Datasheet

© 2009 Microchip Technology Inc. DS22152B-page 45
MCP40D17/18/19
6.4 Operational Characteristics
Understanding the operational characteristics of the
device’s resistor components is important to the system
design.
6.4.1 ACCURACY
6.4.1.1 Integral Non-linearity (INL)
INL error for these devices is the maximum deviation
between an actual code transition point and its
corresponding ideal transition point after offset and
gain errors have been removed. These endpoints are
from 0x00 to 0x7F. Refer to Figure 6-5.
Positive INL means higher resistance than ideal.
Negative INL means lower resistance than ideal.
FIGURE 6-5: INL Accuracy.
6.4.1.2 Differential Non-linearity (DNL)
DNL error is the measure of variations in code widths
from the ideal code width. A DNL error of zero would
imply that every code is exactly 1 LSb wide.
FIGURE 6-6: DNL Accuracy.
6.4.1.3 Ratiometric temperature coefficient
The ratiometric temperature coefficient quantifies the
error in the ratio R
AW
/R
WB
due to temperature drift.
This is typically the critical error when using a
potentiometer device (MCP40D18) in a voltage divider
configuration.
6.4.1.4 Absolute temperature coefficient
The absolute temperature coefficient quantifies the
error in the end-to-end resistance (Nominal resistance
R
AB
) due to temperature drift. This is typically the
critical error when using a rheostat device (MCP40D17
and MCP40D19) in an adjustable resistor
configuration.
111
110
101
100
011
010
001
000
Digital
Input
Code
Actual
transfer
function
INL < 0
Ideal transfer
function
INL < 0
Digital Pot Output
111
110
101
100
011
010
001
000
Digital
Input
Code
Actual
transfer
function
Ideal transfer
function
Narrow code < 1 LSb
Wide code, > 1 LSb
Digital Pot Output