MCP6546-ILT Microchip Technology, MCP6546-ILT Datasheet - Page 14

• Manufacturer Part Number: MCP6546-ILT
• Description: Open-Drain Output Sub-Microamp Comparators
• Manufacturer: Microchip Technology

MCP6546/7/8/9
FIGURE 3-5:
layout.
Circuit schematics for different guard ring implementa-
tions are shown in Figure 3-6. Figure 3-6A biases the
guard ring to the input common mode voltage.
Figure 3-6B biases the guard ring to a reference volt-
age (V
on the node that is the most constant.
FIGURE 3-6:
connection 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.
DS21714B-page 14
.
.
Figure 3-6A
Figure 3-6B
REF
, which can be ground). Place the guard ring
V
REF
COMPONENT PLACEMENT
DD
IN-
pin. It must connect directly to the
Guard Ring
Example of guard ring
Two possible guard ring
IN+
MCP654X
MCP654X
V
V
DD
DD
V
SS
3.8.3
The input pins of the MCP6546/7/8/9 family of compar-
ators are high-impedance, 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, a 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.
FIGURE 3-7:
capacitive 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 be as close as possi-
ble. Connect the guard traces to ground plane at both
ends, and in the middle for long traces.
.
V
T
RACE
SH2
M
1
) produces a lower voltage (V
C
SIGNAL COUPLING
) is large, and the terminating resistor (R
SH1
Equivalent circuit for
C
C
M
2002 Microchip Technology Inc.
SH2
I
M
V
T
RACE
Trace 2
2
) on the
R
T2
T
2
)