MCP433X datasheet(79/88 Pages) MICROCHIP

79 / 88 page

 2010 Microchip Technology Inc.

DS22242A-page 79

MCP433X/435X

APPENDIX B: CHARACTERIZATION

DATA ANALYSIS

Some designers may desire to understand the device

operational characteristics outside of the specified

operating conditions of the device.

Applications where the knowledge of the resistor

network characteristics could be useful include battery

powered devices and applications that experience

brown-out conditions.

In battery applications the application voltage decays

over time until new batteries are installed. As the

voltage decays, the system will continue to operate. At

some voltage level, the application will be below its

specified operating voltage range. This is dependent

on the individual components used in the design. It is

still useful to understand the device characteristics to

expect when this low-voltage range is encountered.

Unlike a microcontroller which can use an external

supervisor device to force the controller into the Reset

state, a digital potentiometer’s resistance characteristic

is not specified. But understanding the operational

characteristics can be important in the design of the

applications circuit for this low-voltage condition.

Other application system scenarios where understand-

ing the low-voltage characteristics of the resistor net-

work could be important is for system brown out

conditions.

For the MCP433X/435X devices, the analog operation

is specified at a minimum of 2.7V. Device testing has

Terminal A connected to the device VDD (for

potentiometer configuration only) and Terminal B

connected to VSS.

B.1

Low-Voltage Operation

This

appendix

gives

overview

CMOS

semiconductor characteristics at lower voltages. This is

important

that

the

1.8V

resistor

network

characterization graphs of the MCP433X/435X devices

can be better understood.

For this discussion, we will use the 5 k

 device data.

This data was chosen since the variations of wiper

resistance has much greater implications for devices

with smaller RAB resistances.

Figure B-1 shows the worst case RBW error from the

average RBW as a percentage, while Figure B-2 shows

the RBW resistance verse wiper code graph. Nonlinear

behavior occurs at approximately wiper code 160. This

is better shown in Figure B-2, where the RBW

resistance changes from a linear slope. This change is

due to the change in the wiper resistance.

FIGURE B-1:

1.8V Worst Case RBW Error

from Average RBW (RBW0-RBW3) vs. Wiper Code

and Temperature (VDD = 1.8V, IW = 190 µA).

FIGURE B-2:

RBW vs. Wiper Code And

Temperature (VDD = 1.8V, IW = 190 µA).

-7.00%

-6.00%

-5.00%

-4.00%

-3.00%

-2.00%

-1.00%

0.00%

1.00%

2.00%

128

160

192

224

256

Wiper Code

-40C

+25C

+85C

+125C

1000

2000

3000

4000

5000

6000

7000

128

160

192

224

256

Wiper Code

-40C

+25C

+85C

+125C

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