Datasheet

MCP4021/2/3/4
DS21945E-page 28 © 2006 Microchip Technology Inc.
4.2 The WiperLock™ Technology
The MCP4021/2/3/4 device’s WiperLock technology
allows application-specific calibration settings to be
secured in the EEPROM without requiring the use of an
additional write-protect pin.
The WiperLock technology prevents the serial
commands from doing the following:
• Incrementing or decrementing the wiper setting
• Writing the wiper setting to the non-volatile
memory
Enabling and disabling the WiperLock technology
feature requires high-voltage serial commands
(CS
=V
IHH
). Incrementing and decrementing the wiper
requires high-voltage commands when the feature is
enabled. The high-voltage threshold (V
IHH
) is intended
to prevent the wiper setting from being altered by noise
or intentional transitions on the U/D
and CS pins, while
still providing flexibility for production or calibration
environments.
Both the CS
and U/D input pins are tolerant of signals
up to 12V. This allows the flexibility to multiplex the
digital pot’s control signals onto application signals for
manufacturing/calibration.
4.3 Power-up
When the device powers up, the last saved wiper
setting is restored.
While V
DD
< V
min
(2.7V), the electrical performance
may not meet the data sheet specifications (see
Figure 4-2). The wiper may be unknown or initialized to
the value stored in the EEPROM. Also the device may
be capable of incrementing, decrementing and writing
to its EEPROM, if a valid command is detected on the
CS
and U/D pins.
The default settings of the MCP4021/2/3/4 device’s
from the factory are shown in Ta b le 4- 1.
TABLE 4-1: DEFAULT FACTORY
SETTINGS SELECTION
It is good practice in your manufacturing flow to
configure the device to your desired settings.
4.4 Brown Out
If the device V
DD
is below the specified minimum
voltage, care must be taken to ensure that the CS and
U/D pins do not “create” any of the serial commands.
When the device V
DD
drops below V
min
(2.7V), the
electrical performance may not meet the data sheet
specifications (see Figure 4-2). The wiper may be
unknown or initialized to the value stored in the
EEPROM. Also the device may be capable of
incrementing, decrementing and writing to its EEPROM
if a valid command is detected on the CS
and U/D pins.
4.5 Serial Interface Inactive
The serial interface is inactive any time the CS pin is at
V
IH
and all write cycles are completed.
FIGURE 4-2: Power-up and Brown-out.
Package
Code
Default
POR
Wiper
Setting
Wiper
Code
WiperLock™
Technology
Setting
Typical
R
AB
Value
-202 Mid-scale 1Fh Disabled 2.1 kΩ
-502 Mid-scale 1Fh Disabled 5.0 kΩ
-103 Mid-scale 1Fh Disabled 10.0 kΩ
-503 Mid-scale 1Fh Disabled 50.0 kΩ
V
WP
V
SS
V
DD
2.7V
EEPROM
Write
Protect
Outside
Specified AC/DC
Range