MLX90721S 查看數據表（PDF） - Melexis Microelectronic Systems

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MLX90721S

Auto Shut Off Timer

Melexis Microelectronic Systems  

MLX90721

Auto Shut Off Timer

General Description

The chip is intended to be used for switching on and

off a mains powered device, with the added feature

of automatic switch off after a fixed amount of time.

Such device can replace conventional switches in all

appliances that might be left on inadvertently.

Besides saving energy, the main goal is to prevent

all hazards due to appliances left on unattended.

The chip is offered in a 3-pin version, where applying

the supply is switching the chip on. In its 4-pin

version, switching on and off is done with a single

push-button.

As an alternative the fourth pin can also be used as

a reset pin, where the auto-shut-off time counter is

reset when pushing this button.

The chip application version (3 or 4 pins) and auto-

shut-off time are mask programmable. The auto-

shut-off time can be almost any value between 2.5

minutes and 32 hours. The duty cycle of the relay

driver can also be adjusted by the same mask to

adapt to all types of relay construction.

Power-On-Reset.

The Power-On-Reset of the ASIC is a combination of

a digital power-on-reset with hysteresis DPOR, and

an analog APOR.

DPOR is used to initialize the logic on the chip.

The APOR is characterized by a low level – APL

signal and a high level – APH signal, which are

debounced as follows:

low level debouncing – approx. 25mS

high level debouncing – approx. 3.5mS

The digital signal APOR is a logic combination of the

debounced signals APLd and APHd. APOR is set to

High when APHd = high and APOR is reset to Low

when APLd = low.

A transition to the active state is indicated by the

digital signal APOR=1 in case of application 1 and 2,

or APOR=1 and START=1 in case of application 3.

The result is that the transistor at the pin OUT is

activated after a delay time Td , and starts switching

ON and OFF with the specified frequency F1 and

duty cycle DC1.

The digital signal APOR=0 immediately brings the

logic back to the INACTIVE state, i.e. the output is

disabled and the state of the digital output signal

from the start-stop/reset button (if present in the

particular application) is initialized to non-pressed

(released) state.

Button Input.

The Button Input can have three different functions,

which determine the three different applications:

APPL.1, APPL.2 and APPL.3. The function of the

input is defined by the options mask.

APPL.1-No Function. The BUT input is not used

and therefore not connected externally. BUT is an

internally pulled up digital input. In this case, the

transitions INACTIVE > ACTIVE state and vice

versa are defined only by the APOR signal.

LED (optional)

L

Load

N

VDD

90721

OUT

GND

Appl.1 ASO without button

APPL.2-Auto Shut-OFF Time Reset. The input

BUT can be connected to GND via an external

button. The input is an internally pulled up, active

Low, inverting digital input. In this case, the

transitions INACTIVE state > ACTIVE state and

vice versa are again defined only by the APOR

signal. Each time the button is pressed a Reset

signal is generated and the countdown for the Auto

Shut-Off Time starts from 0 again.

The state of this input ( pressed or not ) is checked

each 3.5mS. The high level (button pressed) at the

digital output is debounced for approx. 3.5mS.

LED (optional)

L

Load

VDD

90721

BUT GND OUT

N

Appl.1 ASO with time reset button

MLX90721 Auto Shut Off Timer

Page 2

Rev 1.0 22/Jun/00

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