MCP6L71 Microchip Technology Inc., MCP6L71 Datasheet - Page 14

• Manufacturer Part Number: MCP6L71
• Description: 2 Mhz, 150 ?a Op Amps
• Manufacturer: Microchip Technology Inc.

MCP6L71/1R/2/4
4.4
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.
4.5
An unused op amp in a quad package (MCP6L74)
should be configured as shown in
circuits prevent the output from toggling and causing
crosstalk. In Circuit A, R
within its output voltage range (V
buffers this voltage, which can be used elsewhere in
the circuit. Circuit B uses the minimum number of
components and operates as a comparator.
FIGURE 4-3:
4.6
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. This is greater than the
MCP6L71/1R/2/4 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.
Figure 4-4
DS22145A-page 14
¼ MCP6L74 (A)
V
V
DD
REF
R
R
1
2
Supply Bypass
Unused Amplifiers
PCB Surface Leakage
=
shows an example of this type of layout.
V
DD
DD
V
⋅
for single supply) should have a local
DD
------------------
R
1
R
+
2
R
Unused Op Amps.
2
1
and R
12
V
REF
Ω. A 5V difference would
OH
2
¼ MCP6L74 (B)
, V
produce a voltage
Figure
OL
V
). The op amp
DD
4-3. These
FIGURE 4-4:
Layout.
1.
2.
4.7
4.7.1
An inverting integrator is shown in
circuit provides an output voltage that is proportional to
the negative time-integral of the input. The additional
resistor R
To minimize the integrator’s error for slow signals, the
value of R
FIGURE 4-5:
For
Amplifiers (convert current to voltage, such as
photo detectors):
a)
b)
Non-inverting Gain and Unity Gain Buffer:
a)
b)
Guard Ring
V
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 guard ring to the inverting input
pin (V
common mode input voltage.
Connect the non-inverting pin (V
input with a wire that does not touch the
PCB surface.
Application Circuits
IN
2
2
Inverting
limits DC gain and controls output clipping.
should be much larger than the value of R
INVERTING INTEGRATOR
IN
R
–). This biases the guard ring to the
1
V
OUT
IN
V
DD
Gain
+). This biases the guard ring
Example Guard Ring
Inverting Integrator.
IN
© 2009 Microchip Technology Inc.
/2 or ground).
–
=
+
_
MCP6L71
R
–
------------ -
R
2
and
R
C
V
»
1
1
2
C
1
IN
R
1
1
+
∫
Transimpedance
0
t
IN
V
Figure
–) to the input
IN
t d
V
IN
OUT
+) to the
4-5. The
1
.