MCP9800A1 View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

MCP9800A1

2-Wire High-Accuracy Temperature Sensor

Microchip Technology 

MCP9800/1/2/3

5.3.4.1 Shutdown Mode

The Shutdown mode disables all power-consuming

activities (including temperature sampling operations)

while leaving the serial interface active. The device

consumes 2 µA (maximum) 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 to; however, the serial

bus activity will increase the shutdown current.

5.3.4.2 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

register. The One-shot mode performs a single

temperature measurement and returns to Shutdown

mode. This mode is especially useful for low-power

applications where temperature is measured upon

command from a controller. For example, a 9-bit TA in

One-shot mode consumes 200 µA (typical) for 30 ms

and 0.1 µA (typical) 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, the

CONFIG register needs to be written to again, with bit

0 and bit 7 set <1>. This begins the single conversion

cycle of tCONV, 30ms 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 5-2: SHUTDOWN AND ONE-SHOT

MODE DESCRIPTION

Operational Mode

One-Shot Shutdown

(Bit 7)

(Bit 0)

Continuous Conversion

0

0

Shutdown

0

1

Continuous Conversion

1

0

(One-shot is ignored)

One-shot (Note 1)

1

1

Note 1: The shutdown command <01> needs to

be programmed before sending a

one-shot command <11>.

5.3.4.3 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, while

Figure 5-7 gives a graphical description.

5.3.4.4 Comparator Mode

In 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 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.

5.3.4.5 Interrupt Mode

In 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

register. This mode is designed for interrupt-driven,

microcontroller-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.

TSET

TA

THYST

ALERT

Comparator mode

Active-low

ALERT

Interrupt mode

Active-low

Register

*

Read

* See Section 5.3.4.5 “Interrupt Mode”

FIGURE 5-7:

Alert Output.

DS21909D-page 24

 2010 Microchip Technology Inc.

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