°C to +125°C 8 µMAX
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
Typical Operating Circuit
V
CC
PHOTODIODE
IN-
OUT
MAX9945
IN+
V
EE
SIGNAL
CONDITIONING/
FILTERS
ADC
________________________________________________________________
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.
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
MAX9945
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V
CC
to V
EE
) ..................................-0.3V to +40V
IN+, IN-, OUT Voltage......................(V
EE
- 0.3V) to (V
CC
+ 0.3V)
IN+ to IN- .............................................................................±12V
OUT Short Circuit to Ground Duration....................................10s
Continuous Input Current into Any Pin .............................±20mA
Continuous Power Dissipation (T
A
= +70°C)
6-Pin TDFN-EP (derate 23.8mW/°C above +70°C)
Multilayer Board ....................................................1904.8mW
8-Pin µMAX (derate 4.8mW/°C above +70°C)
Multilayer Board ......................................................387.8mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature ....................................................+260°C
PACKAGE THERMAL CHARACTERISTICS (Note 1)
TDFN-EP
Junction-to-Ambient Thermal Resistance (θ
JA
) ............42°C/W
Junction-to-Case Thermal Resistance (θ
JC
) ...................9°C/W
µMAX
Junction-to-Ambient Thermal Resistance (θ
JA
) .......206.3°C/W
Junction-to-Case Thermal Resistance
θ
JC
...................42°C/W
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.
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
(V
CC
= +15V, V
EE
= -15V, V
IN+
= V
IN-
= V
GND
= 0V, R
OUT
= 100kΩ to GND, T
A
= -40°C to +125°C, typical values are at T
A
= +25°C,
unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
V
CC
-
1.2
V
T
A
= T
MIN
to T
MAX
Input Offset Voltage
Input Offset Voltage Drift
V
OS
V
OS
- T
C
-40°C
≤
T
A
≤
+25°C
Input Bias Current (Note 3)
I
B
-40°C
≤
T
A
≤
+70°C
-40°C
≤
T
A
≤
+85°C
-40°C
≤
T
A
≤
+125°C
V
CM
= V
EE
to V
CC
- 1.2V,
T
A
= +25°C
V
CM
= V
EE
to V
CC
- 1.4V,
T
A
= T
MIN
to T
MAX
V
EE
+ 0.3V
≤
V
OUT
≤
V
CC
- 0.3V,
R
OUT
= 100kΩ to GND
V
EE
+ 0.75V
≤
V
OUT
≤
V
CC
- 0.75V,
R
OUT
= 10kΩ to GND
78
78
110
110
94
dB
94
130
dB
130
25
mA
T
A
= +25°C
T
A
= T
MIN
to T
MAX
2
50
150
12
55
1.9
V
EE
±0.6
V
CC
-
1.4
±5
±8
mV
µV/°C
fA
pA
pA
nA
UNITS
DC ELECTRICAL CHARACTERISTICS
Guaranteed by
CMRR
T
A
= +25°C
V
EE
Input Voltage Range
V
IN+
, V
IN-
Common-Mode Rejection Ratio
CMRR
Open-Loop Gain
A
OL
Output Short-Circuit Current
I
SC
2
_______________________________________________________________________________________
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +15V, V
EE
= -15V, V
IN+
= V
IN-
= V
GND
= 0V, R
OUT
= 100kΩ to GND, T
A
= -40°C to +125°C, typical values are at T
A
= +25°C,
unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
R
OUT
= 10kΩ to GND
Output Voltage Low
V
OL
R
OUT
= 100kΩ to
GND
R
OUT
= 10kΩ to GND
Output Voltage High
V
OH
R
OUT
= 100kΩ to
GND
f = 1kHz
f = 0.1Hz to 10Hz
f = 100Hz
Input Voltage-Noise Density
Gain Bandwidth
Slew Rate
Capacitive Loading (Note 4)
Total Harmonic Distortion
V
N
GBW
SR
C
LOAD
THD
No sustained oscillations
V
OUT
= 4.5V
P-P
, A
V
= 1V/V,
f = 10kHz, R
OUT
= 10kΩ to GND
Guaranteed by PSRR, V
EE
= 0V
V
CC
- V
EE
= +4.75V to +38V
T
A
= +25°C
T
A
= T
MIN
to T
MAX
+4.75
82
100
400
700
850
f = 1kHz
f = 10kHz
T
A
= T
MIN
to T
MAX
T
A
= T
MIN
to T
MAX
T
A
= T
MIN
to T
MAX
T
A
= T
MIN
to T
MAX
V
CC
-
0.45
V
CC
-
0.15
MIN
TYP
V
EE
+
0.26
V
EE
+
0.05
V
CC
-
0.24
V
V
CC
-
0.03
1
2
25
16.5
15
3
2.2
120
97
MHz
V/µs
pF
dB
nV/√Hz
fA/√Hz
µV
P-P
MAX
V
EE
+
0.45
V
V
EE
+
0.15
UNITS
MAX9945
AC ELECTRICAL CHARACTERISTICS
Input Current-Noise Density
Input Voltage Noise
I
N
V
NP-P
POWER-SUPPLY ELECTRICAL CHARACTERISTICS
Power-Supply Voltage Range
Power-Supply Rejection Ratio
Quiescent Supply Current
V
CC
- V
EE
PSRR
I
CC
+38
V
dB
µA
Note 2:
All devices are 100% production tested at T
A
= +25°C. All temperature limits are guaranteed by design.
