Rainbow Electronics MAX9945 User Manual
General Description
The MAX9945 operational amplifier features an excellent
combination of low operating power and low input voltage 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 current. The MAX9945 is unity-gain stable and is capable of
rail-to-rail output voltage swing.
The MAX9945 is ideal for portable medical and industrial applications that require low noise analog front-ends
for performance applications such as photodiode transimpedance 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).
Applications
Medical Pulse Oximetry
Photodiode Sensor Interface
Industrial Sensors and Instrumentation
Chemical Sensor Interface
High-Performance Audio Line Out
Active Filters and Signal Processing
Features
♦ +4.75V to +38V Single-Supply Voltage Range
♦ ±2.4V to ±19V Dual-Supply Voltage Range
♦ Rail-to-Rail Output Voltage Swing
♦ 400µA Low Quiescent Current
♦ 50fA Low Input Bias Current
♦ 1fA/
√
√
Hz Low Input Current Noise
♦ 15nV/
√
√
Hz Low Noise
♦ 3MHz Unity-Gain Bandwidth
♦ Wide Temperature Range from -40°C to +125°C
♦ Available in Space-Saving, 6-Pin TDFN Package
(3mm x 3mm)
MAX9945
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
________________________________________________________________
Maxim Integrated Products
1
19-4398; Rev 0; 2/09
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.
Ordering Information
+
Denotes a lead(Pb)-free/RoHS-compliant package.
*
EP = Exposed pad.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
IN-
IN+
OUT
V
EE
V
CC
PHOTODIODE
SIGNAL
CONDITIONING/
FILTERS
ADC
MAX9945
Typical Operating Circuit
PART TEMP RANGE
MAX9945ATT+ -40°C to +125°C 6 TDFN-EP* AUE
MAX9945AUA+ -40°C to +125°C 8 µMAX —
PINPACKAGE
TOP
MARK
MAX9945
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC= +15V, VEE= -15V, V
IN+
= V
IN-
= GND = 0, R
OUT
= 100kΩ to GND, TA= -40°C to +125°C, typical values are at TA= +25°C,
unless otherwise noted.) (Note 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.
Supply Voltage (VCCto VEE) ..................................-0.3V to +40V
IN+, IN-, OUT Voltage......................(V
EE
- 0.3V) to (VCC+ 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
Package Thermal Resistance (Note 1)
θ
JA
..............................................................................42°C/W
θ
JC
................................................................................9°C/W
8-Pin µMAX (derate 4.8mW/°C above +70°C)
Multilayer Board ......................................................387.8mW
Package Thermal Resistance (Note 1)
θ
JA
.........................................................................206.3°C/W
θ
JC
..............................................................................42°C/W
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
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 ELECTRICAL CHARACTERISTICS
Input Voltage Range V
Input Offset Voltage V
Input Offset Voltage Drift V
Input Bias Current (Note 3) I
Common-Mode Rejection Ratio CMRR
Open-Loop Gain A
Output Short-Circuit Current I
Guaranteed by
, V
IN+
IN-
CMRR
TA = +25°C ±0.6 ±5
OS
TA = T
- T
OS
C
B
VCM = VEE to VCC - 1.2V,
T
V
T
V
R
OL
V
R
SC
to T
MIN
= +25°C
A
= VEE to VCC - 1.4V,
CM
= T
A
EE
OUT
EE
OUT
to T
MIN
+ 0.3V ≤ V
= 100kΩ to GND
+ 0.75V ≤ V
= 10kΩ to GND
VCC -
1.2
VCC -
1.4
±8
MAX
TA = +25°C V
= T
MIN
to T
MAX
T
A
EE
V
EE
2 µV/°C
50 fA
78 94
MAX
≤ VCC - 0.3V,
OUT
≤ VCC - 0.75V,
OUT
78 94
110 130
110 130
25 mA
V
mV
dB
dB
MAX9945
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC= +15V, VEE= -15V, V
IN+
= V
IN-
= GND = 0, R
OUT
= 100kΩ to GND, TA= -40°C to +125°C, typical values are at TA= +25°C,
unless otherwise noted.) (Note 2)
Note 2: All devices are 100% production tested at T
A
= +25°C. All temperature limits are guaranteed by design.
