MCP6273-E/SL Microchip Technology, MCP6273-E/SL Datasheet - Page 12

• Manufacturer Part Number: MCP6273-E/SL
• Description: 170 uA, 2 MHz Rail-to-Rail Op Amp
• Manufacturer: Microchip Technology

MCP6271/2/3/4/5
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. This is greater than the
MCP6271/2/3/4/5 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 illustrated in
Figure 3-7.
FIGURE 3-7:
for Inverting Gain.
1.
2.
DS21810C-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 MCP6271/2/3/4/5 family of amplifiers can be used
in applications such as an Active Full-Wave Rectifier or
an Absolute Value circuit, as shown in Figure 3-8. The
amplifier and feedback loops in this active voltage
rectifier circuit eliminate the diode drop problem that
exists in a passive voltage rectifier. This circuit behaves
as a follower (the output follows the input) as long as
the input signal is more positive than the reference
voltage. If the input signal is more negative than the
reference voltage, however, the circuit behaves as an
inverting amplifier. Therefore, the output voltage will
always be above the reference voltage, regardless of
the input signal.
FIGURE 3-8:
V
V
V
R
REF
REF
IN
3
Application Circuits
Input
MCP6272
–
+
ACTIVE FULL-WAVE RECTIFIER
time
R
R
D
1
A
4
2
R
5
Active Full-wave Rectifier.
 2004 Microchip Technology Inc.
D
1
V
R
R
REF
V
MCP6272
–
+
1
5
REF
=
=
R
Output
R
R
----- -
R
2
2
1
2
B
=
time
R
3
=
V
R
OUT
4