MCP47DA1 datasheet(47/70 Pages) MICROCHIP

47 / 70 page

 2012 Microchip Technology Inc.

DS25154A-page 47

MCP47A1

8.0

APPLICATIONS EXAMPLES

The MCP47A1 family of devices are general purpose,

single-channel voltage output DACs for various

applications where a precision operation with low

power is needed.

The MCP47A1 devices are rail-to-rail output DACs

designed to operate with a VDD range of 1.8V to 5.5V.

The internal output op amplifier is robust enough to

drive

common,

small-signal

loads

directly,

thus

eliminating the cost and size of external buffers for

most applications.

Applications generally suited for the devices are:

• Set Point or Offset Trimming

• Sensor Calibration

• Portable Instrumentation (Battery Powered)

• Motor Control

Application examples include:

•

DC Set Point or Calibration

•

Decreasing Output Step Size

•

Building a “Window” DAC

•

Selectable Gain and Offset Bipolar Voltage

Output

•

Building Programmable Current Source

•

Serial Interface Communication Times

•

Software I2C Interface Reset Sequence

In the design of a system with the MCP47A1 devices,

the following considerations should be taken into

account:

•

Power Supply Considerations (Noise)

•

PCB Area Requirements

•

Connecting to I2C BUS using Pull-Up

Resistors

8.1

DC Set Point or Calibration

common

application

for

the

devices

digitally-controlled set point and/or calibration of

variable parameters, such as sensor offset or slope.

For example, the MCP47A1 provides 64 output steps

over the voltage reference range. If voltage reference is

1.65V, the LSb size is 1.65V / 64, or ~ 25.78 mV.

Applications that need accurate detection of an input

threshold event often need several sources of error

eliminated. Use of comparators and operational

amplifiers (op amps) with low offset and gain error can

help achieve the desired accuracy, but in many

applications, the input source variation is beyond the

designer’s control. If the entire system can be

calibrated after assembly in a controlled environment

(like factory test), these sources of error are minimized,

if not entirely eliminated. Figure 8-1 illustrates this

example circuit. Equation 8-1 shows a quick estimation

of the wiper value given the desired voltage trip (VTRIP)

point.

FIGURE 8-1:

Set Point or Threshold

Calibration.

EQUATION 8-1:

ESTIMATING THE WIPER

VALUE (N) FROM THE

DESIRED VTRIP

VCC+

VCC–

I2C™

2-wire

VREF

MCP47A1

VDD

VOUT

Comp.

VTRIP

VSENSE

VTRIP = VOUT = (N * VS)

( VTRIP - VREF )

Where: VS = VREF / 64

Note: Calculation does not take into account RFS

and RZS resistors of the DAC’s resistor ladder (see

Section 7.1 for additional information).

N =

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