MCP9802 Microchip Technology Inc., MCP9802 Datasheet - Page 14

• Manufacturer Part Number: MCP9802
• Description: 2-wire High-accuracy Temperature Sensor
• Manufacturer: Microchip Technology Inc.

MCP9800/1/2/3
4.3.4.1
The Shutdown mode disables all power-consuming
activities (including temperature sampling operations)
while leaving the serial interface active. The device
consumes 1 µA (max.) in this mode. It remains in this
mode until the configuration register is updated to
enable continuous conversion or until power is
recycled.
In Shutdown mode, the CONFIG, T
registers can be read or written. However, the serial
bus activity will increase the shutdown current.
4.3.4.2
The MCP9800/1/2/3 can also be used in a One-shot
mode that can be selected using bit 7 of the CONFIG
register. The One-shot mode performs a single temper-
ature measurement and returns to Shutdown mode.
This mode is especially useful for low-power applica-
tions where temperature is measured upon command
from a controller. For example, a 9-bit T
mode consumes 200 µA (typ.) for 30 ms and 0.1 µA
(typ.) during shutdown.
To access this feature, the device needs to initially be
in Shutdown mode. This is done by sending a byte to
the CONFIG register with bit 0 set <1> and bit 7
cleared <0>. Once the device is in Shutdown mode,
CONFIG needs to be written again with bit 0 and bit 7
set <1>. This begins the single conversion cycle of
30 ms for 9-bit data. Once the conversion is
completed, T
becomes cleared <0> by the MCP9800/1/2/3.
TABLE 4-6:
DS21909B-page 14
Continuous Conversion
Shutdown
Continuous Conversion
(One-shot is ignored)
One-Shot
Note:
Operational Mode
The shutdown command <01> needs to
be programmed before sending a one-
shot command <11>.
Shutdown Mode
One-Shot Mode
A
is updated and bit 7 of CONFIG
SHUTDOWN AND ONE-SHOT
MODE DESCRIPTION
One-Shot
(Bit 7)
0
0
1
1
A
, T
SET
A
in One-shot
Shutdown
and T
(Bit 0)
0
1
0
1
HYST
4.3.4.3
The ALERT output can be configured as either a
comparator output or as Interrupt Output mode using
bit 1 of CONFIG. The polarity can also be specified as
an active-high or active-low, using bit 2 of CONFIG.
The following sections describe each Output mode
and Figure 4-2 shows graphical description.
4.3.4.4
In the Comparator mode, the ALERT output is asserted
when T
until T
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.
In the Comparator mode, if the device enters the
Shutdown mode with asserted ALERT output, the
output remains active during shutdown. The device
must be operating in continuous conversion, with T
below T
4.3.4.5
In the Interrupt mode, the ALERT output is asserted
when T
deasserted when the user performs a read from any
register. This mode is designed for interrupt driven micro-
controller based systems. The microcontroller receiving
the interrupt will have to acknowledge the interrupt by
reading any register from the MCP9800/1/2/3. This will
clear the interrupt and the ALERT pin will become
deasserted. When T
1/2/3 outputs another interrupt and the controller needs
to read a register to deassert the ALERT output. Shutting
down the device will also reset or deassert the ALERT
output.
FIGURE 4-2:
Interrupt Mode
T
ALERT
T
T
ALERT
Comparator Mode
SET
A
HYST
Active-Low
Active-Low
A
A
A
HYST
is lower than T
is greater than T
is greater than T
, for the ALERT output to be deasserted.
ALERT Output Configuration
Comparator Mode
Interrupt Mode
A
drifts below T
Alert Output.
HYST
 2004 Microchip Technology Inc.
SET
SET
. The Comparator mode is
. The pin remains active
. However, the output is
HYST
, the MCP9800/
A