MCP413X/415X/423X/425X
8.2
Techniques to force the CS pin to
VIHH
PIC10F206
R1
GP0
The circuit in Figure 8-3 shows a method using the
TC1240A doubling charge pump. When the SHDN pin
is high, the TC1240A is off, and the level on the CS pin
is controlled by the PIC® microcontrollers (MCUs) IO2
pin.
MCP4XXX
GP2
CS
C1
When the SHDN pin is low, the TC1240A is on and the
VOUT voltage is 2 * VDD. The resistor R1 allows the CS
pin to go higher than the voltage such that the PIC
MCU’s IO2 pin “clamps” at approximately VDD.
C2
FIGURE 8-4:
MCP4XXX Non-Volatile
Digital Potentiometer Evaluation Board
(MCP402XEV) implementation to generate the
TC1240A
VIN
V
voltage.
IHH
C+
PIC MCU
C1
C-
SHDN
8.3
Using Shutdown Modes
VOUT
IO1
Figure 8-5 shows a possible application circuit where
the independent terminals could be used.
Disconnecting the wiper allows the transistor input to
be taken to the Bias voltage level (disconnecting A and
or B may be desired to reduce system current).
Disconnecting Terminal A modifies the transistor input
by the RBW rheostat value to the Common B.
Disconnecting Terminal B modifies the transistor input
by the RAW rheostat value to the Common A. The
Common A and Common B connections could be
MCP402X
R1
CS
IO2
C2
FIGURE 8-3:
generate the V
Using the TC1240A to
voltage.
IHH
connected to VDD and VSS
.
The circuit in Figure 8-4 shows the method used on the
MCP402X Non-volatile Digital Potentiometer Evalua-
tion 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 CS pin to change the stored value of the
Common A
Input
wiper.
The
MCP402X
Non-volatile
Digital
A
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.
To base
of Transistor
(or Amplifier)
W
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 CS pin (VIL or VIH).
For high-voltage serial commands, force the GP0
output pin to output a high level (VOH) and configure the
GP2 pin to output the internal clock. This will form a
charge pump and increase the voltage on the CS pin
(when the system voltage is approximately 5V).
B
Input
Common B
Balance
Bias
Example Application Circuit
FIGURE 8-5:
using Terminal Disconnects.
DS22060B-page 60
© 2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
