MCP6001T-I/LO データシートの表示（PDF） - Microchip Technology
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MCP6001T-I/LO Datasheet PDF : 24 Pages
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MCP6001/2/4
3.4 Supply Bypass
With this family of operation amplifiers, the power sup-
ply pin (VDD for single supply) should have a local
bypass capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm
for good high frequency performance. It also needs a
bulk capacitor (i.e., 1 µF or larger) within 100 mm to
provide large, slow currents. This bulk capacitor can be
shared with other parts.
3.5 PCB Surface Leakage
In applications where low input bias current is critical,
PCB (printed circuit board) surface leakage effects
need to be considered. Surface leakage is caused by
humidity, dust or other contamination on the board.
Under low humidity conditions, a typical resistance
between nearby traces is 1012Ω. A 5V difference would
cause 5 pA, if current-to-flow; this is greater than the
MCP6001/2/4 family’s bias current at 25°C (1 pA, typ).
The easiest way to reduce surface leakage is to use a
guard ring around sensitive pins (or traces). The guard
ring is biased at the same voltage as the sensitive pin.
An example of this type of layout is shown in
Figure 3-4.
VIN-
VIN+
VSS
Guard Ring
FIGURE 3-4:
Example Guard Ring Layout
for Inverting Gain.
1. Non-inverting Gain and Unity Gain Buffer:
a. Connect the non-inverting pin (VIN+) to the
input with a wire that does not touch the pcb
surface.
b. Connect the guard ring to the inverting input
pin (VIN–). This biases the guard ring to the
common mode input voltage.
2. Inverting and Transimpedance Gain Amplifiers
(convert current to voltage, such as photo detec-
tors):
a. Connect the guard ring to the non-inverting
input pin (VIN+). This biases the guard ring
to the same reference voltage as the op
amp (e.g., VDD/2 or ground).
b. Connect the inverting pin (VIN–) to the input
with a wire that does not touch the PCB
surface.
DS21733D-page 8
3.6 Application Circuits
3.6.1 UNITY GAIN BUFFER
The rail-to-rail input and output capability of the
MCP6001/2/4 op amp is ideal for unity-gain buffer
applications. The low quiescent current and wide band-
width makes the device suitable for a buffer configura-
tion in an instrumentation amplifier circuit, as shown in
Figure 3-5.
VIN1
-
MCP6002
+ 1/2
-
MCP6002
VIN2
+ 1/2
R2
R1
-
MCP6001
+
R2
VOUT
R1
VREF
R1 = 20 kΩ
R2 = 10 kΩ
VOUT
=
(VIN2
–
VIN1)
•
R----1-
R2
+
VREF
FIGURE 3-5:
Instrumentation Amplifier
with Unity Gain Buffer Inputs.
3.6.2 ACTIVE LOW-PASS FILTER
The MCP6001/2/4 op amp’s low input bias current
makes it possible for the designer to use larger resis-
tors and smaller capacitors for active low-pass filter
applications. However, as the resistance increases, the
noise generated also increases. Parasitic capacitances
and the large value resistors could also modify the fre-
quency response. These trade-offs need to be
considered when selecting circuit elements.
It is possible to have a filter cutoff frequency as high as
1/10th of the op amp bandwidth (100 kHz). Figure 3-6
shows a second-order butterworth filter with 100 kHz
cutoff frequency and a gain of +1V/V.
The component values were selected using
Microchip’s FilterLab® software.
100 pF
VIN 14.3 kΩ 53.6 kΩ
33 pF
+
MCP6002
-
VOUT
FIGURE 3-6:
Pass Filter.
Active Second-Order Low-
2003 Microchip Technology Inc.
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