MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
General Description
The MAX9939 is a general-purpose, differential-input
programmable-gain amplifier (PGA) that is ideal for conditioning a variety of wide dynamic range signals such
as those found in motor current-sense, medical instrumentation, and sonar data acquisition applications. It
features programmable differential gains from 0.2V/V to
157V/V, input offset-voltage compensation, and an output amplifier that can be configured either as a highorder active filter or to provide a differential output.
The PGA is optimized for high-signal bandwidth and its
gain can be programmed to be 0.2V/V, 1V/V, 10V/V,
20V/V, 30V/V, 40V/V, 60V/V, 80V/V, 119V/V, and 157V/V.
Precision resistor matching provides extremely low gain
tempco and high CMRR. Although the MAX9939 operates from a single supply VCC between 2.9V to 5.5V, it
can process signals both above and below ground due
to the use of an input level-shifting amplifier stage.
Furthermore, its inputs are protected to ±16V, allowing it
to withstand fault conditions and signal overranges.
The output amplifier is designed for high bandwidth
and low-bias currents, making it ideal for use in multiple-feedback active filter topologies that offer much
higher Qs and stopband attenuation than Sallen-Key
architectures.
The MAX9939 draws 3.4mA of quiescent supply current
at 5V, and includes a software-programmable shutdown mode that reduces its supply current to only
13µA. The MAX9939 is available in a 10-pin µMAX®
package and operates over the -40°C to +125°C automotive temperature range.
Features
o SPI-Programmable Gains: 0.2V/V to 157V/V
o Extremely Low Gain Tempco
o Integrated Amplifier for R/C Programmable Active
Filter
o Input Offset-Voltage Compensation
o Input Protection to ±16V
o 13µA Software Shutdown Mode
o -40°C to +125°C Operating Temperature Range
o 10-Pin µMAX Package
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX9939AUB+
PART
-40°C to +125°C
10 µMAX
MAX9939AUB/V+T
-40°C to +125°C
10 µMAX
/V denotes an automotive-qualified part.
+Denotes a lead(Pb)-free/RoHS-compliant package.
Applications
Pin Configuration
Sensorless Motor Control
Medical Signal Conditioning
TOP VIEW
Sonar and General Purpose Data Acquisition
Differential to Single-Ended Conversion
+
10 CS
SCLK 1
Differential-Input, Differential-Output Signal
Amplification
DIN
2
GND
3
Sensor Interface and Signal Processing
INAINA+
9
VCC
8
OUTA
4
7
INB
5
6
OUTB
MAX9939
µMAX
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Functional Diagram appears at end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
19-4329; Rev 3; 12/12
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V
INB, OUTA, OUTB, SCLK, DIN, CS............-0.3V to (VCC + 0.3V)
INA+, INA- to GND ..................................................-16V to +16V
Output Short-Circuit Current Duration........................Continuous
Continuous Input Current into Any Terminal.....................±20mA
Continuous Power Dissipation (TA = +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........707mW
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 (reflow) .......................................+260°C
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
(VCC = 5V, VGND = 0V, VINA+ = VINA-, Gain = 10V/V, ROUTA = ROUTB = 1kΩ to VCC/2, TA = TMIN to TMAX, unless otherwise noted.
Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.05
0.38
%
2.2
17
ppm/°C
PGA CHARACTERISTICS
Gain Error
GE
Gain Temperature-Coefficient
Tc-GE
Input Offset Voltage (Note 2)
VOS-A
TA = +25°C, 0.2V ≤ VOUTA ≤ VCC - 0.2V
With no VOS trim, TA = +25°C
1.5
With no VOS trim, TA = TMIN to TMAX
Input Offset-Voltage Drift
10
Input Offset-Voltage Trim Range
Input Common-Mode Range
Common-Mode Rejection Ratio
VCM
CMRR
ISC
Input-Voltage Noise Density
VN
Guaranteed by CMRR test (Note 3)
-1V ≤ VCM ≤ VCC - 2.2V
50
60
-VCC/2 ≤ VCM ≤ VCC - 2.2V, TA = +25°C
50
60
-VCC/2 ≤ VCM ≤ VCC - 2.2V
39
f = 10kHz, gain = 157V/V
Gain = 0.2V/V
GBW
Gain = 1V/V
Gain = 157V/V
Slew Rate
Settling Time
Distortion
Max Capacitive Load
Output Swing
SR
tS
THD
To 1%, 2V output step
f = 1kHz, VOUTA = 2.5VP-P
Voltage output high = VCC - VOUTA,
voltage output low = VOUTA - VGND
V
dB
70
mA
54
nV/√Hz
2.15
MHz
279
9
CL(MAX)
VOH, VOL
mV
VCC
- 2.2
-VCC/2
mV
µV/C
±17
Output Short-Circuit current
Gain-Bandwidth Product
9
15
V/µs
0.45
µs
89
dB
1
nF
25
60
mV
OUTPUT AMPLIFIER CHARACTERISTICS
Input Bias Current
Ib
Input Offset Voltage (Note 2)
VOS-B
Output Short-Circuit Current
ISC
2
(Note 4)
TA = +25°C
1
1.5
TA = TMIN to TMAX
pA
9
15
70
mV
mA
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 5V, VGND = 0V, VINA+ = VINA-, Gain = 10V/V, ROUTA = ROUTB = 1kΩ to VCC/2, TA = TMIN to TMAX, unless otherwise noted.
