HCS361_11 datasheet(15/42 Pages) MICROCHIP

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DS40146F-page 15

HCS361

5.4

Auto-shutoff

The Auto-shutoff function automatically stops the

device from transmitting if a button inadvertently gets

pressed for a long period of time. This will prevent the

device from draining the battery if a button gets

pressed while the transmitter is in a pocket or purse.

This function can be enabled or disabled and is

selected by setting or clearing the time-out bit

(Section 3.5.13). Setting this bit will enable the function

(turn Auto-shutoff function on) and clearing the bit will

disable the function. Time-out period is approximately

25 seconds.

5.5

VLOW: Voltage LOW Indicator

The VLOW bit is transmitted with every transmission

(Figure 3-2) and will be transmitted as a one if the

operating voltage has dropped below the low voltage

trip point, typically 3.8V at 25°C. This VLOW signal is

transmitted so the receiver can give an indication to the

user that the transmitter battery is low.

5.6

LED Output Operation

During normal transmission the LED output is LOW

while the data is being transmitted and high during the

guard time. Two voltage indications are combined into

one bit: VLOW. Table 5-1 indicates the operation value

of VLOW while data is being transmitted.

FIGURE 5-2:

VLOW Trip Point VS.

Temperature

If the supply voltage drops below the low voltage trip

point, the LED output will be toggled at approximately

1Hz during the transmission.

TABLE 5-1:

VLOW AND LED VS. VDD

*See also FLASH operating modes.

Approximate

Supply Voltage

Vlow Bit

LED Operation*

Max

→3.8V

Normal

3.8V

→2.2V

Flashing

2.2V

→Min

Normal

3.5

-40

VLOW=0

Nominal Trip Point

3.8V

VLOW=1

VLOW=0

Nominal Trip

Point

4.5

3.5

2.5

1.5

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