Note 3: 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.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Output Voltage Low V
Output Voltage High V
AC ELECTRICAL CHARACTERISTICS
Input Current-Noise Density I
Input Voltage Noise V
Gain Bandwidth GBW 3 MHz
Slew Rate SR 2.2 V/µs
Capacitive Loading (Note 4) C
Total Harmonic Distortion THD
POWER-SUPPLY ELECTRICAL CHARACTERISTICS
Power-Supply Voltage Range VCC - VEEGuaranteed by PSRR, V
Power-Supply Rejection Ratio PSRR VCC - VEE = +4.75V to +38V 82 100 dB
Quiescent Supply Current I
R
OL
R
GND
R
OH
NP-P
LOAD
CC
R
GND
f = 1kHz 1 fA/√Hz
N
f = 0.1Hz to 10Hz 2 µV
f = 100Hz 25
f = 1kHz 16.5Input Voltage-Noise Density V
N
f = 10kHz 15
No sustained oscillations 120 pF
V
f = 10kHz, R
TA = +25°C 400 700
TA = T
= 10kΩ to GND TA = T
OUT
= 100kΩ to
OUT
= 10kΩ to GND TA = T
OUT
= 100kΩ to
OUT
OUT
= 4.5V
MIN
P-P
OUT
to T
, AV = 1V/V,
MAX
= 10kΩ to GND
to T
MIN
MAX
T
= T
to T
MIN
MAX
to T
MIN
MAX
= T
to T
MIN
MAX
= 0 +4.75 +38 V
VCC -
0.45
VCC -
0.15
T
EE
A
A
VEE +
0.26
VEE +
0.05
VCC -
0.24
VCC -
0.03
VEE +
0.45
VEE +
0.15
97 dB
850
V
V
P-P
nV/√Hz
µA
MAX9945
38V, Low-Noise, MOS-Input,
Low-Power Op Amp
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VCC= +15V, VEE= -15V, V
IN+
= V
IN-
= GND = 0, R
OUT
= 100kΩ to GND, TA= -40°C to +125°C, typical values are at TA= +25°C,
unless otherwise noted.)
INPUT BIAS CURRENT
vs. TEMPERATURE
MAX9945 toc04
TEMPERATURE (°C)
I
BIAS
(pA)
100806002040-20
0
10
20
30
40
50
60
70
80
-10
-40 120
µ
INPUT VOLTAGE-NOISE DENSITY
vs. FREQUENCY
MAX9945 toc06
FREQUENCY (Hz)
INPUT VOLTAGE-NOISE DENSITY (nV/ Hz)
10,000 100,000100010010
100
1000
10
1
TOTAL HARMONIC DISTORTION + NOISE
vs. FREQUENCY
MAX9945 toc08
FREQUENCY (Hz)
THD+N (dB)
-90
-80
-70
-60
-50
-100
100,00010,000100 100010
VCC - VEE = 30V
4.5V
P-P
R
L
= 10k
Ω
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE AND TEMPERATURE
600
0.25
OUTPUT VOLTAGE SWING LOW
vs. TEMPERATURE
OUTPUT VOLTAGE SWING HIGH
vs. TEMPERATURE
0.25
500
400
SUPPLY CURRENT (µA)
300
200
5
SUPPLY VOLTAGE (V)
TA = +125°C
TA = +25°C
TA = -40°C
MAX9945 toc01
0.20
0.15
(V)
EE
- V
OL
V
0.10
I
= 0.1mA
SINK
0.05
353025201510
0
-40
TEMPERATURE (°C)
I
SINK
= 1.0mA
MAX9945 toc02
0.20
(V)
0.15
OH
- V
CC
0.10
V
0.05
0
100 120806040200-20
-40
I
SOURCE
I
SOURCE
= 0.1mA
TEMPERATURE (°C)
= 1.0mA
MAX9945 toc03
100 120806040200-20
INPUT VOLTAGE
0.1Hz TO 10Hz NOISE
1s/div
V/div
1
MAX9945 toc05
-70
-80
-90
THD (dB)
-100
-110
TOTAL HARMONIC DISTORTION
vs. FREQUENCY
VCC - VEE = 30V,
, RL = 10kΩ
4.5V
P-P
100
FREQUENCY (Hz)
MAX9945 toc07
100,00010,0001000
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