19-5577; Rev 0; 9/10
MAX9638 Evaluation Kit
General Description
The MAX9638 evaluation kit (EV kit) provides a
proven design to evaluate the MAX9638 low-power,
low-noise, CMOS input op amp, which is suitable for
photodiode transimpedance front-ends in portable
medical instruments. The EV kit circuit is preconfigured
as a noninverting amplifier, but can easily be adapted
to other topologies by changing a few components.
The EV kit comes with a MAX9638AVB+ installed.
Op-Amp Configurations
S
Component Pads Allow for Lowpass and
Features
S
Accommodates Noninverting and Differential
Evaluates: MAX9638
Highpass Sallen-Key Filter
S
Proven PCB Layout
S
Fully Assembled and Tested
Ordering Information
PART
TYPE
MAX9638EVKIT+
EV Kit
+Denotes
lead(Pb)-free and RoHS compliant.
Component List
DESIGNATION
C1, C3
QTY
2
DESCRIPTION
0.1FF
Q10%,
16V X7R ceramic
capacitors (0603)
Murata GCM188R71C104K
4.7FF
Q10%,
16V X7R ceramic
capacitors (0805)
Murata GRM21BR71C475K
Not installed, ceramic
capacitors—shorted by PCB
trace (0603)
Not installed, ceramic
capacitors (0603)
3-pin headers
1kI
Q1%
resistors (0603)
DESIGNATION
R3, R4, R7, R9,
R13, R14
R5, R10
R6, R8,
R11, R12
TP1–TP8
U1
—
—
QTY
0
2
4
8
1
4
1
DESCRIPTION
Not installed, resistors (0603)
10kI
Q1%
resistors (0603)
0I
Q5%
resistors (0603)
Red test points
Dual low-power, rail-to-rail I/O
op amp (10 UTQFN)
Maxim MAX9638AVB+
Shunts (JU1–JU4)
PCB: MAX9638 EVALUATION
KIT+
C2, C4
2
C5, C6, C10,
C11, C12, C16
C7, C8, C9,
C13, C14, C15
JU1–JU4
R1, R2,
R15, R16
0
0
4
4
Component Supplier
SUPPLIER
PHONE
WEBSITE
Murata Electronics North America
770-436-1300
www.murata-northamerica.com
Note:
Indicate that you are using the MAX9638 when contacting this component supplier.
_______________________________________________________________
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.
MAX9638 Evaluation Kit
Evaluates: MAX9638
Quick Start
•
•
•
•
MAX9638 EV kit
Precision voltage source
Digital multimeter (DMM)
Detailed Description of Hardware
The MAX9638 EV kit provides a proven design to
evaluate the MAX9638 low-power, low-noise, CMOS
input op amp, which is suitable for photodiode tran-
simpedance front-ends in portable medical instruments.
The EV kit circuit is preconfigured as a noninverting
amplifier, but can easily be adapted to other topologies
by changing a few components.
The device is a single-supply op amp that is ideal for
differential sensing, noninverting amplification, buffering,
and filtering. A few common configurations are shown in
the next few sections.
Noninverting Configuration
The EV kit comes preconfigured as a noninverting ampli-
fier. The gain is set by the ratio of R5 and R1 for op amp
A and R10 and R15 for op amp B. The EV kit comes pre-
configured for a gain of 11 on both op amps. The output
voltage for the noninverting configuration is given by the
equation below:
V
OUTA
=
(1
+
R5
)(V
INAP
+
V
OS
)
R1
and
V
OUTB
=
(1
+
R10
)(V
INBP
+
V
OS
)
R15
Required Equipment
3.3V DC power supply (e.g., Agilent E3620A)
The EV kit is fully assembled and tested. Follow the steps
below to verify board operation:
Procedure
Op-Amp Configurations
1) Connect the positive terminal of the power supply to
the VDD pad and the ground terminal to the nearest
GND and VSS pads.
2) Connect the positive terminal of the precision voltage
source to INAP (TP2). Connect the negative terminal
of the precision voltage source to the GND pad.
3) Connect the INAM (TP1) to the GND pad.
4) Connect the DMM to monitor the voltage on OUTA
(TP4). With the 10kI feedback resistor (R5) and 1kI
series resistor (R1), the gain is 11 (noninverting con-
figuration).
