Datasheet

MCP9843/98243
DS22153C-page 32 © 2009 Microchip Technology Inc.
5.2 SENSOR FEATURE DESCRIPTION
5.2.1 SHUTDOWN MODE
Shutdown mode disables all power-consuming
activities (including temperature sampling operations)
while leaving the serial interface active. This mode is
selected by setting bit 8 of CONFIG to ‘1’. In this mode,
the device consumes I
SHDN
. It remains in this mode
until bit 8 is cleared ‘0’ to enable Continuous
Conversion mode, or until power is recycled.
The Shutdown bit (bit 8) cannot be set to ‘1’ while bits
6 and 7 of CONFIG (Lock bits) are set to ‘1’. However,
it can be cleared ‘0’ or returned to Continuous
Conversion while locked.
In Shutdown mode, all registers can be read or written.
However, the serial bus activity increases the shutdown
current.
If the device is shutdown while the Event pin is
asserted, then the Event output will be de-asserted
during shutdown. It will remain de-asserted until the
device is enabled for normal operation. Once the
device is enabled it takes tCONV before the device
re-asserts the Event output.
5.2.2 TEMPERATURE HYSTERESIS
(T
HYST
)
A hysteresis of 0°C, 1.5°C, 3°C or 6°C can be selected
for the T
UPPER
, T
LOWER
and T
CRIT
temperate
boundaries using bits 10 and 9 of CONFIG. The
hysteresis applies for decreasing temperature only (hot
to cold), or as temperature drifts below the specified
limit.
The hysteresis bits can not be changed if either of the
lock bits, bits 6 and 7 of CONFIG, are set to ‘1’.
The T
UPPER
, T
LOWER
and T
CRIT
boundary conditions
are described graphically in Figure 5-2.
5.2.3 EVENT OUTPUT CONFIGURATION
The Event output can be enabled using bit 3 of
CONFIG (Event output control bit) and can be
configured as either a comparator output or as Interrupt
Output mode using bit 0 of CONFIG (Event mode). The
polarity can also be specified as an active-high or
active-low using bit 1 of CONFIG (Event polarity).
When active-high output is selected, a pull-down
resistor is requried on the Event pin. When active-low
output is selected, a pull-up resistor is required on the
Event pin, see Figure 5-10 and Figure 5-11 for
graphical circuit description. These configurations are
designed to serve processors with Low-to-High or
High-to-Low edge triggered inputs. With these
configurations, when the Event output De-asserts,
power will not be dissipated across the pull-up or
pull-down resistors.
When the ambient temperature increases above the
critical temperature limit, the Event output is forced to a
comparator output (regardless of bit 0 of CONFIG).
When the temperature drifts below the critical
temperature limit minus hysteresis, the Event output
automatically returns to the state specified by bit 0 of
CONFIG.
FIGURE 5-10: Active-High Event Output
Configuration.
FIGURE 5-11: Active-Low Event Output
Configuration.
The status of the Event output can be read using bit 4
of CONFIG (Event status). This bit can not be set to ‘1’
in shutdown mode.
Bit 7 and 6 of the CONFIG register can be used to lock
the T
UPPER
, T
LOWER
and T
CRIT
registers. The bits
prevent false triggers at the Event output due to an
accidental rewrite to these registers.
The Event output can also be used as a critical
temperature output using bit 2 of CONFIG (critical
output only). When this feature is selected, the Event
output becomes a comparator output. In this mode, the
interrupt output configuration (bit 0 of CONFIG) is
ignored.
MCP9843/98243
Event Output
R
PD
V
DD
MCP9843/98243
Event Output
R
PU
V
DD