Typical values are at TA = +25°C.) (Note 1)
PARAMETER
Unity-Gain Bandwidth
Slew Rate
SYMBOL
MAX
UNITS
MHz
6.4
V/µs
tS
VN
Output Swing
TYP
SR
Input-Voltage Noise Density
Max Capacitive Load
MIN
2.2
Settling Time
Distortion
CONDITIONS
UGBW
THD
To 1%, 2V output step
f = 1kHz, VOUTA = 2.5VP-P, gain = -1V/V
CL(MAX)
VOH, VOL
Voltage output high = VCC - VOUTB,
voltage output low = VOUTB - VGND
0.86
µs
36
nV/√Hz
90
dB
1
nF
25
60
mV
5.5
V
POWER SUPPLY
Supply Voltage Range
Power-Supply Rejection Ratio
Supply Current
Shutdown Supply Current
VCC
PSRR
Guaranteed by PSRR
2.9
1kΩ between OUTA and INB, 1kΩ between
OUTB and INB, measured differentially
between OUTA and OUTB
60
80
dB
ICC
OUTA and OUTB unloaded
3.4
6.7
mA
ISHDN
Soft shutdown through SPI
13
24
µA
0.8
V
SPI CHARACTERISTICS
Input-Voltage Low
VIL
Input-Voltage High
VIH
Input Leakage Current
IIN
Input Capacitance
CIN
VCC = 5V
2.0
VCC = 3.3V
1.65
V
±1
5
µA
pF
SPI TIMING CHARACTERISTICS
SCLK Frequency
fSCLK
(Note 5)
5
MHz
SCLK Period
tCP
200
ns
SCLK Pulse-Width High
tCH
80
ns
SCLK Pulse-Width Low
tCL
80
ns
CS Fall to SCLK Rise Setup
tCSS
80
ns
CS Fall to SCLK Rise Hold
DIN to SCLK Setup
tCSH
tDS
20 + (0.5
x tCP)
55
ns
ns
DIN Hold after SCLK
tDH
0
ns
SCLK Rise to CS Fall Delay
tCS0
20
ns
CS Rise to SCLK Rise Hold
tCS1
80
ns
CS Pulse-Width High
tCSW
200
ns
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
All devices are 100% production tested at TA = +25°C. Temperature limits are guaranteed by design.
The input offset voltage includes the effects of mismatches in the internal VCC/2 resistor dividers.
For gain of 0.25V/V, the input common-mode range is -1V to VCC - 2V.
The input current of a CMOS device is too low to be accurately measured on an ATE and is typically on the order of 1pA.
Parts are functional with fSCLK = 10MHz.
Maxim Integrated
3
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
CS
tCSW
tCSS
tCL
tCSO
tCP
tCH
tCSH
tCS1
SCLK
tDS
tDH
DIN
Figure 1. SPI Interface Timing Diagram
Typical Operating Characteristics
(VCC = 5V, VGND = 0V, VIN+ = VIN- = 0V, Gain = 10V/V, ROUTA = ROUTB = 1kΩ to VCC/2, TA = +25°C, unless otherwise noted.)
