MCP6542 Microchip Technology Inc., MCP6542 Datasheet - Page 17

• Manufacturer Part Number: MCP6542
• Description: Push-pull Output Sub-microamp Comparators
• Manufacturer: Microchip Technology Inc.

4.8
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 10
cause 5 pA of current to flow. This is greater than the
MCP6541/1R/1U/2/3/4 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
FIGURE 4-9:
for Inverting Circuit.
1.
2.
© 2007 Microchip Technology Inc.
Inverting Configuration (Figures
a.
b.
Non-inverting Configuration
a.
b.
4-9.
PCB Surface Leakage
Connect the guard ring to the non-inverting
input pin (V
to the same reference voltage as the
comparator (e.g., V
Connect the inverting pin (V
pad without touching the guard ring.
Connect the non-inverting pin (V
input pad without touching the guard ring.
Connect the guard ring to the inverting input
pin (V
IN
–).
V
IN
IN
Guard Ring
+). This biases the guard ring
Example Guard Ring Layout
-
12
DD
Ω. A 5V difference would
/2 or ground).
V
(Figure
IN
+
IN
4-6
–) to the input
4-4):
and 4-9):
IN
V
SS
+) to the
MCP6541/1R/1U/2/3/4
4.9
An unused amplifier in a quad package (MCP6544)
should be configured as shown in
circuit prevents the output from toggling and causing
crosstalk. It uses the minimum number of components
and draws minimal current (see
Figure
FIGURE 4-10:
2-18).
Unused Comparators
¼ MCP6544
–
+
Unused Comparators.
V
DD
DS21696F-page 17
Figure
Figure 2-15
4-10. This
and