MCP6283-E/SL Microchip Technology, MCP6283-E/SL Datasheet - Page 12

• Manufacturer Part Number: MCP6283-E/SL
• Description: 450 uA, 5 MHz Rail-to-Rail Op Amp
• Manufacturer: Microchip Technology

MCP6281/2/3/4/5
3.6
With this family of operational amplifiers, the power
supply pin (V
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.
3.7
In applications where low input bias current is critical,
printed circuit board (PCB) 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 10
cause 5 pA, if current-to-flow, which is greater than the
MCP6281/2/3/4/5 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 3-7.
FIGURE 3-7:
for Inverting Gain.
1.
2.
DS21811C-page 12
For Inverting (Figure 3-7) and Transimpedance
Amplifiers (convert current to voltage, such as
photo detectors):
a.
b.
Non-inverting Gain and Unity-Gain Buffer:
a.
b.
Supply Bypass
PCB Surface Leakage
Connect the guard ring to the non-inverting
input pin (V
to the same reference voltage as the op
amp (e.g., V
Connect the inverting pin (V
with a wire that does not touch the PCB
surface.
Connect the non-inverting pin (V
input with a wire that does not touch the
PCB surface.
Connect the guard ring to the inverting input
pin (V
common mode input voltage.
DD
IN
for single-supply) should have a local
–). This biases the guard ring to the
V
IN
IN
DD
Guard Ring
+). This biases the guard ring
Example Guard Ring Layout
–
/2 or ground).
12
. A 5V difference would
V
IN
+
IN
–) to the input
IN
V
SS
+) to the
3.8
3.8.1
The MCP6281/2/3/4/5 op amps can be used in active-
filter applications. Figure 3-8 shows a second-order
Sallen-Key highpass filter with a gain of 1. The output
bias voltage is set by the V
be changed to any voltage within the output voltage
range.
FIGURE 3-8:
This filter, and others, can be designed using
Microchip’s FilterLab
our web site (www.microchip.com).
3.8.2
Analog integrators are used in filters, control loops and
measurement circuits. Figure 3-9 shows the most
common implementation, the inverting Miller integrator.
The non-inverting input is at V
properly biases up. The switch (SW) is used to zero the
output in some applications. Other applications use a
feedback loop to keep the output within its linear range
of operation.
FIGURE 3-9:
V
IN
V
IN
Application Circuits
C
V
SALLEN-KEY HIGHPASS FILTER
1
INVERTING MILLER INTEGRATOR
DD
R
/2
V
R
DD
C
R
1
2
/2
2
®
MCP6281
+
Sallen-Key Highpass Filter.
–
Miller Integrator.
software, which is available on
 2004 Microchip Technology Inc.
SW
C
DD
MCP6281
+
–
DD
/2 reference, which can
/2 so that the op amp
V
V
OUT
IN
V
OUT
=
sRC
V
1
OUT