2
1V/V ≤ GAIN ≤ 157V/V
RL = 10kΩ to VCC/2
1
0
-20
-40
20
GAIN =30V/V
0
-1
-2
-60
RL = 10kΩ to VCC/2
40
GAIN (dB)
GAIN (dB)
GAIN (dB)
20
60
MAX9939 toc02
MAX9939 toc01
40
AMPLIFIER B GAIN vs. FREQUENCY
PGA GAIN vs. FREQUENCY
3
MAX9939 toc03
PGA GAIN vs. FREQUENCY
60
0
-20
-40
GAIN = 160V/V
-60
-3
RL = 10kΩ to VCC/2
0.1
1
10
100
0.01
1
AMPLIFIER B GAIN vs. FREQUENCY
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
RL = 10kΩ to VCC/2
1V/V ≤ GAIN ≤ 157V/V
-10
-1
-30
-40
0.10
0.05
-60
-3
100
0.15
-50
-2
10
GAIN ERROR vs. TEMPERATURE
GAIN ERROR (%)
CMRR (dB)
0
1
0.20
-20
1
0.1
FREQUENCY (MHz)
MAX9939 toc05
MAX9939 toc04
0
0.01
10
FREQUENCY (MHz)
2
GAIN (dB)
0.1
FREQUENCY (MHz)
3
-70
-4
0.01
0.1
1
FREQUENCY (MHz)
4
-80
-4
0.01
MAX9939 toc06
-80
10
-80
0.001
0
0.01
0.1
1
FREQUENCY (MHz)
10
100
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Typical Operating Characteristics (continued)
(VCC = 5V, VGND = 0V, VIN+ = VIN- = 0V, Gain = 10V/V, ROUTA = ROUTB = 1kΩ to VCC/2, TA = +25°C, unless otherwise noted.)
INPUT VOS vs. TEMPERATURE
INPUT VOS TRIM RESPONSE
MAX9939 toc08
MAX9939 toc07
3.0
OFFSET (mV)
2.5
2.0
OUTA
10mV/div
1.5
1.0
0.5
GAIN = 1V/V
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
1ms/div
TEMPERATURE (°C)
10V/V ≤ GAIN ≤ 157V/V
-40
-60
1V/V ≤ GAIN ≤ 157V/V
-20
DISTORTION (dB)
-20
PSRR (dB)
0
MAX9939 toc09
0
MAX9939 toc10
TOTAL HARMONIC DISTORTION
vs. FREQUENCY
DIFFERENTIAL PSRR vs. FREQUENCY
-40
GAIN = 157V/V
-60
-80
-80
-100
-100
-120
GAIN = 1V/V
1
0.1
10
100
0.01
1000 10,000
0.1
100
1000
MAX9939 toc11
AMPLIFIER B
NOISE DENSITY (nV/√Hz)
PGA
10V/V ≤ GAIN ≤ 157V/V
NOISE DENSITY (nV/√Hz)
10
NOISE VOLTAGE DENSITY
NOISE VOLTAGE DENSITY
10,000
1000
100
100
10
10
10
100
1000
FREQUENCY (Hz)
Maxim Integrated
1
FREQUENCY (kHz)
FREQUENCY (kHz)
MAX9939 toc12
0.01
10,000
100,000
10
100
1000
10,000
100,000
FREQUENCY (Hz)
5
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Typical Operating Characteristics (continued)
(VCC = 5V, VGND = 0V, VIN+ = VIN- = 0V, Gain = 10V/V, ROUTA = ROUTB = 1kΩ to VCC/2, TA = +25°C, unless otherwise noted.)
MAX9939 toc13
1000
AMPLIFIER B
800
SETTLING TIME (ns)
IMPEDANCE (Ω)
10
1
0.1
VOUT = 2VP-P
900
MAX9939 toc14
1% SETTLING TIME vs. GAIN (PGA)
OUTPUT IMPEDANCE vs. FREQUENCY
100
700
600
500
400
300
200
100
0.01
0.001
0
0.01
0.1
1
10
0
20
40
60
80
100 120 140 160
GAIN (V/V)
FREQUENCY (MHz)
RECOVERY FROM INPUT OVERLOAD
(PGA, GAIN = 157V/V)
RECOVERY FROM INPUT OVERLOAD
(PGA, GAIN = 1V/V)
MAX9939 toc16
MAX9939 toc15
INA+ - INA2V/div
INA+ - INA2mV/div
OUTA
1V/div
OUTA
1V/div
400ns/div
1µs/div
RECOVERY FROM INPUT OVERLOAD
(OUTPUT AMPLIFIER)
GAIN ADJUST RESPONSE
MAX9939 toc17
MAX9939 toc18
IN
2V/div
INA+ - INA2mV/div
GAIN = 10V/V
OUTB
2V/div
OUTA
1V/div
GAIN = 1V/V
GAIN = 40V/V
GAIN = 157V/V
1µs/div
6
200µs/div
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Typical Operating Characteristics (continued)
(VCC = 5V, VGND = 0V, VIN+ = VIN- = 0V, Gain = 10V/V, ROUTA = ROUTB = 1kΩ to VCC/2, TA = +25°C, unless otherwise noted.)
