Datasheet

© 2008 Microchip Technology Inc. DS22060B-page 59
MCP413X/415X/423X/425X
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 MCP413X/415X/423X/425X
devices can be used to replace the common mechani-
cal trim pot in applications where the operating and
terminal voltages are within CMOS process limitations
(V
DD
= 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 MCP4XXX 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 MCP4XXX device is powered by the
3.3V regulated voltage.
For SPI applications, these inputs are:
•CS
•SCK
• SDI (or SDI/SDO)
•
SHDN
Figure 8-1 through Figure 8-2 show three example split
rail systems. In this system, the MCP4XXX interface
input signals need to be able to support the PIC MCU
output high voltage (V
OH
).
In Example #1 (Figure 8-1), the MCP4XXX interface
input signals need to be able to support the PIC MCU
output high voltage (V
OH
). If the split rail voltage delta
becomes too large, then the customer may be required
to do some level shifting due to MCP4XXX V
OH
levels
related to Host Controller V
IH
levels.
In Example #2 (Figure 8-2), the MCP4XXX interface
input signals need to be able to support the lower
voltage of the PIC MCU output high voltage level (V
OH
).
Table 8-1 shows an example PIC microcontroller I/O
voltage specifications and the MCP4XXX
specifications. So this PIC MCU operating at 3.3V will
drive a V
OH
at 2.64V, and for the MCP4XXX operating
at 5.5V, the V
IH
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: V
OH
- V
IH
COMPARISONS
PIC
(1)
MCP4XXX
(2)
Comment
V
DD
V
IH
V
OH
V
DD
V
IH
V
OH
5.5 4.4 4.4 2.7 1.215 —
(3)
5.0 4.0 4.0 3.0 1.35 —
(3)
4.5 3.6 3.6 3.3 1.485 —
(3)
3.3 2.64 2.64 4.5 2.025 —
(3)
3.0 2.4 2.4 5.0 2.25 —
(3)
2.7 2.16 2.16 5.5 2.475 —
(3)
Note 1: V
OH
minimum = 0.8 * V
DD
;
V
OL
maximum = 0.6V
V
IH
minimum = 0.8 * V
DD
;
V
IL
maximum = 0.2 * V
DD
;
2: V
OH
minimum (SDA only) =;
V
OL
maximum = 0.2 * V
DD
V
IH
minimum = 0.45 * V
DD
;
V
IL
maximum = 0.2 * V
DD
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
5V
3V
PIC MCU
MCP4XXX
SDI
CS
SCK
SHDN
SDI
CS
SCK
SHDN
SDO
SDO
Voltage
Regulator
3V
5V
PIC MCU
MCP4XXX
SDI
CS
SCK
SHDN
SDI
CS
SCK
SHDN
SDO
SDO