MCP4641 datasheet(71/102 Pages) MICROCHIP

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 2008-2013 Microchip Technology Inc.

DS22107B-page 71

MCP454X/456X/464X/466X

8.5

Design Considerations

In the design of a system with the MCP4XXX devices,

the following considerations should be taken into

account:

• Power Supply Considerations

• Layout Considerations

8.5.1

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.

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.

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.

FIGURE 8-6:

Typical Microcontroller

Connections.

8.5.2

LAYOUT CONSIDERATIONS

Several layout considerations may be applicable to

your application. These may include:

• Noise

• Footprint Compatibility

• PCB Area Requirements

8.5.2.1

Noise

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

boards

utilizing a low-inductance ground plane,

isolated inputs, isolated outputs and proper decoupling

are critical to achieving the performance that the silicon

capable

providing.

Particularly

harsh

environments may require shielding of critical signals.

If low noise is desired, breadboards and wire-wrapped

boards are not recommended.

8.5.2.2

Footprint Compatibility

The specification of the MCP4XXX pinouts was done to

allow systems to be designed to easily support the use

of either the dual (MCP46XX) or quad (MCP44XX)

device.

Figure 8-7 shows how the dual pinout devices fit on the

quad device footprint. For the Rheostat devices, the

dual device is in the MSOP package, so the footprints

would need to be offset from each other.

FIGURE 8-7:

Quad Pinout (TSSOP

Package) vs. Dual Pinout.

VDD

VSS

0.1 µF

SCL

SDA

RESET

VDD

MCP44X1 Quad Potentiometers

TSSOP

P0W

P0B

P0A

P1A

P1W

P1B

VSS

HVC/A0

SDA

SCL

MCP44X2 Quad Rheostat

P0B

P0W

VDD

TSSOP

P2W

P1W

P2B

P3B

P3W

P1B

VSS

HVC/A0

SDA

SCL

P3B

P3W

P3A

P2W

P2A

P2B

MCP42X1 Pinout (1)

MCP42X2 Pinout

Note 1: Pin 15 (RESET) is the Address A2 (A2)

pin on the MCP46x1 device.

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