Evaluates: MAX44251
MAX44251 Evaluation Kit
General Description
The MAX44251 evaluation kit (EV kit) provides a proven
design to evaluate the MAX44251 dual low-power, low-
drift operational amplifier (op amp) in an 8-pin SOT23
package. The EV kit circuit is preconfigured as noninvert-
ing amplifiers, but can be adapted to other topologies by
changing a few components. Low power, low drift, input
offset voltage, and rail-to-rail input/output stages make
this device ideal for applications requiring ultra-low
noise and DC precision. The component pads accom-
modate 0805 packages, making them easy to solder
and replace. The EV kit comes with a MAX44251AKA+
installed.
S
Rail-to-Rail Inputs/Outputs
S
Accommodates Easy-to-Use 0805 Components
S
2.7V to 20V Power-Supply Range
S
Proven PCB Layout
S
Fully Assembled and Tested
Features
S
Accommodates Multiple Op-Amp Configurations
Ordering Information
PART
MAX44251EVKIT#
#Denotes
RoHS compliant.
TYPE
EV Kit
Component List
DESIGNATION
C1, C3
QTY
2
DESCRIPTION
0.1FF
Q10%,
25V X7R ceramic
capacitors (0805)
Murata GRM21BR71E104K
4.7FF
Q10%,
25V X5R ceramic
capacitors (0805)
Murata GRM21BR61E475K
capacitors (0805)
U1
6
2
4
2-pin headers, 0.1in centers
—
3-pin headers, 0.1in centers
1kI
Q1%
resistors (0805)
—
8
1
1
DESIGNATION
R3, R4, R7, R13,
R14, R17
R5, R15
R6, R8, R16,
R18
TP1, TP2
QTY
0
2
4
0
DESCRIPTION
Not installed, resistors (0805)
10kI
Q1%
resistors (0805)
0I
Q5%
resistors (0805)
Not installed, miniature test
points
Dual low-power, rail-to-rail I/O
op amp (8 SOT23)
Maxim MAX44251AKA+
Shunts
PCB: MAX44251 EVALUATION
KIT
C2, C4
C5–C10,
C15–C20
JU1, JU2, JU4,
JU11, JU12,
JU14
JU3, JU13
R1, R2, R11,
R12
2
0
Functional
ceramic
Not installed,
Diagrams
Component Supplier
SUPPLIER
Murata Electronics North America, Inc.
PHONE
770-436-1300
WEBSITE
www.murata-northamerica.com
Note:
Indicate that you are using the MAX44251 when contacting this component supplier.
Pin Configurations appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
19-6285; Rev 0; 4/12
Evaluates: MAX44251
MAX44251 Evaluation Kit
Quick Start
•
•
•
•
MAX44251 EV kit
+5V, 10mA DC power supply (PS1)
Two precision voltage sources
Two digital multimeters (DMMs)
4)
5)
Connect INAM to GND.
Connect the positive terminal of the second preci-
sion voltage source to the INBP pad. Connect the
negative terminal of the precision voltage source to
GND.
6) Connect INBM to GND.
5) Connect the DMMs to monitor the voltages on OUTA
and OUTB. With the 10kω feedback resistors and
1kω series resistors, the gain of each noninverting
amplifier is +11.
8) Turn on the +5V power supply.
9) Apply 100mV from the precision voltage sources.
Observe the output at OUTA and OUTB on the
DMMs. Both should read approximately +1.1V.
10) Apply 400mV from the precision voltage sources.
Both OUTA and OUTB should read approximately
+4.4V.
Required Equipment
The EV kit is fully assembled and tested. Follow the steps
below to verify board operation:
1) Verify that the jumpers are in their default position,
as shown in Table 1.
2) Connect the positive terminal of the +5V supply to
VDD and the negative terminal to GND and VSS.
3) Connect the positive terminal of the precision volt-
age source to INAP. Connect the negative terminal
of the precision voltage source to GND.
Procedure
Table 1. Jumper Descriptions
JUMPER
JU1
SHUNT POSITION
Installed*
Open
Installed*
JU2
Open
1-2*
2-3
Installed*
JU4
Open
Installed*
JU11
Open
Installed*
JU12
Open
1-2*
2-3
Installed*
JU14
*Default
position.
Open
DESCRIPTION
Connects INAM to R1. Also shorts capacitor C5.
Connects INAM to R1 through capacitor C5. When AC-coupling is desired, remove the
shunt and install capacitor C5.
Connects INAP to JU3 position 1. Also shorts capacitor C6.
Connects INAP to JU3 position 1 through capacitor C6. When AC-coupling is desired,
remove the shunt and install capacitor C6.
Connects INAP to JU2 and C6 through R2 and R8
Connects INAP to GND through R2 and R8
Connects OUTA to OUTA
Connects OUTA to OUTA through capacitor C10. When AC-coupling is desired, remove
the shunt and install capacitor C10.
