LMP7721MAEVAL National Semiconductor, LMP7721MAEVAL Datasheet - Page 2

• Manufacturer Part Number: LMP7721MAEVAL
• Description: BOARD EVALUATION FOR LMP7721
• Manufacturer: National Semiconductor
• Series: LMP®, PowerWise®r

Specifications of LMP7721MAEVAL

• Channels Per Ic: 1 - Single
• Amplifier Type: General Purpose
• Output Type: Single-Ended
• Slew Rate: 12.8 V/µs
• Current - Output / Channel: 60mA
• Operating Temperature: -40°C ~ 125°C
• Current - Supply (main Ic): 1.3mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5.5 V, ±0.9 V ~ 2.75 V
• Board Type: Fully Populated
• Utilized Ic / Part: LMP7721
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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The evaluation board is design to be compatible with the 1 fA
input bias current of the LMP7721 by providing a guarded
area around the input puts of the amplifier. The input guard
creates an equal potential zone around the input pins that
prevents leakage currents from other parts of the PCB from
reaching the input pins and causing an error current. A de-
scription of the board’s features follows:
Power Supply Connections
J3, J4 and J5 are the power supply connections. The power
supply can be a single supply with a range 1.8 to 5.5 volts.
Also, a split supply voltage can be used with the with the con-
dition that 1.8 volts
gether and is the ground connection. The positive supply
voltage connection is J5.
connected to J3. The positive supply voltage is connected to
J5 and the ground (or common) connection of the supplies is
connected to J4.
Reference Voltage Connection
(V
The LMP7721 can be configured as an inverting amplifier or
a non-inverting amplifier. In each case, it may be required to
provide a level shift voltage to keep the output voltage within
a specified range and is accomplished by using the V
nection. Jumper JP3 is used to connect the V
inverting input of U1 when U1 is used in an inverting amplifier
configuration. Jumper JP6 is used to connect the V
inverting input of U1 when U1 is used in a non-inverting am-
plifier configuration.
Components R
and R
These components are shown, as resistors on the schematic
are not mounted on the board. This evaluation board uses pin
sockets at the location of these components to give the user
the freedom to configure the LMP7721 amplifier to best fit the
application being considered.
Jumper Functions
JP1 JP1 is used to connect the signal terminal of the triax
REF
For single supply operation, J3 and J4 are connected to-
For split-supply operation, the negative supply voltage is
connector (J2) to the inverting input or the non-inverting
input of U1, the LMP7721 amplifier.
)
7
≤
V
+
-(V
1
, R
−
)
≤
2
5.5 volts.
, R
3
, R
4
, R
REF
5
to the non-
, R
REF
REF
to the
6
con-
2
JP2 JP2 is used to connect the non-inverting input of U1 to
JP3 JP3 is used to connect the non-inverting terminal of the
JP4 JP4 is used to connect the guard and guard driver to the
JP5 JP5 is used to connect the guard and guard driver to the
JP6 JP6 is used to connect the inverting terminal of the
Input and output connectors
J1 J1 is a BNC connect and is the output of the LMP7721
J2 J2 is a Triax connector and is used to connect a signal
Example Applications
Non-inverting amplifier with a gain of two:
In this example a sensor such as a pH electrode is the signal
source and the LMP7721 is being used to buffer and amplify
the signal. The output of a pH electrode, at 25°C ranges from
about +415 mV to −415 mV as the pH ranges from 0 to 14.
The output impedance of a pH electrode is extremely high,
greater then 5 to 10 MΩ, so the LMP7721 is an excellent am-
plifier to buffer the output of a pH electrode.
For this application, a ±2.5 volt supply voltage will be used.
The following schematic shows the placement of the jumpers
and components.
amplifier
source to the input of the LMP7721. This component is
not mounted on the board. A Triax connector is similar to
a BNC connector but includes a shield between the cen-
tral conductor and the outer shield and is referred to as a
guard. A guard driver drives the guard to the same voltage
as the center conductor, which minimizes any leakage
currents in the connector or in the triax cable connected
to it.
ground.
LMP7721 to the V
can be direct by using a wire jumper in the position of
R
positions of R
inverting terminal of the LMP7721 when it is the low
impedance node. This is the case when the LMP7721
is used as a non-inverting amplifier.
non-inverting terminal of the LMP7721 when it is the low
impedance node. This is the case when the LMP7721
is used as an inverting amplifier.
LMP7721 to the V
used when U1 is used as a non-inverting amplifier.
5
, or through a voltage divider by using resistors in the
5
and R
REF
REF
6
.
voltage. The connection to V
voltage or to ground. These is
REF