Datasheet

JUMPER SHUNT POSITION DESCRIPTION
JU1
Installed* Connects the IN- PCB pad to GND.
Not installed Isolates the IN- PCB pad from GND.
JU2
1-2*
Connects SHDN to VDD (normal operation).
2-3
Connects SHDN to GND (shutdown).
_________________________________________________________________ Maxim Integrated Products 2
MAX44265 Evaluation Kit
Evaluates: MAX44265
Quick Start
Required Equipment
• MAX44265 EV kit
• +5V, 10mA DC power supply (PS1)
• Precision voltage source
• Digital multimeter (DMM)
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 positions, as
shown in Table 1.
2) Connect the positive terminal of the +5V supply to the
VDD PCB pad and the negative terminal to the GND
PCB pad closest to VDD.
3) Connect the positive terminal of the precision voltage
source to the IN+ PCB pad. Connect the negative
terminal of the precision voltage source to GND (GND
or IN- PCB pads).
4) Connect the DMM to monitor the voltage on the OUT
PCB pad. With the 10kI feedback resistor (R5) and
1kI series resistor (R1), the gain is +11 (noninverting
configuration).
5) Turn on the +5V power supply.
6) Apply 100mV from the precision voltage source.
Observe the output at OUT on the DMM. OUT should
read approximately +1.1V.
7) Apply 400mV from the precision voltage source. OUT
should read approximately +4.4V.
Detailed Description of Hardware
The MAX44265 EV kit provides a proven layout for the
MAX44265 low-power, MOS-input op amp. The device is
a single-supply op amp that is ideal for buffering sensor
signals. The Sallen-Key topology is easily accomplished
by changing and removing some components. The
Sallen-Key topology is ideal for buffering and filtering
sensor signals.
Op-Amp Configurations
The device is a single-supply op amp that is ideal for
differential sensing, noninverting amplification, buffering,
and filtering. A few common configurations are detailed
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/R1. The EV kit comes
preconfigured for a gain of +11. For a voltage applied to
the IN+ PCB pad, the output voltage for the noninverting
configuration is given by the equation below:
OUT IN OS
R5
V (1 )(V V )
R1
+
= + +
where V
OS
= Input-referred offset voltage.
Differential Amplifier
To configure the EV kit as a differential amplifier, replace R1,
R2, R
C3
, and R5 with appropriate resistors. When R1 = R2
and R
C3
= R5, the CMRR of the differential amplifier is deter-
mined by the matching of resistor ratios R1/R2 and R
C3
/R5:
OUT IN IN OS
R5
V Gain(V V ) (1 )V
R1
+ −
= − + +
where:
C3
R
R5
Gain
R1 R2
= =
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. The signal is
noninverting and applied to IN+. The filter component
pads are R2, R3, R4, and R8, where some have to be
populated with resistors and others with capacitors.
Table 1. Jumper Descriptions (JU1, JU2)
*Default position.