COMMON-MODE REJECTION RESPONSE
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
MAX9939 toc19
INA+
1V/div
INA1V/div
OUTA
2V/div
SHUTDOWN CURRENT (µA)
VCM = 1VP-P, 1kHz
VDM = 25mVP-P, 10kHz
MAX9939 toc20
20
16
12
8
4
GAIN = 157V/V
0
200µs/div
2.8
3.2
3.6
4.0
4.4
4.8
5.2
VOLTAGE (V)
Pin Description
PIN
NAME
FUNCTION
1
SCLK
2
DIN
Serial-Data Input. Data is clocked into the serial interface on the rising edge of SCLK.
3
GND
Ground
4
INA-
PGA Inverting Input
5
INA+
PGA Noninverting Input
6
OUTB
7
INB
Buffer Input
8
OUTA
PGA Output
9
VCC
Power Supply. Bypass to GND with 0.1µF and 1µF capacitors.
10
CS
Active-Low Chip-Select Input. Drive CS low to enable the serial interface. Drive CS high to disable the serial interface.
Serial-Clock Input
Buffer Output
Detailed Description
The MAX9939 is a general-purpose PGA with input offset trim capability. Its gain and input offset voltage
(VOS) are SPI programmable. The device also includes
an uncommitted output operational amplifier that can
be used as either a high-order active filter or to provide
a differential output. The device can be put into shutdown through SPI.
The gain of the amplifier is programmable between
0.2V/V and 157V/V. The input offset is programmable
between ±17mV and can be used to regain output
dynamic range in high gain settings. An input offset-voltage measurement mode enables input offset voltage to
Maxim Integrated
be calibrated out in firmware to obtain excellent DC
accuracy.
The main amplifier accepts a differential input and provides a single-ended output. The relationship between
the differential input and singled-ended output is given
by the representative equation:
VOUTA = VCC/2 - Gain x (VINA+ - VINA-) + Gain x VOS
Architecture
The MAX9939 features three internal amplifiers as
shown in the Functional Diagram. The first amplifier
(amplifier LVL) is configured as a differential amplifier
for differential to single-ended conversion with an input
offset-voltage trim network. It has extremely high
7
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
CS
SCLK
DIN
D0
D1
D2
D3
D6
D5
D6
D7
Figure 2. SPI Interface Timing Diagram (CPOL = CPHA = 0)
CMRR, gain accuracy, and very low temperature drift
due to precise resistor matching. The output of this
amplifier is level shifted to VCC/2.
This amplifier is followed by a programmable-gain
inverting amplifier (amplifier A) with programmable RF
and RI resistors whose gain varies between 0.2V/V and
157V/V. The output of this amplifier is biased at
VCC/2 and has extremely high gain accuracy and low
temperature drift.
The MAX9939 has an uncommitted op amp (amplifier
B) whose noninverting input is referenced to VCC/2. Its
inverting input and output are externally accessible,
allowing it to be configured either as an active filter or
as a differential output.
A robust input ESD protection scheme allows input voltages at INA+ and INA- to reach ±16V without damaging the MAX9939, thus making the part extremely
attractive for use in front-ends that can be exposed to
high voltages during fault conditions. In addition, its
input-voltage range extends down to -VCC/2 (e.g., -2.5V
when powered from a 5V single supply) allowing the
MAX9939 to translate below ground signals to a 0V to
5V output signal. This feature simplifies interfacing
ground-referenced signals with unipolar-input ADCs.
SPI-Compatible Serial Interface
The MAX9939 has a write-only interface, consisting of
three inputs: the clock signal (SCLK), data input (DIN),
and chip-select input (CS). The serial interface works
with the clock polarity (CPOL) and clock phase (CPHA)
both set to 0 (see Figure 1). Initiating a write to the
MAX9939 is accomplished by pulling CS low. Data is
clocked in on the rising edge of each clock pulse, and
is written LSB first. Each write to the MAX9939 consists
8
of 8 bits (1 byte). Pull CS high after the 8th bit has been
clocked in to latch the data and before sending the
next byte of instruction. Note that the internal register is
not updated if CS is pulled high before the falling edge
of the 8th clock pulse.
