MCP413X/415X/423X/425X
8.4.2
LAYOUT CONSIDERATIONS
8.4
Design Considerations
Inductively-coupled AC transients and digital switching
noise can degrade the input and output signal integrity,
potentially masking the MCP4XXX’s performance.
Careful board layout minimizes these effects and
increases the Signal-to-Noise Ratio (SNR). Multi-layer
In the design of a system with the MCP4XXX devices,
the following considerations should be taken into
account:
• Power Supply Considerations
• Layout Considerations
boards utilizing
a low-inductance ground plane,
isolated inputs, isolated outputs and proper decoupling
are critical to achieving the performance that the silicon
is capable of providing. Particularly harsh
environments may require shielding of critical signals.
8.4.1
POWER SUPPLY
CONSIDERATIONS
The typical application will require a bypass capacitor
in order to filter high-frequency noise, which can be
induced onto the power supply's traces. The bypass
capacitor helps to minimize the effect of these noise
sources on signal integrity. Figure 8-6 illustrates an
appropriate bypass strategy.
If low noise is desired, breadboards and wire-wrapped
boards are not recommended.
8.4.3
RESISTOR TEMPCO
Characterization curves of the resistor temperature
coefficient (Tempco) are shown in Figure 2-11,
Figure 2-24, Figure 2-36, and Figure 2-48.
In this example, the recommended bypass capacitor
value is 0.1 µF. This capacitor should be placed as
close (within 4 mm) to the device power pin (VDD) as
possible.
These curves show that the resistor network is
designed to correct for the change in resistance as
temperature increases. This technique reduces the
end to end change is RAB resistance.
The power source supplying these devices should be
as clean as possible. If the application circuit has
separate digital and analog power supplies, VDD and
VSS should reside on the analog plane.
8.4.4
HIGH VOLTAGE TOLERANT PINS
High Voltage support (VIHH) on the Serial Interface pins
supports two features. These are:
VDD
• In-Circuit Accommodation of split rail applications
and power supply sync issues
0.1 µF
• Compatability with systems that also support
MCP414X/416X /424X/426X devices
VDD
0.1 µF
A
W
U/D
CS
B
VSS
VSS
FIGURE 8-6:
Typical Microcontroller
Connections.
© 2008 Microchip Technology Inc.
DS22060B-page 61
MICROCHIP [ MICROCHIP ]
