MCP9808 MICROCHIP [Microchip Technology], MCP9808 Datasheet - Page 30

• Manufacturer Part Number: MCP9808
• Manufacturer: MICROCHIP [Microchip Technology]

MCP9808
5.2
5.2.1
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
until bit 8 is cleared to ‘0’ to enable Continuous
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.
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.
5.2.2
A hysteresis of 0°C, +1.5°C, +3°C or +6°C can be
selected for the T
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 (CONFIG<7:6) are set to ‘1’.
The T
are described graphically in
5.2.3
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
Interrupt 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.
DS25095A-page 30
UPPER
SENSOR FEATURE DESCRIPTION
SHUTDOWN MODE
TEMPERATURE HYSTERESIS
(T
ALERT OUTPUT CONFIGURATION
, T
HYST
LOWER
UPPER
)
and T
SHDN
, T
LOWER
Figure
. It remains in this mode
CRIT
and T
boundary conditions
5-10.
CRIT
temperate
FIGURE 5-9:
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.
Bits 7 and 6 of the CONFIG register can be used to lock
the T
prevent false triggers at the Alert output due to an
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.
5.2.3.1
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.
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
T
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.
LOWER
UPPER
Alert Output
and T
, T
Comparator Mode
LOWER
CRIT
V
DD
boundary conditions need to be
R
and T
Active-Low Alert Output
PU
© 2011 Microchip Technology Inc.
CONV
CRIT
. The T
registers. These bits
MCP9808
Figure 5-10
A
vs. T
UPPER
shows
,