Register Description
The MAX9939 consists of three registers: a shift register
and two internal registers. The shift register accepts
data and transfers it to either of the two internal registers. The two internal registers store data that is used to
determine the gain, input offset voltage, and operating
modes of the amplifier. The two internal registers are the
Input VOS Trim register and Gain register. The format of
the 8-bit write to these registers is shown in Tables 1
and 2. Data is sent to the shift register LSB first.
SEL: The SEL bit selects which internal register is written to. Set SEL to 0 to write bits D5:D1 to the input VOS
trim register. Set SEL to 1 to write D4:D1 to the Gain
register (D5 is don’t care when SEL = 1).
Table 1. Input VOS Trim Register
D7
MSB
D6
SHDN MEAS
D5
D4
D3
D2
D1
D0
LSB
V4
V3
V2
V1
V0
SEL = 0
Table 2. Gain Register
D7
MSB
D6
SHDN MEAS
D5
D4
D3
D2
D1
D0
LSB
X
G3
G2
G1
G0
SEL = 1
X = Don’t care.
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
SHDN: Set SHDN to 0 for normal operation. Set SHDN
to 1 to place the device in a low-power 13µA shutdown
mode. In shutdown mode, the outputs OUTA and OUTB
are high impedance, however, the SPI decode circuitry
is still active. Each instruction requires a write to the
SHDN bit.
MEAS: The MAX9939 provides a means for measuring
its own input offset voltage. When MEAS is set to 1, the
INA- input is disconnected from the input signal path
and internally shorted to INA+. This architecture thus
allows the input common-mode voltage to be compensated at the application-specific input common-mode
voltage of interest. The input offset voltage of the PGA
is the output offset voltage divided by the programmed
gain without any VOS trim (i.e., V3:V0 set to 0):
VOS-INHERENT = (VOUTA - VCC/2)/Gain
Program VOS to offset VOS-INHERENT. The input VOS
also includes the effect of mismatches in the resistordividers. Setting MEAS to 0 switches the inputs back to
the signals on INA+ and INA-. Each instruction requires
a write to the MEAS bit.
Programming Gain
The PGA’s gain is set by the bits G3:G0 in the Gain register. Table 3 shows the relationship between the bits
G3:G0 and the amplifier’s gain. The slew rate and
small-signal bandwidth (SSBW) of the PGA depend on
its gain setting as shown in Table 3.
Programming Input Offset Voltage (VOS)
The input offset voltage is set by the bits V4:V0 in the
Input Offset Voltage Trim register. Bit V4 determines the
polarity of the offset. Setting V4 to 0 makes the offset
positive, while setting V4 to 1 makes the offset negative.
Table 4 shows the relationship between V3:V0 and VOS.
To determine the effect of VOS at the output of the amplifier for gains other than 1, use the following formula:
VOUTA = VCC/2 + Gain x (VOS-INHERENT + VOS)
where VOS-INHERENT is the inherent input offset voltage
of the amplifier, which can be measured by setting
MEAS to 1.
Applications Information
Use of Output Amplifier as Active Filter
The output amplifier can be configured as a multiplefeedback active filter as shown in Figure 3, which traditionally has better stopband attenuation characteristics
than Sallen-Key filters. These filters also possess inherently better distortion performance since there are no
common-mode induced effects (i.e., the commonmode voltage of the operational amplifier is always
fixed at VCC/2 instead of it being signal dependent
such as in Sallen-Key filters). Choose external resistors
and capacitors to create lowpass, bandpass, or highpass filters.
