MCP4902-ESLASHST datasheet(34/48 Pages) MICROCHIP

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MCP4902/4912/4922

DS22250A-page 34

 2010 Microchip Technology Inc.

6.9

Using Multiplier Mode

The MCP4902/4912/4922 family of devices use exter-

nal reference, and these devices are ideally suited for

use as a multiplier/divider in a signal chain. The

common applications are: (a) Precision programmable

gain/attenuator amplifiers and (b) Motor control

feedback loop. The wide input range (0V – VDD) is in

Unbuffered mode and near rail-to-rail range in Buffered

mode: its bandwidth (> 400 kHz), selectable 1x/2x gain

and low power consumption give maximum flexibility to

meet the application’s needs.

To configure the MCP4902/4912/4922 family of

devices for multiple applications, connect the input sig-

nal to VREF and serially configure the DAC’s input buf-

fer, gain and output value. The DAC’s output can utilize

any of Examples 6-1 to 6-6, depending on the applica-

tion requirements. Example 6-7 is an illustration of how

the DAC can operate in a motor control feedback loop.

If the gain selection bit is configured for 1x mode

(<GA>= 1), the resulting input signal will be attenuated

by D/2n. With the 12-bit DAC (MCP4921 or MCP4922),

if the gain is configured for 2x mode (<GA>= 0), the

codes less than 2048 attenuate the signal, while the

codes greater than 2048 gain the signal.

A DAC provides significantly more gain/attenuation

resolution when compared to typical Programmable

Gain Amplifiers. Adding an op amp to buffer the output,

as illustrated in Examples 6-2 to 6-6, extends the

output range and power to meet the precise needs of

the application.

EXAMPLE 6-7:

MULTIPLIER MODE USING VREF INPUT

VCC+

VCC-

VREF

DAC

VRPM

–

VDD

SPI

VOUT

Rsense

VRPM_SET

MCP4901

MCP4911

MCP4921

(a) Single Output DAC:

(b) Dual Output DAC:

MCP4902

MCP4912

MCP4922

VOUT

VREF G

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