MCP4441 datasheet(73/100 Pages) MICROCHIP

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DS22265A-page 73

MCP444X/446X

8.0

APPLICATIONS EXAMPLES

Nonvolatile digital potentiometers have a multitude of

practical uses in modern electronic circuits. The most

popular uses include precision calibration of set point

thresholds, sensor trimming, LCD bias trimming, audio

attenuation, adjustable power supplies, motor control

overcurrent trip setting, adjustable gain amplifiers and

offset trimming. The MCP44XX devices can be used to

replace the common mechanical trim pot in

applications where the operating and terminal voltages

are within CMOS process limitations (VDD = 2.7V to

5.5V).

8.1

Techniques to Force the HVC/A0

Pin to VIHH

The circuit in Figure 8-1 shows a method using the

TC1240A doubling charge pump. When the SHDN pin

is high, the TC1240A is off, and the level on the HVC/

A0 pin is controlled by the PIC® microcontrollers

(MCUs) IO2 pin.

When the SHDN pin is low, the TC1240A is on and the

VOUT voltage is 2 * VDD. The resistor R1 allows the

HVC/A0 pin to go higher than the voltage such that the

PIC MCU’s IO2 pin “clamps” at approximately VDD.

FIGURE 8-1:

Using the TC1240A to

Generate the VIHH Voltage.

The circuit in Figure 8-2 shows the method used on the

MCP402X Nonvolatile Digital Potentiometer Evaluation

Board (Part Number: MCP402XEV). This method

requires that the system voltage be approximately 5V.

This ensures that when the PIC10F206 enters a brown-

out condition, there is an insufficient voltage level on

the HVC/A0 pin to change the stored value of the wiper.

The MCP402X Nonvolatile Digital Potentiometer Eval-

uation Board User’s Guide (DS51546) contains a

complete schematic.

GP0 is a general purpose I/O pin, while GP2 can either

be a general purpose I/O pin or it can output the internal

clock.

For the serial commands, configure the GP2 pin as an

input (high impedance). The output state of the GP0 pin

will determine the voltage on the HVC/A0 pin (VIL or

VIH).

For high-voltage serial commands, force the GP0

output pin to output a high level (VOH) and configure the

GP2 pin to output the internal clock. This will form a

charge pump and increase the voltage on the CS pin

(when the system voltage is approximately 5V).

FIGURE 8-2:

MCP4XXX Nonvolatile

Digital Potentiometer Evaluation Board

(MCP402XEV) implementation to generate the

VIHH voltage.

HVC/A0

PIC MCU

MCP4XXX

IO1

IO2

TC1240A

VIN

SHDN

C+

C-

VOUT

HVC/A0

PIC10F206

MCP4XXX

GP0

GP2

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