MCP45HVX1 Datasheet, PDF (66/100 Pages) Microchip Technology – Single-Resistor Network

MCP45HVX1
8.0 APPLICATIONS EXAMPLES
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.
8.1 Using Shutdown Modes
Figure 8-1 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+ and V-.
Input
Common A
A
To base
W
of Transistor
(or Amplifier)
B
Input
Common B
Balance
Bias
FIGURE 8-1:
Example Application Circuit
using Terminal Disconnects.
DS20005304A-page 66
8.2 Software Reset Sequence
Note: This technique is documented in AN1028.
At times, it may become necessary to perform a
Software Reset Sequence to ensure the MCP45HVX1
device is in a correct and known I²C Interface state.
This technique only resets the I²C state machine.
This is useful if the MCP45HVX1 device powers-up in
an incorrect state (due to excessive bus noise, etc), or
if the master device is reset during communication.
Figure 8-2 shows the communication sequence to
software reset the device.
S ‘1’ ‘1’ ‘1’ ‘1’ ‘1’ ‘1’ ‘1’ ‘1’ S P
Start
bit
Nine bits of ‘1’
Start bit
Stop bit
FIGURE 8-2:
Software Reset Sequence
Format.
The first Start bit will cause the device to reset from a
state in which it is expecting to receive data from the
master device. In this mode, the device is monitoring
the data bus in Receive mode and can detect the Start
bit forces an internal Reset.
The nine bits of ‘1’ are used to force a Reset of those
devices that could not be reset by the previous Start bit.
This occurs only if the MCP45HVX1 is driving an A bit
on the I²C bus, or is in Output mode (from a Read
command) and is driving a data bit of ‘0’ onto the I²C
bus. In both of these cases, the previous Start bit could
not be generated due to the MCP45HVX1 holding the
bus Low. By sending out nine ‘1’ bits, it is ensured that
the device will see an A bit (the master device does not
drive the I²C bus Low to acknowledge the data sent by
the MCP45HVX1), which also forces the MCP45HVX1
to reset.
The second Start bit is sent to address the rare possi-
bility of an erroneous write. This could occur if the mas-
ter device was reset while sending a Write command to
the MCP45HVX1, and then as the master device
returns to normal operation and issues a Start condition
while the MCP45HVX1 is issuing an Acknowledge. In
this case, if the 2nd Start bit is not sent (and the Stop bit
was sent) the MCP45HVX1 could initiate a write cycle.
M
Note:
The potential for this erroneous write only
occurs if the master device is reset while
sending a Write command to the
MCP45HVX1.
The Stop bit terminates the current I²C bus activity. The
MCP45HVX1 waits to detect the next Start condition.
This sequence does not effect any other I²C devices
which may be on the bus, as they should disregard this
as an invalid command.
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