MCP6546T-I/P Microchip Technology, MCP6546T-I/P Datasheet - Page 14

• Manufacturer Part Number: MCP6546T-I/P
• Description: Push-Pull Output Sub-Microamp Comparator
• Manufacturer: Microchip Technology

MCP6546/7/8/9
FIGURE 3-6:
strategies to reduce surface leakage effects.
3.8.2
Separate digital from analog, and low speed from high
speed. This helps prevent crosstalk.
Keep sensitive traces short and straight. Separate
them from interfering components and traces. This is
especially important for high frequency (low rise time)
signals.
Use a 0.1 µF supply bypass capacitor within 0.1”
(2.5 mm) of the V
ground plane.
3.8.3
The input pins of the family of op amps are high imped-
ance, which allows noise injection. This noise can be
capacitively or magnetically coupled. In either case,
using a ground plane helps reduce noise injection.
When noise is coupled capacitively, ground plane
reduces the coupling capacitance, and provides shunt
capacitance to ground for high frequency signals;
Figure 3-7 shows the equivalent circuit. The coupled
current, I
victim trace when the trace to ground plane capaci-
tance (C
is small. Increasing the distance between traces, and
using wider traces, also helps.
DS21714A-page 14
.
Figure 3-6A
Figure 3-6B
SH
COMPONENT PLACEMENT
SIGNAL COUPLING
M
, produces a lower voltage (V
2
V
) is large, and the terminating resistor (R
REF
Two possible guard ring connection
DD
pin. It must connect directly to the
MCP654X
MCP654X
V
V
Trace 2
DD
DD
) on the
T
2
)
FIGURE 3-7:
coupling between traces on a PC board (with ground
plane).
When noise is coupled magnetically, ground plane
reduces the mutual inductance between traces. This
occurs because the ground return current at high fre-
quencies will follow a path directly beneath the signal
trace. Increasing the separation between traces makes
a significant difference. Changing the direction of one
of the traces can also reduce magnetic coupling.
If these techniques are not enough, it may help to place
guard traces next to the victim trace. They should be on
both sides of the victim trace, and as close as possible.
Connect the guard traces to ground plane at both ends,
and in the middle for long traces.
3.9
3.9.1
Some applications require higher DC precision. An
easy way to solve this problem is to gain up the input
signal before it reaches the comparator. Figure 3-8
shows an example of this approach.
FIGURE 3-8:
.
V
V
IN
V
T
REF
RACE
Typical Applications
PRECISE COMPARATOR
1
R
C
1
SH1
Equivalent
Precise Inverting comparator.
MCP6XXX
R
V
2
V
DD
C
REF
C
M
2002 Microchip Technology Inc.
SH2
I
circuit
M
MCP654X
V
V
for
T
DD
RACE
capacitive
2
R
V
T2
OUT