Datasheet

© 2009 Microchip Technology Inc. DS22233A-page 61
MCP434X/436X
8.0 APPLICATIONS EXAMPLES
Non-volatile digital potentiometers have a multitude of
practical uses in modern electronic circuits. The most
popular uses include precision calibration of set point
thresholds, sensor trimming, LCD bias trimming, audio
attenuation, adjustable power supplies, motor control
overcurrent trip setting, adjustable gain amplifiers and
offset trimming. The MCP434X/436X devices can be
used to replace the common mechanical 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 MCP43XX 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 MCP43XX device is powered by the
3.3V regulated voltage.
For SPI applications, these inputs are:
•CS
•SCK
• SDI (or SDI/SDO)
•WP
• RESET
Figure 8-1 through Figure 8-2 show three example split
rail systems. In this system, the MCP43XX interface
input signals need to be able to support the PIC MCU
output high voltage (V
OH
).
In Example #1 (Figure 8-1), the MCP43XX 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 MCP43XX V
OH
levels
related to Host Controller V
IH
levels.
In Example #2 (Figure 8-2), the MCP43XX 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 MCP43XX
specifications. So this PIC MCU operating at 3.3V will
drive a V
OH
at 2.64V, and for the MCP43XX 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
WP
RESET
SDI
CS
SCK
WP
I/O
SDO
SDO
Voltage
Regulator
3V
5V
PIC MCU
MCP4XXX
SDI
CS
SCK
WP
RESET
SDI
CS
SCK
WP
I/O
SDO
SDO