Connects INBM to R11. Also shorts capacitor C15.
Connects INBM to R11 through capacitor C15. When AC-coupling is desired, remove the
shunt and install capacitor C15.
Connects INBP to JU13 position 1. Also shorts capacitor C16.
Connects INBP to JU13 position 1 through capacitor C16. When AC-coupling is desired,
remove the shunt and install capacitor C16.
Connects INBP to JU12 and C16 through R12 and R18
Connects INBP to GND through R12 and R18
Connects OUTB to OUTB
Connects OUTB to OUTB through capacitor C20. When AC-coupling is desired, remove
the shunt and install capacitor C20.
JU3
JU13
2
Maxim Integrated
Evaluates: MAX44251
MAX44251 Evaluation Kit
Detailed Description of Hardware
The MAX44251 EV kit provides a proven layout for the
MAX44251 low-power, low-drift dual op amp. The IC is an
ultra-high-precision, dual op amp with a high supply volt-
age range designed for load cell, medical instrumenta-
tion, and precision instrumentation applications. Various
test points are included for easy evaluation.
The IC is a single-supply dual op amp whose primary
application is operating in the noninverting configuration;
however, the IC can operate with a dual supply as long
as the voltage across the VDD and GND pins of the IC do
not exceed the absolute maximum ratings. When operat-
ing with a single supply, short VSS to GND.
The IC is a single-supply dual op amp that is ideal for
differential sensing, noninverting amplification, buffering,
and filtering. A few common configurations are shown in
the next few sections.
The following sections explain how to configure one
of the device’s op amps (op-amp A). To configure the
device’s second op amp (op-amp B), the same equa-
tions can be used after modifying the component refer-
ence designators. For op-amp B, the equations should
be modified by adding 10 to the number portion of the
reference designators (e.g., for the noninverting configu-
ration, equation R1 becomes R11 and R5 becomes R15).
Noninverting Configuration
The EV kit comes preconfigured as a noninverting ampli-
fier. The gain is set by the ratio of R5 and R1. The EV kit
comes preconfigured for a gain of 11. The output voltage
for the noninverting configuration is given by the equa-
tion below:
R5
V
OUTA
=
(1
+
) V
INAP
R1
Differential Amplifier
To configure the EV kit as a differential amplifier, replace
R1, R2, R3, and R5 with appropriate resistors. When R1
= R2 and R3 = R5, the CMRR of the differential amplifier
is determined by the matching of the resistor ratios R1/
R2 and R3/R5.
=
GAIN (V
INAP
−
V
INAM
)
V
OUTA
where:
GAIN
=
R5 R3
=
R1 R2
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 and short JU2. The
noninverting signal is applied to the INAP test point with
JU2 short and short pins 1-2 on JU3 or do the same on
the INBP PCB pad similarly. The filter component pads
are R2, R3, R4, and R8, where some have to be popu-
lated with resistors and others with capacitors.
Lowpass Sallen-Key Filter
To configure the 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
Op-Amp Configurations
C
R3
(R
R2
+
R
R8
)
Highpass Sallen-Key Filter
To configure the 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
R4
(C
R2
+
C
R8
)
Q
=
Q
=
Transimpedance Application
To configure op-amp U1-A as a transimpedance ampli-
fier (TIA), replace R1 with a 0I resistor and install a
shunt on jumper JU1 and shunt on pins 2-3 on jumper
JU3. The output voltage of the TIA is the input current
multiplied by the feedback resistor:
V
OUT
= (I
IN
+ I
BIAS
) x R4 + V
OS
where R4 is installed as a 10kI resistor, I
IN
is defined
as the input current source applied at the INAM PCB
pad, I
BIAS
is the input bias current, and V
OS
is the input
offset voltage of the op amp. Use capacitor C8 (and
C7, if applicable) to stabilize the op amp by rolling off
high-frequency gain due to a large cable capacitance.
Similarly, we can configure op-amp U1-B for transimped-
ance application.
Capacitive Loads
Some applications require driving large capacitive loads.
To improve the stability of the amplifier, replace R6 (R16
for U1-B) with a suitable resistor value to improve ampli-
fier phase margin. The R6/C9 (R16/C19 for U1-B) filter
can also be used as an anti-alias filter, or to limit amplifier
3
Sallen-Key Filter Configuration
The Sallen-Key filter topology is ideal for filtering sensor
signals with a second-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
Maxim Integrated
Evaluates: MAX44251
MAX44251 Evaluation Kit
Figure 1. MAX44251 EV Kit Schematic
4
Maxim Integrated
Evaluates: MAX44251
MAX44251 Evaluation Kit
1.0”
1.0”
Figure 2. MAX44251 EV Kit Component Placement Guide—
Component Side
Figure 3. MAX44251 EV Kit PCB Layout—Component Side
1.0”
Figure 4. MAX44251 EV Kit PCB Layout—Solder Side
Maxim Integrated
5
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