Functional Diagrams
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.
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.
Features
S Accommodates Multiple Op-Amp Configurations
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
Ordering Information
#Denotes RoHS compliant.
Component List
Component Supplier
Note: Indicate that you are using the MAX44251 when contacting this component supplier.
PART TYPE
MAX44251EVKIT# EV Kit
SUPPLIER PHONE WEBSITE
Murata Electronics North America, Inc. 770-436-1300 www.murata-northamerica.com
DESIGNATION QTY DESCRIPTION
C1, C3 2
0.1FF Q10%, 25V X7R ceramic
capacitors (0805)
Murata GRM21BR71E104K
C2, C4 2
4.7FF Q10%, 25V X5R ceramic
capacitors (0805)
Murata GRM21BR61E475K
C5–C10,
C15–C20 0Not installed, ceramic
capacitors (0805)
JU1, JU2, JU4,
JU11, JU12,
JU14
62-pin headers, 0.1in centers
JU3, JU13 23-pin headers, 0.1in centers
R1, R2, R11,
R12 41kI Q1% resistors (0805)
DESIGNATION QTY DESCRIPTION
R3, R4, R7, R13,
R14, R17 0Not installed, resistors (0805)
R5, R15 210kI Q1% resistors (0805)
R6, R8, R16,
R18 40I Q5% resistors (0805)
TP1, TP2 0Not installed, miniature test
points
U1 1
Dual low-power, rail-to-rail I/O
op amp (8 SOT23)
Maxim MAX44251AKA+
— 8 Shunts
— 1 PCB: MAX44251 EVALUATION
KIT
Evaluates: MAX44251
19-6285; Rev 0; 4/12
MAX44251 Evaluation Kit
Table 1. Jumper Descriptions
Quick Start
Required Equipment
• MAX44251 EV kit
• +5V, 10mA DC power supply (PS1)
• Two precision voltage sources
• Two digital multimeters (DMMs)
Procedure
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.
4) Connect INAM to GND.
5) 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.
*Default position.
JUMPER SHUNT POSITION DESCRIPTION
JU1
Installed* Connects INAM to R1. Also shorts capacitor C5.
Open Connects INAM to R1 through capacitor C5. When AC-coupling is desired, remove the
shunt and install capacitor C5.
JU2
Installed* Connects INAP to JU3 position 1. Also shorts capacitor C6.
Open Connects INAP to JU3 position 1 through capacitor C6. When AC-coupling is desired,
remove the shunt and install capacitor C6.
JU3 1-2* Connects INAP to JU2 and C6 through R2 and R8
2-3 Connects INAP to GND through R2 and R8
JU4
Installed* Connects OUTA to OUTA
Open Connects OUTA to OUTA through capacitor C10. When AC-coupling is desired, remove
the shunt and install capacitor C10.
JU11
Installed* Connects INBM to R11. Also shorts capacitor C15.
Open Connects INBM to R11 through capacitor C15. When AC-coupling is desired, remove the
shunt and install capacitor C15.
JU12
Installed* Connects INBP to JU13 position 1. Also shorts capacitor C16.
Open Connects INBP to JU13 position 1 through capacitor C16. When AC-coupling is desired,
remove the shunt and install capacitor C16.
JU13 1-2* Connects INBP to JU12 and C16 through R12 and R18
2-3 Connects INBP to GND through R12 and R18
JU14
Installed* Connects OUTB to OUTB
Open Connects OUTB to OUTB through capacitor C20. When AC-coupling is desired, remove
the shunt and install capacitor C20.
Evaluates: MAX44251
2
Maxim Integrated
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.
Op-Amp Configurations
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:
OUTA INAP
R5
V (1 ) V
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.
OUTA INAP INAM
V GAIN (V V )= −
where:
R5 R3
GAIN R1 R2
= =
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
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:
CR2 R8 R3 R4
1
f2RRCC
=
π
R2 R8 R3 R4
R3 R2 R8
RRCC
QC (R R )
=
+
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:
CR3 R4 R2 R8
1
f2RRCC
=
π
R3 R4 R2 R8
R4 R2 R8
RRCC
QR (C C )
=
+
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:
VOUT = (IIN + IBIAS) x R4 + VOS
where R4 is installed as a 10kI resistor, IIN is defined
as the input current source applied at the INAM PCB
pad, IBIAS is the input bias current, and VOS 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
Evaluates: MAX44251
Maxim Integrated
3
MAX44251 Evaluation Kit
Figure 1. MAX44251 EV Kit Schematic
Evaluates: MAX44251
4
Maxim Integrated
MAX44251 Evaluation Kit
Figure 2. MAX44251 EV Kit Component Placement Guide—
Component Side
Figure 3. MAX44251 EV Kit PCB Layout—Component Side
Figure 4. MAX44251 EV Kit PCB Layout—Solder Side
1.0”
1.0” 1.0”
Evaluates: MAX44251
Maxim Integrated
5
MAX44251 Evaluation Kit
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 4/12 Initial release —
Evaluates: MAX44251
6Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
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. 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.
© 2012 Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.
