19-4398; Rev 1; 12/10
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).
♦ +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)
PART | TEMP RANGE | PIN- PACKAGE | TOP MARK |
MAX9945ATT+ | -40°C to +125°C | 6 TDFN-EP* | AUE |
MAX9945AUA+ | -40°C to +125°C | 8 µMAX | — |
Medical Pulse Oximetry Photodiode Sensor Interface
Industrial Sensors and Instrumentation
Chemical Sensor Interface
High-Performance Audio Line Out Active Filters and Signal Processing
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
PHOTODIODE
VCC
IN-
MAX9945
OUT
SIGNAL CONDITIONING/ FILTERS
ADC
IN+
VEE
Maxim Integrated Products 1
Supply Voltage (VCC to VEE) ..................................-0.3V to +40V
IN+, IN-, OUT Voltage......................(VEE - 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 (TA = +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
TDFN-EP
Junction-to-Ambient Thermal Resistance (JA) ............42°C/W Junction-to-Case Thermal Resistance (JC) ...................9°C/W
µMAX
Junction-to-Ambient Thermal Resistance (JA) .......206.3°C/W Junction-to-Case Thermal Resistance 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.
(VCC = +15V, VEE = -15V, VIN+ = VIN- = VGND = 0V, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C,
unless otherwise noted.) (Note 2)
PARAMETER | SYMBOL | CONDITIONS | MIN TYP MAX | UNITS | |
DC ELECTRICAL CHARACTERISTICS | |||||
Input Voltage Range | VIN+, VIN- | Guaranteed by CMRR | TA = +25°C | VEE VCC - 1.2 | V |
TA = TMIN to TMAX | VEE VCC - 1.4 | ||||
Input Offset Voltage | VOS | TA = +25°C | ±0.6 ±5 | mV | |
TA = TMIN to TMAX | ±8 | ||||
Input Offset Voltage Drift | VOS - TC | 2 | µV/°C | ||
Input Bias Current (Note 3) | IB | -40°C TA +25°C | 50 150 | fA | |
-40°C TA +70°C | 12 | pA | |||
-40°C TA +85°C | 55 | pA | |||
-40°C TA +125°C | 1.9 | nA | |||
Common-Mode Rejection Ratio | CMRR | VCM = VEE to VCC - 1.2V, TA = +25°C | 78 94 | dB | |
VCM = VEE to VCC - 1.4V, TA = TMIN to TMAX | 78 94 | ||||
Open-Loop Gain | AOL | VEE + 0.3V VOUT VCC - 0.3V, ROUT = 100kΩ to GND | 110 130 | dB | |
VEE + 0.75V VOUT VCC - 0.75V, ROUT = 10kΩ to GND | 110 130 | ||||
Output Short-Circuit Current | ISC | 25 | mA |
(VCC = +15V, VEE = -15V, VIN+ = VIN- = VGND = 0V, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C,
unless otherwise noted.) (Note 2)
PARAMETER | SYMBOL | CONDITIONS | MIN TYP MAX | UNITS | |
Output Voltage Low | VOL | ROUT = 10kΩ to GND | TA = TMIN to TMAX | VEE + VEE + 0.26 0.45 | V |
ROUT = 100kΩ to GND | TA = TMIN to TMAX | VEE + VEE + 0.05 0.15 | |||
Output Voltage High | VOH | ROUT = 10kΩ to GND | TA = TMIN to TMAX | VCC - VCC - 0.45 0.24 | V |
ROUT = 100kΩ to GND | TA = TMIN to TMAX | VCC - VCC - 0.15 0.03 | |||
AC ELECTRICAL CHARACTERISTICS | |||||
Input Current-Noise Density | IN | f = 1kHz | 1 | fA/Hz | |
Input Voltage Noise | VNP-P | f = 0.1Hz to 10Hz | 2 | µVP-P | |
Input Voltage-Noise Density | VN | f = 100Hz | 25 | nV/Hz | |
f = 1kHz | 16.5 | ||||
f = 10kHz | 15 | ||||
Gain Bandwidth | GBW | 3 | MHz | ||
Slew Rate | SR | 2.2 | V/µs | ||
Capacitive Loading (Note 4) | CLOAD | No sustained oscillations | 120 | pF | |
Total Harmonic Distortion | THD | VOUT = 4.5VP-P, AV = 1V/V, f = 10kHz, ROUT = 10kΩ to GND | 97 | dB | |
POWER-SUPPLY ELECTRICAL CHARACTERISTICS | |||||
Power-Supply Voltage Range | VCC - VEE | Guaranteed by PSRR, VEE = 0V | +4.75 +38 | V | |
Power-Supply Rejection Ratio | PSRR | VCC - VEE = +4.75V to +38V | 82 100 | dB | |
Quiescent Supply Current | ICC | TA = +25°C | 400 700 | µA | |
TA = TMIN to TMAX | 850 |
Note 2: All devices are 100% production tested at TA = +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.
