Datasheet

© 2009 Microchip Technology Inc. DS22152B-page 31
MCP40D17/18/19
4.0 GENERAL OVERVIEW
The MCP40D17/18/19 devices are general purpose
digital potentiometers intended to be used in
applications where a programmable resistance with
moderate bandwidth is desired.
This Data Sheet covers a family of three Digital
Potentiometer and Rheostat devices. The MCP40D18
device is the Potentiometer configuration, while the
MCP40D17 and MCP40D19 devices are the Rheostat
configuration.
Applications generally suited for the MCP40D17/18/19
devices include:
• Computer Servers
• Set point or offset trimming
• Sensor calibration
• Selectable gain and offset amplifier designs
• Cost-sensitive mechanical trim pot replacement
As the Device Block Diagram shows, there are four
main functional blocks. These are:
• POR/BOR Operation
• Serial Interface - I
2
C Module
• Resistor Network
The POR/BOR operation and the Memory Map are
discussed in this section and the I
2
C and Resistor
Network operation are described in their own sections.
The Serial Commands commands are discussed in
Section 5.4.
4.1 POR/BOR Operation
The Power-on Reset is the case where the device is
having power applied to it from V
SS
. The Brown-out
Reset occurs when a device had power applied to it,
and that power (voltage) drops below the specified
range.
The devices RAM retention voltage (V
RAM
) is lower
than the POR/BOR voltage trip point (V
POR
/V
BOR
). The
maximum V
POR
/V
BOR
voltage is less than 1.8V.
When V
POR
/V
BOR
< V
DD
< 2.7V, the Resistor Network’s
electrical performance may not meet the data sheet
specifications. In this region, the device is capable of
reading and writing to its volatile memory if the proper
serial command is executed.
Table 4-1 shows the digital pot’s level of functionality
across the entire V
DD
range, while Figure 4-1 illustrates
the Power-up and Brown-out functionality.
4.1.1 POWER-ON RESET
When the device powers up, the device V
DD
will cross
the V
POR
/V
BOR
voltage. Once the V
DD
voltage crosses
the V
POR
/V
BOR
voltage, the following happens:
• Volatile wiper register is loaded with the default
wiper value (3Fh)
• The device is capable of digital operation
4.1.2 BROWN-OUT RESET
When the device powers down, the device V
DD
will
cross the V
POR
/V
BOR
voltage. Once the V
DD
voltage
decreases below the V
POR
/V
BOR
voltage the following
happens:
• Serial Interface is disabled
If the V
DD
voltage decreases below the V
RAM
voltage
the following happens:
• Volatile wiper registers may become corrupted
As the voltage recovers above the V
POR
/V
BOR
voltage
see Section 4.1.1 “Power-on Reset”.
Serial commands not completed due to a Brown-out
condition may cause the memory location to become
corrupted.
4.1.3 WIPER REGISTER (RAM)
The Wiper Register is volatile memory that starts
functioning at the RAM retention voltage (V
RAM
). The
Wiper Register will be loaded with the default wiper
value when V
DD
will rise above the V
POR
/V
BOR
voltage.
4.1.4 DEVICE CURRENTS
The current of the device can be classified into two
modes of the device operation. These are:
• Serial Interface Inactive (Static Operation)
• Serial Interface Active
Static Operation occurs when a Stop condition is
received. Static Operation is exited when a Start
condition is received.