MCP433X datasheet(63/88 Pages) MICROCHIP

63 / 88 page

 2010 Microchip Technology Inc.

DS22242A-page 63

MCP433X/435X

8.0

APPLICATIONS EXAMPLES

Digital potentiometers have a multitude of practical

uses in modern electronic circuits. The most popular

uses include precision calibration of set point thresh-

olds, sensor trimming, LCD bias trimming, audio atten-

uation, adjustable power supplies, motor control

overcurrent trip setting, adjustable gain amplifiers and

offset trimming. The MCP433X/435X 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

Split Rail Applications

All inputs that would be used to interface to a host

controller support high voltage on their input pin. This

allows the MCP43XX device to be used in split power

rail applications.

An example of this is a battery application where the

PIC® MCU is directly powered by the battery supply

(4.8V) and the MCP43XX device is powered by the

3.3V regulated voltage.

For SPI applications, these inputs are:

•CS

•SCK

• SDI (or SDI/SDO)

• RESET

Figure 8-1 through Figure 8-2 show three example split

rail systems. In this system, the MCP43XX interface

input signals need to be able to support the PIC MCU

output high voltage (VOH).

In Example #1 (Figure 8-1), the MCP43XX interface

input signals need to be able to support the PIC MCU

output high voltage (VOH). If the split rail voltage delta

becomes too large, then the customer may be required

to do some level shifting due to MCP43XX VOH levels

related to host controller VIH levels.

In Example #2 (Figure 8-2), the MCP43XX interface

input signals need to be able to support the lower

voltage of the PIC MCU output high voltage level (VOH).

Table 8-1 shows an example PIC microcontroller I/O

voltage

specifications

and

the

MCP43XX

specifications. So this PIC MCU operating at 3.3V will

drive a VOH at 2.64V, and for the MCP43XX operating

at 5.5V, the VIH is 2.47V. Therefore, the interface

signals meet specifications.

FIGURE 8-1:

Example Split Rail

System 1.

FIGURE 8-2:

Example Split Rail

System 2.

TABLE 8-1:

VOH – VIH COMPARISONS

PIC® MCU (1)

MCP4XXX (2)

Comment

VDD VIH

VOH VDD

VIH

VOH

5.5

4.4

2.7

1.215 — (3)

5.0

4.0

3.0

1.35

— (3)

4.5

3.6

3.3

1.485 — (3)

3.3

2.64 2.64 4.5

2.025 — (3)

3.0

2.4

5.0

2.25

— (3)

2.7

2.16 2.16 5.5

2.475 — (3)

Note 1: VOH minimum = 0.8 * VDD;

VOL maximum = 0.6V

VIH minimum = 0.8 * VDD;

VIL maximum = 0.2 * VDD;

2: VOH minimum (SDA only) =;

VOL maximum = 0.2 * VDD

VIH minimum = 0.45 * VDD;

VIL maximum = 0.2 * VDD

3: The only MCP4XXX output pin is SDO,

which is open-drain (or open-drain with

internal pull-up) with high voltage support

Voltage

Regulator

PIC® MCU

MCP4XXX

SDI

SCK

RESET

SDI

SCK

I/O

SDO

Voltage

Regulator

PIC® MCU

MCP4XXX

SDI

SCK

RESET

SDI

SCK

I/O

SDO

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