MCP4716 datasheet(65/86 Pages) MICROCHIP

65 / 86 page

DS22272A-page 65

MCP4706/4716/4726

8.3

Application Examples

The MCP47X6 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. The user can use gain of 1 or 2 of

the output op amplifier by setting the configuration

reference or use external reference. Various user

options and easy-to-use features make the devices

suitable for various modern DAC applications.

Application examples include:

• Decreasing Output Step Size

• Building a “Window” DAC

• Bipolar Operation

• Selectable Gain and Offset Bipolar Voltage Output

• Designing a Double-Precision DAC

• Building Programmable Current Source

• Serial Interface Communication Times

• Software I2C Interface Reset Sequence

• Power Supply Considerations

• Layout Considerations

8.3.1

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 MCP4726 provides 4096 output

steps. If voltage reference is 4.096V, the LSb size is

1 mV. If a smaller output step size is desired, a lower

external voltage reference is needed.

8.3.1.1

Decreasing Output Step Size

If the application is calibrating the bias voltage of a

diode or transistor, a bias voltage range of 0.8V may be

desired with about 200 µV resolution per step. Two

common methods to achieve small step size are using

lower VREF pin voltage or using a voltage divider on the

DAC’s output.

Using an external voltage reference (VREF) is an

option, if the external reference is available with the

desired output voltage range. However, occasionally,

when using a low-voltage reference voltage, the noise

floor causes a SNR error that is intolerable. Using a

voltage divider method is another option, and provides

some advantages when external voltage reference

needs to be very low, or when the desired output

voltage is not available. In this case, a larger value

reference voltage is used, while two resistors scale the

output range down to the precise desired level.

Figure 8-3 illustrates this concept. A bypass capacitor

on the output of the voltage divider plays a critical

function in attenuating the output noise of the DAC and

the induced noise from the environment.

FIGURE 8-3:

Example Circuit Of Set Point

or Threshold Calibration.

EQUATION 8-1:

VOUT AND VTRIP

CALCULATIONS

VCC+

VCC–

VOUT

I2C™

2-wire

VREF

Optional

MCP47X6

VDD

RSENSE

Comp.

VDD

VTRIP

trip

OUT

--------------------

⎝⎠

⎜⎟

⎛⎞

VOUT = VREF • G •

DAC Register Value

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