Datasheet

 2008-2013 Microchip Technology Inc. DS22096B-page 61
MCP453X/455X/463X/465X
8.0 APPLICATIONS EXAMPLES
Nonvolatile 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 MCP453X/455X/463X/465X
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 Techniques to force the HVC pin
to V
IHH
The circuit in Figure 8-1 shows a method using the
TC1240A doubling charge pump. When the SHDN pin
is HIGH, the TC1240A is off, and the level on the HVC
pin is controlled by the PIC
®
microcontrollers (MCUs)
IO2 pin.
When the SHDN pin is low, the TC1240A is on and the
V
OUT
voltage is 2 * V
DD
. The resistor R
1
allows the
HVC pin to go higher than the voltage such that the PIC
MCU’s IO2 pin “clamps” at approximately V
DD
.
FIGURE 8-1: Using the TC1240A to
Generate the V
IHH
Voltage.
The circuit in Figure 8-2 shows the method used on the
MCP402X nonvolatile Digital Potentiometer Evaluation
Board (Part Number: MCP402XEV). This method
requires that the system voltage be approximately 5V.
This ensures that when the PIC10F206 enters a
brown-out condition, there is an insufficient voltage
level on the HVC pin to change the stored value of the
wiper. The MCP402X nonvolatile Digital Potentiometer
Evaluation Board User’s Guide (DS51546) contains a
complete schematic.
GP0 is a general purpose I/O pin, while GP2 can either
be a general purpose I/O pin or it can output the internal
clock.
For the serial commands, configure the GP2 pin as an
input (high impedance). The output state of the GP0 pin
will determine the voltage on the HVC pin (V
IL
or V
IH
).
For high-voltage serial commands, force the GP0
output pin to output a high level (V
OH
), and configure
the GP2 pin to output the internal clock. This will form
a charge pump and increase the voltage on the HVC
pin (when the system voltage is approximately 5V).
FIGURE 8-2: MCP4XXX Nonvolatile
Digital Potentiometer Evaluation Board
(MCP402XEV) Implementation to Generate the
V
IHH
Voltage.
HVC
PIC MCU
MCP45XX
R
1
IO1
IO2
C
2
TC1240A
V
IN
SHDN
C+
C-
V
OUT
C
1
MCP46XX
HVC
PIC10F206
MCP4XXX
R
1
GP0
GP2
C
2
C
1