Microchip Technology MCP6N16, Руководство пользователя, Страница: 24 / 36

MCP6N16 Evaluation Board User’s Guide
DS50002365A-page 24
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2015 Microchip Technology Inc.
2.4.3.4 ENABLE FUNCTION
The MCP6N16 instrumentation amplifier features an Enable-pin (EN); since there is no
internal pull-up resistor, the MCP6N16 on the evaluation board is placed into the
Enable state (operational) by an external pull-up resistor (R4). The evaluation board
provides two options for the user to examine the part’s performance in its power-down
state: either in a static mode, by inserting a jumper on J4, or through the CS1 line. If
this line is connected to an external stimulus (CMOS levels), the dynamic performance
can be examined.
2.4.4 External V
REF
Circuit
Included on the evaluation board are various options that deliver an external reference
voltage to the MCP6N16, which can be used to level shift the output signal. Since the
MCP6N16 is configured in a single-supply configuration on the evaluation board, either
the input is biased with an appropriate input DC bias voltage to keep the amplifier within
its specified input range, or the output needs to be level shifted. Refer to the MCP6N16
data sheet for further details.
The MCP1525 (U2) is a precision, low-power voltage reference with an output voltage
of +2.5V. Resistor R23 is a 25-turn potentiometer that is used to provide an adjustment
range of +0.025V to +3.0V at the output of the reference buffer U4. The buffer amplifier
uses the MCP6V11, a zero-drift micro-power operational amplifier that is configured for
a gain of +1.2V/V. To minimize noise the bandwidth of this amplifier stage is limited to
about 8 Hz using capacitor C15, which is placed in parallel with the feedback resistor.
FIGURE 2-8: External Precision Voltage Reference Circuitry.
An alternate method to adjusting the reference voltage manually with R23 is offered
with the Digital Potentiometer device MCP4018. The use of this device will require the
user to connect the MCP4018 I
2
C™ interface to an external controller (e.g. a PIC
microcontroller). Jumper J13 is used to switch between the manual option on the
MCP4018.
3
4
1
U4
MCP6V11T-E/OT
VIN
1
VOUT
2
VSS
3
MCP1525/2.5V
U2
GND
GND GND
1
1
2 3
J13
VREF
0.1uF
C16
10k
R26
0.1uF
C21
GND
0.1uF
C18
GND
200k
R22
VDD
1
VSS
2
SDA
4
SCL
3
5
6 A
W
B
10K
U3
MCP4018
SC-70-6
GND
I2C_DIO
I2C_SCLK
W
W
ADC1
0.1uF
C20
GND
DNP
TP6
TP5
VS+
VS+
2
1
3
10K
R23
1M
R27
100R
R28
1uF
C15
1uF
C17
0R
R32
DNP
0R
R24