MCP6546-I/LT Microchip Technology, MCP6546-I/LT Datasheet - Page 14

• Manufacturer Part Number: MCP6546-I/LT
• Description: Comparator
• Manufacturer: Microchip Technology

MCP6546/7/8/9
3.7
In order to maximize battery life in portable
applications, use large resistors and small capacitive
loads. Also, avoid toggling the output more than
necessary and do not use chip select (CS) to conserve
power for short periods of time. Capacitive loads will
draw additional power at start-up.
3.8
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
would cause 5 pA. If current-to-flow, this is greater
than the MCP6546/7/8/9 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 3-6.
FIGURE 3-6:
for Inverting Circuit.
1.
DS21714C-page 14
Inverting Configuration (Figures 3-3 and 3-6):
a.
b.
Battery Life
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.
V
IN
IN
Guard Ring
+). This biases the guard ring
Example Guard Ring Layout
-
DD
/2 or ground).
V
12
IN
+
. A 5V difference
IN
–) to the input
V
SS
3.9
3.9.1
Some applications require higher DC precision. An
easy way to solve this problem is to use an amplifier
(such as the MCP6041) to gain-up the input signal
before it reaches the comparator. Figure 3-7 shows an
example of this approach.
FIGURE 3-7:
Comparator.
3.9.2
Figure 3-8 shows one approach to designing a
windowed comparator. The wired-OR connection
produces a high output (logic 1) when the input voltage
is between V
FIGURE 3-8:
V
V
IN
REF
V
V
V
RT
IN
RB
Typical Applications
R
1
PRECISE COMPARATOR
WINDOWED COMPARATOR
RB
MCP6041
and V
V
R
DD
V
2
RT
REF
Precise Inverting
Windowed comparator.
1/2
MCP6547
(where V
2003 Microchip Technology Inc.
1/2
MCP6547
MCP6546
RT
V
V
PU
DD
> V
R
PU
RB
V
).
PU
V
OUT
R
PU
V
OUT