Datasheet

© 2006 Microchip Technology Inc. DS21945E-page 41
MCP4021/2/3/4
5.3 CS High Voltage
Depending on the requirements of the system, the use
of high voltage (V
IHH
) on the CS pin, may or may not be
required during system operation. Table 5-2 shows
possible system applications, and whether a high
voltage (V
IHH
) is required on the system.
The MCP402X supports six high-voltage commands
(the CS
input voltage must meet the VIHH
specification).
TABLE 5-2: HIGH-VOLTAGE
APPLICATIONS
5.3.1 TECHNIQUES TO FORCE THE CS
PIN TO V
IHH
The circuit in Figure 5-12 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 5-12: Using the TC1240A to
generate the V
IHH
voltage.
The circuit in Figure 5-13 shows the method used on
the MCP402X Non-volatile Digital Potentiometer
Evaluation Board. This method requires that the
system voltage be approximately 5V. This ensures that
when the PIC10F206 enters a brown-out condition,
there is an insufficent voltage level on the CS
pin to
change the stored value of the wiper. The MCP402X
Non-volatile 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 impedence). 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 5-13: MCP402X Non-volatile
Digital Potentiometer Evaluation Board
(MCP402XEV) implementation to generate the
V
IHH
voltage.
System Operation
High
Voltage
Production calibration only - system
should not update wiper setting
From
Calibration
Unit
WiperLock™ Technogy disabled during
system operation
Not
Required
Wiper setting can be updated and
“locked” during system operation
Required
CS
PIC
®
MCU
MCP402X
R
1
IO1
IO2
C
2
TC1240A
V
IN
SHDN
C+
C-
V
OUT
C
1
CS
PIC10F206
MCP402X
R
1
GP0
GP2
C
2
C
1