MCP4716 datasheet(52/70 Pages) MICROCHIP

52 / 70 page

MCP47A1

DS25154A-page 52

 2012 Microchip Technology Inc.

8.6

Design Considerations

8.6.1

POWER SUPPLY

CONSIDERATIONS (NOISE)

Inductively-coupled AC transients and digital switching

noise can degrade the input and output signal integrity,

potentially masking the MCP47A1’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 suggested. Particularly harsh environments may

require shielding of critical signals.

The device’s power sources (VDD and VREF) should be

as clean as possible. Any noise induced on the VDD

and VREF signals can affect the DAC performance.

Separate digital and analog ground planes are

recommended.

Typical applications require a bypass capacitor in order

to filter high-frequency noise on the VDD and VREF sig-

nals. The noise can be induced onto the power supply’s

traces or as a result of changes on the DAC output. The

bypass capacitor helps to minimize the effect of these

noise sources on signal integrity. Figure 8-8 illustrates

an appropriate bypass strategy.

In this example, the recommended bypass capacitor

value is 0.1 µF. This capacitor should be placed as

close to the device power pin (VDD) as possible (within

4mm).

Separate digital and analog ground planes are

recommended. In this case, the VSS pin and the ground

pins of the VDD capacitors should be terminated to the

analog ground plane and VDD and VSS should reside

on the analog plane.

Figure 8-9 shows an example of using two bypass

capacitors (a 10 µF tantalum capacitor and a 0.1 µF

ceramic capacitor) in parallel on the VDD line. These

capacitors should be placed as close to the VDD pin as

possible (within 4 mm). If the application circuit has

separate digital and analog power supplies, the VDD

and VSS pins of the device should reside on the analog

plane.

FIGURE 8-8:

Typical Microcontroller

Connections.

FIGURE 8-9:

Example MCP47A1 Circuit.

Note:

Breadboards and wire-wrapped boards

are not recommended.

VDD

VSS

0.1 µF

SCL

SDA

VOUT

VREF

Analog

VDD

SCL

SDA

VSS

VOUT

To MCU

R1 and R2 are I2C pull-up resistors:

R1 and R2:

 - 10 k for f

SCL

= 100 kHz to 400 kHz

C1:

0.1 µF capacitor

Ceramic

C2:

10 µF capacitor

Tantalum

C3:

~ 0.1 µF

Optional to reduce noise

in VOUT pin.

C4:

0.1 µF capacitor

Ceramic

C5:

10 µF capacitor

Tantalum

Optional

Output

VREF

Optional

VREF

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