TCN75AVOA datasheet(21/32 Pages) MICROCHIP

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DS21935C-page 21

TCN75A

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 (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 to; however, the serial

bus activity will increase the shutdown current.

5.3.4.2

One-Shot Mode

The TCN75A 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 (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, 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 TCN75A.

TABLE 5-6:

SHUTDOWN AND ONE-SHOT

MODE DESCRIPTION

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 5-6 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 inter-

rupt will have to acknowledge the interrupt by reading

any register from the TCN75A. This will clear the interrupt

and the ALERT pin will become deasserted. When TA

drifts below THYST, the TCN75A 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 5-6:

Alert Output.

Operational Mode

One-Shot

(Bit 7)

Shutdown

(Bit 0)

Continuous Conversion

Shutdown

Continuous Conversion

(One-shot is ignored)

One-shot (Note 1)

Note 1: The shutdown command <01> needs to

be programmed before sending a one-

shot command <11>.

TSET

THYST

ALERT

Comparator mode

Interrupt mode

Active-low

Read

* See Section 5.3.4.5 “Interrupt Mode”

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