Table 3. Gain
G3:G0
GAIN
(V/V)
SLEW RATE
(V/µs)
SMALL-SIGNAL BANDWIDTH (MHz)
0000
1
2.90
2.15
0001
10
8.99
2.40
0010
20
8.70
1.95
0011
30
12.80
3.40
0100
40
12.50
2.15
0101
60
13.31
2.60
0110
80
12.15
1.91
0111
120
18.53
2.30
1000
157
16.49
1.78
2.86
1.95
2.90
2.15
1001
1010
Maxim Integrated
0.2 (VCC = 5V)
0.25 (VCC = 3.3V)
1
9
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Table 4. Input Offset-Voltage Trim
INPUT OFFSET VOLTAGE
(V4 = 0 TRIMS POSITIVE, V4 = 1 TRIMS NEGATIVE)
V3:V0
VOS (mV)
0000
0
0001
1.3
0010
2.5
0011
3.8
0100
4.9
0101
6.1
0110
7.3
0111
8.4
1000
10.6
1001
11.7
1010
12.7
1011
13.7
1100
14.7
1101
15.7
1110
16.7
1111
17.6
Use of Output Operational Amplifier as TIA
CMOS inputs on the output op amp makes it ideal for
use as an input transimpedance amplifier (TIA) in certain current-output sensor applications. In such a situation, keep in mind that the inverting input operates at
fixed voltage of VCC/2. Use a high-value resistor as a
feedback gain element, and use a feedback capacitor
in parallel with this resistor if necessary to aid amplifier stability in the presence of high photodiode or
cable capacitance. The output of this TIA can be routed to INA+ or INA- for further processing and signal
amplification.
Power-Supply Bypassing
Bypass VCC to GND with a 0.1µF capacitor in parallel
with a 1µF low-ESR capacitor placed as close as possible to the MAX9939.
Differential-Input, Differential-Output PGA
The output amplifier can be configured so that the
MAX9939 operates as a differential-input, differentialoutput programmable gain amplifier. As shown in
Figure 4, use a 10kΩ resistor between OUTA and INB,
and between INB and OUTB. Such a differential-output
configuration is ideal for use in low-voltage applications
that can benefit from the 2X output voltage dynamic
range when compared to single-ended output format.
10
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
VCC
1µF
0.1µF
VCC
MAX9939
VCC
20kΩ
20kΩ
VCC/2
VCC/2
20kΩ
20kΩ
10kΩ
INA+
OUTA
A
RI
LVL
10kΩ
66.5kΩ
RF
INA-
ASIC
INB
121kΩ
VCC
10kΩ
220pF
GAIN
INPUT
OFFSETVOLTAGE
TRIM
DIN
66.5kΩ
1.21kΩ
20kΩ
B
SHUTDOWN
SPI REGISTERS
SCLK
4.7nF
ADC
OUTB
100nF
20kΩ
VCC/2
CS
GND
CS
DOUT
SCLK
Figure 3. Using the MAX9939 Output Amplifier as an Anti-Aliasing Filter (Corner Frequency = 1.3kHz) to Maximize Nyquist Bandwidth
Maxim Integrated
11
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
VCC
1µF
0.1µF
VCC
MAX9939
VCC
20kΩ
20kΩ
VCC/2
VCC/2
20kΩ
20kΩ
10kΩ
INA+
OUTA
A
RI
LVL
10kΩ
10kΩ
RF
INA-
ASIC
INB
VCC
10kΩ
10kΩ
GAIN
INPUT
OFFSETVOLTAGE
TRIM
20kΩ
B
SHUTDOWN
ADC
OUTB
VCC/2
SPI REGISTERS
SCLK
DIN
20kΩ
CS
GND
CS
DOUT
SCLK
Figure 4. Using the MAX9939 as a Differential-Input, Differential-Output PGA
Chip Information
PROCESS: BiCMOS
12
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Functional Diagram
VCC
VCC
MAX9939
VCC
20kΩ
20kΩ
VCC/2
VCC/2
20kΩ
20kΩ
10kΩ
INA+
OUTA
A
RI
LVL
10kΩ
RF
INA-
INB
VCC
10kΩ
GAIN
INPUT
OFFSETVOLTAGE
TRIM
20kΩ
B
OUTB
SHUTDOWN
VCC/2
SPI REGISTERS
SCLK
DIN
20kΩ
CS
GND
Maxim Integrated
13
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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.
10 µMAX
U10+2
21-0061
90-0330
α
α
14
Maxim Integrated
MAX9939
SPI Programmable-Gain Amplifier
with Input VOS Trim and Output Op Amp
Revision History
REVISION
NUMBER
REVISION
DATE
0
11/08
Initial release
—
1
2/09
Corrected gain value in Table 3
9
2
12/10
Modified Figure 2
8
3
12/12
Added the MAX9939AUB/V+T
1
DESCRIPTION
PAGES
CHANGED
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 ________________________________ 15
© 2012 Maxim Integrated Products, Inc.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
工商网监
湘ICP备2023018690号
