MCP4021 datasheet(41/64 Pages) MICROCHIP

41 / 64 page

DS21945E-page 41

MCP4021/2/3/4

5.3

CS High Voltage

Depending on the requirements of the system, the use

of high voltage (VIHH) on the CS pin, may or may not be

required during system operation. Table 5-2 shows

possible system applications, and whether a high

voltage (VIHH) is required on the system.

The MCP402X supports six high-voltage commands

(the CS input voltage must meet the VIHH

specification).

TABLE 5-2:

HIGH-VOLTAGE

APPLICATIONS

5.3.1

TECHNIQUES TO FORCE THE CS

PIN TO VIHH

The circuit in Figure 5-12 shows a method using the

TC1240A doubling charge pump. When the SHDN pin

is high, the TC1240A is off, and the level on the CS 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 CS

pin to go higher than the voltage such that the PIC

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

FIGURE 5-12:

Using the TC1240A to

generate the VIHH voltage.

The circuit in Figure 5-13 shows the method used on

the MCP402X Non-volatile Digital Potentiometer

Evaluation Board. This method requires that the

system voltage be approximately 5V. This ensures that

when the PIC10F206 enters a brown-out condition,

there is an insufficent voltage level on the CS pin to

change the stored value of the wiper. The MCP402X

Non-volatile Digital Potentiometer Evaluation 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 impedence). The output state of the GP0 pin

will determine the voltage on the CS 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 5-13:

MCP402X Non-volatile

Digital Potentiometer Evaluation Board

(MCP402XEV) implementation to generate the

VIHH voltage.

System Operation

High

Voltage

Production calibration only - system

should not update wiper setting

From

Calibration

Unit

WiperLock™ Technogy disabled during

system operation

Not

Required

Wiper setting can be updated and

“locked” during system operation

Required

PIC® MCU

MCP402X

IO1

IO2

TC1240A

VIN

SHDN

C+

C-

VOUT

PIC10F206

MCP402X

GP0

GP2

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