Datasheet

MCP414X/416X/424X/426X
DS22059B-page 60 © 2008 Microchip Technology Inc.
8.2 Techniques to force the CS pin to
V
IHH
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.
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 CS
pin to go higher than the voltage such that the PIC
MCU’s IO2 pin “clamps” at approximately V
DD
.
FIGURE 8-3: Using the TC1240A to
generate the V
IHH
voltage.
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
wiper. The MCP402X Non-volatile Digital Potentiome-
ter 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 CS
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 CS
pin
(when the system voltage is approximately 5V).
FIGURE 8-4: MCP4XXX Non-volatile
Digital Potentiometer Evaluation Board
(MCP402XEV) implementation to generate the
V
IHH
voltage.
8.3 Using Shutdown Modes
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 R
BW
rheostat value to the Common B.
Disconnecting Terminal B modifies the transistor input
by the R
AW
rheostat value to the Common A. The
Common A and Common B connections could be
connected to V
DD
and V
SS
.
FIGURE 8-5: Example Application Circuit
using Terminal Disconnects.
CS
PIC MCU
MCP402X
R
1
IO1
IO2
C
2
TC1240A
V
IN
SHDN
C+
C-
V
OUT
C
1
CS
PIC10F206
MCP4XXX
R
1
GP0
GP2
C
2
C
1
Balance Bias
W
B
Input
Input
To ba se
of Transistor
(or Amplifier)
A
Common B
Common A