Microchip Technology TMPSNSRD-TCPL1 データシート
MCP9804
DS22203C-page 30
© 2009-2012 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
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 to ‘0’ to enable Continuous
Conversion mode or until power is recycled.
Conversion mode or until power is recycled.
The Shutdown bit (bit 8) cannot be set to ‘1’ while the
CONFIG<7:6> bits (Lock bits) are set to ‘1’. However, it
can be cleared to ‘0’ or returned to Continuous
Conversion mode while locked.
CONFIG<7:6> bits (Lock bits) are set to ‘1’. However, it
can be cleared to ‘0’ or returned to Continuous
Conversion mode while locked.
In Shutdown mode, all registers can be read or written.
However, the serial bus activity increases the shutdown
current. In addition, if the device is in shutdown while
the Alert pin is asserted, the device will retain the active
state during shutdown. This increases the shutdown
current due to the additional Alert output current.
However, the serial bus activity increases the shutdown
current. In addition, if the device is in shutdown while
the Alert pin is asserted, the device will retain the active
state during shutdown. This increases the shutdown
current due to the additional Alert output current.
5.2.2
TEMPERATURE HYSTERESIS
(T
(T
HYST
)
A hysteresis of 0°C, +1.5°C, +3°C or +6°C can be
selected for the T
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.
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 (CONFIG<7:6) are set to ‘1’.
Lock bits (CONFIG<7:6) are set to ‘1’.
The T
UPPER
, T
LOWER
and T
CRIT
boundary conditions
.
5.2.3
ALERT OUTPUT CONFIGURATION
The Alert output can be enabled by using bit 3 of the
CONFIG register (Alert Output Control bit) and can be
configured as either a comparator output or as an Inter-
rupt Output mode using bit 0 of CONFIG (Alert Output
Mode bit). The polarity can also be specified as active-
high or active-low using bit 1 of CONFIG (Alert Polarity
bit). This is an open-drain output and requires a pull-up
resistor.
CONFIG register (Alert Output Control bit) and can be
configured as either a comparator output or as an Inter-
rupt Output mode using bit 0 of CONFIG (Alert Output
Mode bit). The polarity can also be specified as active-
high or active-low using bit 1 of CONFIG (Alert Polarity
bit). This is an open-drain output and requires a pull-up
resistor.
When the ambient temperature increases above the
critical temperature limit, the Alert output is forced to a
comparator output (regardless of CONFIG<0>). When
the temperature drifts below the critical temperature
limit minus hysteresis, the Alert output automatically
returns to the state specified by CONFIG<0> bit.
critical temperature limit, the Alert output is forced to a
comparator output (regardless of CONFIG<0>). When
the temperature drifts below the critical temperature
limit minus hysteresis, the Alert output automatically
returns to the state specified by CONFIG<0> bit.
FIGURE 5-9:
Active-Low Alert Output
Configuration.
The status of the Alert output can be read using
CONFIG<4> (Alert Output Status bit). This bit can not
be set to ‘1’ in Shutdown mode.
CONFIG<4> (Alert Output Status bit). This bit can not
be set to ‘1’ in Shutdown mode.
Bits 7 and 6 of the CONFIG register can be used to lock
the T
the T
UPPER
, T
LOWER
and T
CRIT
registers. These bits
prevent false triggers at the Alert output due to an
accidental rewrite to these registers.
accidental rewrite to these registers.
The Alert output can also be used as a critical temper-
ature output using bit 2 of CONFIG (Alert Output Select
bit). When this feature is selected, the Alert output
becomes a comparator output. In this mode, the
interrupt output configuration (Alert Output Mode bit,
CONFIG<0>) is ignored.
ature output using bit 2 of CONFIG (Alert Output Select
bit). When this feature is selected, the Alert output
becomes a comparator output. In this mode, the
interrupt output configuration (Alert Output Mode bit,
CONFIG<0>) is ignored.
5.2.3.1
Comparator Mode
Comparator mode is selected using bit 0 of CONFIG. In
this mode, the Alert output is asserted as active-high or
active-low, using bit 1 of CONFIG.
this mode, the Alert output is asserted as active-high or
active-low, using bit 1 of CONFIG.
shows
the conditions that toggle the Alert output.
If the device enters Shutdown mode with asserted Alert
output, the output remains asserted during Shutdown
mode. The device must be operating in Continuous
Conversion mode for t
output, the output remains asserted during Shutdown
mode. The device must be operating in Continuous
Conversion mode for t
CONV
. The T
A
vs. T
UPPER
,
T
LOWER
and T
CRIT
boundary conditions need to be
satisfied in order for the Alert output to deassert.
Comparator mode is useful for thermostat type
applications, such as turning on a cooling fan or
triggering a system shutdown when the temperature
exceeds a safe operating range.
applications, such as turning on a cooling fan or
triggering a system shutdown when the temperature
exceeds a safe operating range.
MCP9804
Alert Output
R
PU
V
DD