MCP413X/415X/423X/425X
8.0
APPLICATIONS EXAMPLES
5V
3V
Voltage
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
(VDD = 2.7V to 5.5V).
Regulator
MCP4XXX
PIC MCU
SDI
CS
SCK
SDI
CS
SCK
SHDN
SDO
SHDN
SDO
FIGURE 8-1:
System 1.
Example Split Rail
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.
5V
Voltage
Regulator
3V
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.
MCP4XXX
PIC MCU
SDI
CS
SCK
SDI
CS
SCK
For SPI applications, these inputs are:
• CS
SHDN
SDO
SHDN
SDO
• SCK
• SDI (or SDI/SDO)
• SHDN
FIGURE 8-2:
Example Split Rail
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 (VOH).
System 2.
TABLE 8-1:
PIC (1)
V
- V COMPARISONS
OH
IH
MCP4XXX (2)
In Example #1 (Figure 8-1), the MCP4XXX interface
input signals need to be able to support the PIC MCU
output high voltage (VOH). If the split rail voltage delta
becomes too large, then the customer may be required
to do some level shifting due to MCP4XXX VOH levels
related to Host Controller VIH levels.
Comment
VDD VIH VOH VDD VIH
VOH
5.5
5.0
4.5
3.3
3.0
2.7
4.4
4.0
3.6
4.4
4.0
3.6
2.7 1.215 — (3)
(3)
3.0 1.35
—
3.3 1.485 — (3)
2.64 2.64 4.5 2.025 — (3)
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 (VOH).
(3)
2.4
2.4
5.0 2.25
—
2.16 2.16 5.5 2.475 — (3)
Note 1: VOH minimum = 0.8 * VDD
;
Table 8-1 shows an example PIC microcontroller I/O
VOL maximum = 0.6V
voltage
specifications
and
the
MCP4XXX
VIH minimum = 0.8 * VDD
VIL maximum = 0.2 * VDD
;
;
specifications. So this PIC MCU operating at 3.3V will
drive a VOH at 2.64V, and for the MCP4XXX operating
at 5.5V, the VIH is 2.47V. Therefore, the interface
signals meet specifications.
2: VOH minimum (SDA only) =;
VOL maximum = 0.2 * VDD
VIH minimum = 0.45 * VDD
VIL maximum = 0.2 * VDD
;
3: The only MCP4XXX output pin is SDO,
which is Open-Drain (or Open-Drain with
Internal Pull-up) with High Voltage Support
© 2008 Microchip Technology Inc.
DS22060B-page 59
MICROCHIP [ MICROCHIP ]