SUPPLY CURRENT (A)
(VCC = +15V, VEE = -15V, VIN+ = VIN- = VGND = 0V, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C,
unless otherwise noted.)
600
QUIESCENT SUPPLY CURRENT
MAX9945 toc03
vs. SUPPLY VOLTAGE AND TEMPERATURE
0.25
OUTPUT VOLTAGE SWING LOW vs. TEMPERATURE
MAX9945 toc02
0.25
OUTPUT VOLTAGE SWING HIGH vs. TEMPERATURE
500
400
300
0.20
MAX9945 toc01
VOL - VEE (V)
TA = +125C | ||||||
TA = +25C | ||||||
TA = -40C | ||||||
0.15
0.10
0.05
ISINK
= 0.1mA
ISINK = 1.0mA
0.20
VCC - VOH (V)
0.15
0.10
0.05
ISOURCE = 1.0mA ISOURCE = 0.1mA
200
5
10 15
20 25 30 35
0
-40
-20 0
20 40 60
80 100 120
0
-40
-20 0
20 40 60
80 100 120
80
70
60
IBIAS (pA)
50
40
30
20
10
0
-10
SUPPLY VOLTAGE (V)
MAX9945 toc04
INPUT BIAS CURRENT vs. TEMPERATURE
TEMPERATURE (C)
INPUT VOLTAGE 0.1Hz TO 10Hz NOISE
MAX9945 toc05
INPUT VOLTAGE-NOISE DENSITY (nV/ Hz)
1000
100
10
TEMPERATURE (C)
MAX9945 toc06
INPUT VOLTAGE-NOISE DENSITY vs. FREQUENCY
-40
-20
0 20 40
60 80
100
120
1s/div
1 10
100
1000
10,000 100,000
TEMPERATURE (C)
TOTAL HARMONIC DISTORTION vs. FREQUENCY
-70
VCC - VEE = 30V, 4.5VP-P, RL = 10kΩ
-80
1V/div
-50
-60
FREQUENCY (Hz)
MAX9945 toc08
TOTAL HARMONIC DISTORTION + NOISE vs. FREQUENCY
VCC - VEE = 30V 4.5VP-P
RL = 10kΩ
THD (dB)
-90
MAX9945 toc07
-70
THD+N (dB)
-80
-100
-90
-110
100
1000
10,000
100,000
-100
10
100 1000
10,000
100,000
FREQUENCY (Hz) FREQUENCY (Hz)
(VCC = +15V, VEE = -15V, VIN+ = VIN- = VGND = 0V, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C,
unless otherwise noted.)
1000
INPUT OFFSET VOLTAGE (V)
800
600
400
INPUT OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE
MAX9945 toc09
1000
INPUT OFFSET VOLTAGE (V)
800
600
400
INPUT OFFSET VOLTAGE vs. TEMPERATURE
MAX9945 toc10
VCM = VCC - 1.2V
VCM = 0V
200
0
-15
-10 -5 0
5 10
200
0
-40
-20 0 20
VCM = VEE
40 60 80
100 120
COMMON-MODE VOLTAGE (V) TEMPERATURE (C)
120
OPEN-LOOP GAIN (dB)
80
40
0
MAX9945 toc12
-40
OPEN-LOOP GAIN vs. FREQUENCY
MAX9945 toc11
-20
-30
-40
CMRR (dB)
-50
-60
-70
-80
-90
-100
COMMON-MODE REJECTION RATIO vs. FREQUENCY
1m 1 10 100 1k 10k 100k 1M 10M
10 100 1k 10k
100k 1M
10M
FREQUENCY (Hz)
FREQUENCY (Hz)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
0
10,000
RESISTOR ISOLATION vs. CAPACITIVE LOAD
-20
PSRR (dB)
-40
-60
-80
-100
-120
UNIPOLAR
PSRR-
UNIPOLAR PSRR+
BIPOLAR PSRR
1000
CLOAD (pF)
100
MAX9945 toc13
MAX9945 toc14
UNSTABLE
STABLE
1 10
100 1k
10k
100k 1M
10M
1 10
100
FREQUENCY (Hz)
RISO (Ω)
(VCC = +15V, VEE = -15V, VIN+ = VIN- = VGND = 0V, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C,
unless otherwise noted.)
