MCP47DA1 datasheet(51/76 Pages) MICROCHIP

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 2012-2013 Microchip Technology Inc.

DS25118D-page 51

MCP47DA1

8.0

APPLICATIONS EXAMPLES

The MCP47DA1 family of devices are general purpose,

single-channel voltage output DACs for various

applications where a precision operation with low

power is needed.

The MCP47DA1 devices are rail-to-rail output DACs

designed to operate with a VDD range of 2.7V 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 MCP47DA1 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

A common application for the devices is a

digitally-controlled set point and/or calibration of

variable parameters, such as sensor offset or slope.

For example, the MCP47DA1 provides 64 output steps

over 1/3 of the voltage reference range. If voltage

reference is 1.65V, the LSb size is 1.65V / 192, or ~

8.6 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

MCP47DA1

VDD

VOUT

Comp.

VTRIP

VSENSE

VTRIP = VOUT = (1/3) * VREF + (N * VS)

( VTRIP - ( (1/3) * VREF ) )

Where: VS = VREF / 192

Note:

Calculation does not take into account

RFS and RZS resistors of the DAC’s

resistor ladder (see Section 7.1 for

N =

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