MCP6292 MICROCHIP [Microchip Technology], MCP6292 Datasheet - Page 14

• Manufacturer Part Number: MCP6292
• Description: 1.0 mA, 10 MHz Rail-to-Rail Op Amp
• Manufacturer: MICROCHIP [Microchip Technology]

MCP6291/1R/2/3/4/5
4.6
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 nearby analog parts.
4.7
An unused op amp in a quad package (MCP6294)
should be configured as shown in
circuits prevent the output from toggling and causing
crosstalk. Circuits A sets the op amp at its minimum
noise gain. The resistor divider produces any desired
reference voltage within the output voltage range of the
op amp; the op amp buffers that reference voltage.
Circuit B uses the minimum number of components
and operates as a comparator, but it may draw more
current.
FIGURE 4-6:
DS21812E-page 14
V
DD
¼ MCP6294 (A)
R
R
V
REF
1
2
Supply Bypass
Unused Op Amps
=
DD
V
V
DD
DD
for single supply) should have a local
⋅
------------------
R
1
R
Unused Op Amps.
+
2
V
R
2
REF
Figure
¼ MCP6294 (B)
V
4-6. These
DD
4.8
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 of current to flow, which is greater than the
MCP6291/1R/2/3/4/5 family’s bias current at 25°C
(1 pA, typical).
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
FIGURE 4-7:
for Inverting Gain.
1.
2.
For
Amplifiers (convert current to voltage, such as
photo detectors):
a.
b.
Non-inverting Gain and Unity-Gain Buffer:
a.
b.
4-7.
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.
Inverting
IN
–). This biases the guard ring to the
V
IN
IN
DD
Guard Ring
Gain
+). This biases the guard ring
Example Guard Ring Layout
–
© 2007 Microchip Technology Inc.
/2 or ground).
12
and
Ω. A 5V difference would
V
IN
+
Transimpedance
IN
–) to the input
IN
V
SS
+) to the