10,000
OP-AMP STABILITY
vs. CAPACITIVE AND RESISTIVE LOADS
MAX9945 toc15
1000.00
OUTPUT IMPEDANCE vs. FREQUENCY
PARALLEL LOAD CAPACITANCE (pF)
1000
UNSTABLE
100.00
OUTPUT IMPEDANCE (Ω)
MAX9945 toc16
10.00
100
STABLE
1.00
0.10
ACL = 10
A
CL = 1
10
10 100 1000
10,000
0.01
10
100 1k
10k
100k 1M
10M
PARALLEL LOAD RESISTANCE (kΩ) FREQUENCY (Hz)
LARGE-SIGNAL RESPONSE vs. FREQUENCY
LARGE SIGNAL-STEP RESPONSE
MAX9945 toc17
MAX9945 toc18
30
RLOAD
OUTPUT VOLTAGE (VP-P)
25
20
15
= 100kΩ
+5V
VOUT
2.5V/div
AV = 1V/V VIN = 10VP-P
CL = 100pF
RL = 10kΩ
10
-5V
5
0
1 10
100
FREQUENCY (kHz)
1000
10,000
4s/div
LARGE SIGNAL-STEP RESPONSE
MAX9945 toc19
SMALL SIGNAL-STEP RESPONSE
MAX9945 toc20
AV = 1V/V
VIN = 40mVP-P RL = 100kΩ
AV = 1V/V VIN = 2VP-P RL = 10kΩ CL = 100pF
+1V +20mV
VOUT
500mV/div
VOUT
10mV/div
-1V -20mV
1s/div 2s/div
NAME | FUNCTION | ||
1 | 6 | OUT | Amplifier Output |
2 | 4 | VEE | Negative Power Supply. Bypass VEE with 0.1µF ceramic and 4.7µF electrolytic capacitors to quiet ground plane if different from VEE. |
3 | 3 | IN+ | Noninverting Amplifier Input |
4 | 2 | IN- | Inverting Amplifier Input |
5 | 1, 5, 8 | N.C. | No Connection. Not internally connected. |
6 | 7 | VCC | Positive Power Supply. Bypass VCC with 0.1µF ceramic and 4.7µF electrolytic capacitors to quiet ground plane or VEE. |
— | — | EP | Exposed Pad (TDFN Only). Connect to VEE externally. Connect to a large copper plane to maximize thermal performance. Not intended as an electrical connection (TDFN only). |
PIN
TDFN-EP
µMAX
The MAX9945 features a combination of low input cur- rent and voltage noise, rail-to-rail output voltage swing, wide supply voltage range, and low-power operation. The MOS inputs on the MAX9945 make it ideal for use as transimpedance amplifiers and high-impedance sensor interface front-ends in medical and industrial
Rail-to-Rail Output Stage The MAX9945 output stage swings to within 50mV (typ) of either power-supply rail with a 100kΩ load and pro- vides a 3MHz GBW with a 2.2V/µs slew rate. The device is unity-gain stable, and unlike other devices with a low quiescent current, can drive a 120pF capaci- tive load without compromising stability.
applications. The MAX9945 can interface with small Applications Information
signals from either current-sources or high-output
impedance voltage sources. Applications include pho- todiode pulse oximeters, pH sensors, capacitive pres- sure sensors, chemical analysis equipment, smoke detectors, and humidity sensors.
A high 130dB open-loop gain (typ) and a wide supply voltage range, allow high signal-gain implementations prior to signal conditioning circuitry. Low quiescent supply current makes the MAX9945 compatible with portable systems and applications that operate under tight power budgets. The combination of excellent THD, low voltage noise, and MOS inputs also make the MAX9945 ideal for use in high-performance active fil- ters for data acquisition systems and audio equipment.
Low-Current, Low-Noise Input Stage The MAX9945 features a MOS-input stage with only 50fA (typ) of input bias current and a low 1fA/Hz (typ) input current-noise density. The low-frequency input voltage noise is a low 2µVP-P (typ). The input stage accepts a wide common-mode range, extending from the negative supply, VEE, to within 1.2V of the positive supply, VCC.
High-Impedance Sensor Front Ends High-impedance sensors can output signals of interest in either current or voltage form. The MAX9945 inter- faces to both current-output sensors such as photo- diodes and potentiostat sensors, and high-impedance voltage sources such as pH 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 feed- back capacitors help stabilize the amplifier by cancel- ing any zeros in the transfer function created by a 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 photodi- ode dark current if DC accuracy is important. The high bandwidth and slew rate also allows AC signal pro- cessing in certain medical photodiode sensor applica- tions such as pulse oximetry.
1
+
8
-
VOUT
IN+
MAX9945
MAX
+
MAX9945
5
4
IN-
6
3
7
2
Figure 1. Shielding the Inverting Input to Reduce Leakage
10kΩ
IN+
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 a small temperature variation is very important for these applications.
