MCP9803 datasheet(14/30 Pages) MICROCHIP

14 / 30 page

MCP9800/1/2/3

DS21909B-page 14

 2004 Microchip Technology Inc.

4.3.4.1

Shutdown Mode

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, TA, TSET and THYST

registers can be read or written. However, the serial

bus activity will increase the shutdown current.

4.3.4.2

One-Shot Mode

The MCP9800/1/2/3 can also be used in a One-shot

mode that can be selected using bit 7 of the CONFIG

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 TA in One-shot

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, TA is updated and bit 7 of CONFIG

becomes cleared <0> by the MCP9800/1/2/3.

TABLE 4-6:

SHUTDOWN AND ONE-SHOT

MODE DESCRIPTION

4.3.4.3

ALERT Output Configuration

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

Comparator Mode

In the Comparator mode, the ALERT output is asserted

when TA is greater than TSET. The pin remains active

until TA is lower than THYST. The 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.

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 TA

below THYST, for the ALERT output to be deasserted.

4.3.4.5

Interrupt Mode

In the Interrupt mode, the ALERT output is asserted

when TA is greater than TSET. However, the output is

deasserted when the user performs a read from any

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 TA drifts below THYST, the MCP9800/

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:

Alert Output.

Operational Mode

One-Shot

(Bit 7)

Shutdown

(Bit 0)

Continuous Conversion

Shutdown

Continuous Conversion

(One-shot is ignored)

One-Shot

Note:

The shutdown command <01> needs to

be programmed before sending a one-

shot command <11>.

TSET

THYST

ALERT

Comparator Mode

Interrupt Mode

Active-Low

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