MCP4921 datasheet(34/50 Pages) MICROCHIP

34 / 50 page

MCP4901/4911/4921

DS22248A-page 34

 2010 Microchip Technology Inc.

6.9

Using Multiplier Mode

The MCP4901/4911/4921 and MCP4902/MCP4912/

MCP4922 family devices use external reference, and

these devices are ideally suited for use as a multiplier/

divider in a signal chain. Common applications are: (a)

precision programmable gain/attenuator amplifiers and

(b) motor control feedback loops. 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 device for multiplier applications,

connect the input signal to VREF and serially configure

the DAC’s input buffer, gain and output value. The

DAC’s output can utilize any of the examples from 6-1

to 6-6, depending on the application 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), codes

less than 2048 attenuate the signal, while 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 through 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

OUT

REF

------

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