Power-Supply Decoupling The MAX9945 operates from a +4.75V to +38V, VEE ref- erenced power supply. Bypass the power-supply inputs VCC and VEE to a quiet copper ground plane, with a 0.1µF ceramic capacitor in parallel with a 4.7µF electrolytic capacitor, placed close to the leads.
Layout Techniques A good layout is critical to obtaining high performance especially when interfacing with high-impedance sen- sors. Use shielding techniques to guard against para- sitic leakage paths. For transimpedance applications, for example, surround the inverting input, and the traces connecting to it, with a buffered version of its own voltage. A convenient source of this voltage is the noninverting input pin. Pins 1, 5, and 8 on the µMAX package are unconnected, and can be connected to an analog common potential, or to the driven guard potential, to reduce leakage on the inverting input.
A good layout guard rail isolates sensitive nodes, such as the inverting input of the MAX9945 and the traces connecting to it (see Figure 1), from varying or large volt- age differentials that otherwise occur in the rest of the circuit board. This reduces leakage and noise effects, allowing sensitive measurements to be made accurately.
MAX9945
10kΩ
IN-
Figure 2. Input Differential Voltage Protection
Take care to also decrease the amount of stray capaci- tance at the 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. If the sensor is inherently capacitive, or is connected to the amplifier through a long cable, use a low-value feedback capacitor to control high-frequency gain and peaking to stabilize the feedback loop.
Input Differential Voltage Protection During normal op-amp operation, the inverting and non- inverting inputs of the MAX9945 are at approximately the same voltage. The ±12V absolute maximum input differential voltage rating offers sufficient protection for most applications. If there is a possibility of exceeding the input differential voltage specification, in the pres- ence of extremely fast input voltage transients or due to certain application-specific fault conditions, use exter- nal low-leakage pico-amp diodes and series resistors to protect the input stage of the amplifier (see Figure 2). The extremely low input bias current of the MAX9945 allows a wide range of input series resistors to be used. If low input voltage noise is critical to the application, size the input series resistors appropriately.
PROCESS: BiCMOS
OUT
IN+ 3 6
TOP VIEW
+
+
N.C. 1 8 N.C.
OUT 1
6 VCC
IN- 2
MAX9945
7 VCC
VEE 2
MAX9945
5 N.C.
IN+ 3
4 IN-
VEE 4
5 N.C.
EP
µMAX
TDFN
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 TDFN-EP | T633+2 | ||
8 µMAX | U8+1 |
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.
COMMON DIMENSIONS | ||
SYMBOL | MIN. | MAX. |
A | 0.70 | 0.80 |
D | 2.90 | 3.10 |
E | 2.90 | 3.10 |
A1 | 0.00 | 0.05 |
L | 0.20 | 0.40 |
k | 0.25 MIN. | |
A2 | 0.20 REF. |
PACKAGE VARIATIONS | |||||||
PKG. CODE | N | D2 | E2 | e | JEDEC SPEC | b | [(N/2)-1] x e |
T633-2 | 6 | 1.50±0.10 | 2.30±0.10 | 0.95 BSC | MO229 / WEEA | 0.40±0.05 | 1.90 REF |
T833-2 | 8 | 1.50±0.10 | 2.30±0.10 | 0.65 BSC | MO229 / WEEC | 0.30±0.05 | 1.95 REF |
T833-3 | 8 | 1.50±0.10 | 2.30±0.10 | 0.65 BSC | MO229 / WEEC | 0.30±0.05 | 1.95 REF |
T1033-1 | 10 | 1.50±0.10 | 2.30±0.10 | 0.50 BSC | MO229 / WEED-3 | 0.25±0.05 | 2.00 REF |
T1033MK-1 | 10 | 1.50±0.10 | 2.30±0.10 | 0.50 BSC | MO229 / WEED-3 | 0.25±0.05 | 2.00 REF |
T1033-2 | 10 | 1.50±0.10 | 2.30±0.10 | 0.50 BSC | MO229 / WEED-3 | 0.25±0.05 | 2.00 REF |
T1433-1 | 14 | 1.70±0.10 | 2.30±0.10 | 0.40 BSC | - - - - | 0.20±0.05 | 2.40 REF |
T1433-2 | 14 | 1.70±0.10 | 2.30±0.10 | 0.40 BSC | - - - - | 0.20±0.05 | 2.40 REF |
T1433-3F | 14 | 1.70±0.10 | 2.30±0.10 | 0.40 BSC | - - - - | 0.20±0.05 | 2.40 REF |
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.
REVISION NUMBER | REVISION DATE | DESCRIPTION | PAGES CHANGED |
0 | 2/09 | Initial release | — |
1 | 12/10 | Updated Input Bias Current spec in the Electrical Characteristics table and updated Note 3 | 2, 3 |
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.
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