Note 3:
Guaranteed by design. IN+ and IN- are internally connected to the gates of CMOS transistors. CMOS GATE leakage is so
small that it is impractical to test in production. Devices are screened during production testing to eliminate defective units.
Note 4:
Specified over all temperatures and process variation by circuit simulation.
_______________________________________________________________________________________
3
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
MAX9945
Typical Operating Characteristics
(V
CC
= +15V, V
EE
= -15V, V
IN+
= V
IN-
= V
GND
= 0V, R
OUT
= 100kΩ to GND, T
A
= -40°C to +125°C, typical values are at T
A
= +25°C,
unless otherwise noted.)
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE AND TEMPERATURE
MAX9945 toc01
OUTPUT VOLTAGE SWING LOW
vs. TEMPERATURE
MAX9945 toc02
OUTPUT VOLTAGE SWING HIGH
vs. TEMPERATURE
MAX9945 toc03
600
0.25
0.25
SUPPLY CURRENT (µA)
500
V
OL
- V
EE
(V)
T
A
= +125°C
400
T
A
= +25°C
300
T
A
= -40°C
200
5
10
15
20
25
30
35
SUPPLY VOLTAGE (V)
0.20
0.20
V
CC
- V
OH
(V)
0.15
I
SINK
= 1.0mA
0.10
I
SINK
= 0.1mA
0.05
0.15
I
SOURCE
= 1.0mA
0.10
I
SOURCE
= 0.1mA
0.05
0
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
0
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
INPUT BIAS CURRENT
vs. TEMPERATURE
MAX9945 toc04
INPUT VOLTAGE
0.1Hz TO 10Hz NOISE
MAX9945 toc05
INPUT VOLTAGE-NOISE DENSITY
vs. FREQUENCY
INPUT VOLTAGE-NOISE DENSITY (nV/ Hz)
MAX9945 toc06
80
70
60
50
I
BIAS
(pA)
40
30
20
10
0
-10
-40
-20
0
20
40
60
80
100 120
TEMPERATURE (°C)
1000
100
10
1s/div
1µV/div
1
10
100
1000
10,000 100,000
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION
vs. FREQUENCY
MAX9945 toc07
TOTAL HARMONIC DISTORTION + NOISE
vs. FREQUENCY
V
CC
- V
EE
= 30V
4.5V
P-P
R
L
= 10kΩ
MAX9945 toc08
-70
V
CC
- V
EE
= 30V,
4.5V
P-P
, R
L
= 10kΩ
-80
-50
-60
THD+N (dB)
THD (dB)
-70
-90
-80
-100
-90
-110
100
1000
10,000
100,000
FREQUENCY (Hz)
-100
10
100
1000
FREQUENCY (Hz)
10,000
100,000
4
_______________________________________________________________________________________
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
Typical Operating Characteristics (continued)
(V
CC
= +15V, V
EE
= -15V, V
IN+
= V
IN-
= V
GND
= 0V, R
OUT
= 100kΩ to GND, T
A
= -40°C to +125°C, typical values are at T
A
= +25°C,
unless otherwise noted.)
INPUT OFFSET VOLTAGE
vs. COMMON-MODE VOLTAGE
MAX9945 toc09
MAX9945
INPUT OFFSET VOLTAGE
vs. TEMPERATURE
V
CM
= V
CC
- 1.2V
INPUT OFFSET VOLTAGE (µV)
800
MAX9945 toc10
1000
1000
INPUT OFFSET VOLTAGE (μV)
800
600
600
V
CM
= 0V
400
400
200
200
V
CM
= V
EE
0
-15
-10
-5
0
5
10
COMMON-MODE VOLTAGE (V)
0
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
OPEN-LOOP GAIN
vs. FREQUENCY
MAX9945 toc11
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
-30
-40
MAX9945 toc12
-20
120
OPEN-LOOP GAIN (dB)
80
CMRR (dB)
1m
1
10
100
1k
10k 100k 1M 10M
-50
-60
-70
40
0
-80
-90
-40
FREQUENCY (Hz)
-100
10
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9945 toc13
RESISTOR ISOLATION
vs. CAPACITIVE LOAD
MAX9945 toc14
0
-20
-40
PSRR (dB)
10,000
UNSTABLE
C
LOAD
(pF)
-60
-80
-100
-120
1
UNIPOLAR
PSRR-
UNIPOLAR
PSRR+
1000
BIPOLAR
PSRR
100
10
100
1k
10k
100k
1M
10M
1
STABLE
10
R
ISO
(Ω)
100
FREQUENCY (Hz)
_______________________________________________________________________________________
5
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