5) Turn on the 3.3V power supply.
6) Apply 100mV from the precision voltage source.
Observe the output at OUTA on the DMM. OUTA
should read approximately 1.1V.
7) Apply 200mV from the precision voltage source.
OUTA should read approximately 2.2V.
Table 1. Jumper Descriptions (JU1–JU4)
JUMPER
JU1
JU2
JU3
JU4
*Default
position.
SHUNT POSITION
1-2*
2-3
1-2*
2-3
1-2*
2-3
1-2*
2-3
DESCRIPTION
Connects
SHDNA
of the device to VDD to put U1-A (op amp A) in normal operation.
Connects
SHDNA
of the device to VSS to put op amp A in shutdown mode.
Connects
SHDNB
of the device to VDD to put U1-B (op amp B) in normal operation.
Connects
SHDNB
of the device to VSS to put op amp B in shutdown mode.
Connects INA+ to INAP (TP2) through R2 and R8.
Connects INA+ to GND through R2 and R8.
Connects INB+ to INBP (TP6) through R12 and R16.
Connects INB+ to GND through R12 and R16.
2
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MAX9638 Evaluation Kit
Evaluates: MAX9638
Differential Amplifier
To configure the EV kit as a differential amplifier, replace
R1, R2, R3, and R5 with appropriate resistors for op
amp A and R9, R10, R15, and R16 for op amp B. When
R1 = R2 and R5 = R3, and R10 = R9 and R15 = R16,
the CMRR of the differential amplifiers is determined by
the matching of the resistor ratios R1/R2 and R3/R5, and
R9/R10 and R15/R16:
V
OUTA
=
GainA (V
INAP
−
V
INAM
)
Lowpass Sallen-Key Filter
To configure the op amp A Sallen-Key as a lowpass
filter, populate the R2 and R8 pads with resistors and
populate the R3 and R4 pads with capacitors. The
corner frequency and Q are then given by:
f
C
=
1
2
π
R
R2
R
R8
C
R3
C
R4
R
R2
R
R8
C
R3
C
R4
C
R4
(R
R2
+
R
R8
)
where:
R5 R3
GainA
=
=
R1 R2
and
V
OUTB
=
GainB (V
INBP
−
V
INBM
)
Q
=
The same idea applies for op amp B by replacing R9,
R12, R14, and R16 with the appropriate components.
Highpass Sallen-Key Filter
To configure the op amp A Sallen-Key as a highpass
filter, populate the R3 and R4 pads with resistors and
populate the R2 and R8 pads with capacitors. The
corner frequency and Q are then given by:
f
C
=
1
2
π
R
R3
R
R4
C
R2
C
R8
R
R3
R
R4
C
R2
C
R8
R
R3
(C
R2
+
C
R8
)
where:
GainB
=
R10 R9
=
R15 R16
Sallen-Key Configuration
The Sallen-Key topology is ideal for filtering sensor
signals with a 2nd-order filter and acting as a buffer.
Schematic complexity is reduced by combining the filter
and buffer operations. The EV kit can be configured in
a Sallen-Key topology by replacing and populating a
few components. The Sallen-Key topology is typically
configured as a unity-gain buffer, which can be done
by replacing R1 and R5 with 0I resistors for op amp
A. The signal is noninverting and applied to INAP. The
filter component pads are R2, R3, R4, and R8, where
some have to be populated with resistors and others with
capacitors. The same idea applies for op amp B; replace
R10 and R15 with 0I resistors and the filter component
pads are R9, R12, R14, and R16.
Q
=
The same idea applies for op amp B by replacing R9,
R12, R14, and R16 with the appropriate components.
Some applications require driving large capacitive loads.
To improve the stability of the amplifiers in such cases,
replace R6 and R11 with a suitable resistor value to
improve amplifier phase margin.
Capacitive Loads
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3
MAX9638 Evaluation Kit
Evaluates: MAX9638
Figure 1. MAX9638 EV Kit Schematic
4
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MAX9638 Evaluation Kit
Evaluates: MAX9638
1.0”
1.0”
Figure 2. MAX9638 EV Kit Component Placement Guide—
Component Side
Figure 3. MAX9638 EV Kit PCB Layout—Component Side
1.0”
Figure 4. MAX9638 EV Kit PCB Layout—Solder Side
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