terrupts just after reprogramming setpoints. Typically, sys-

tem Interrupt inputs are masked prior to reprogramming trip

points. By doing a read just after resetting trip points, but

prior to unmasking, unexpected Interrupts are prevented.

Avoid programming setpoints so close that their hysteresis

values overlap. An example would be that with a T

of 2˚C then setting T

other will violate this restriction. To be more specific, with

T

HYST

set to 2˚C assume T

equal to, or higher than 60˚C this restriction is violated.

1.2 DEFAULT SETTINGS

The LM77 always powers up in a known state. LM77 power

up default conditions are:

1.

Comparator Interrupt Mode

2.

T

3.

T

4.

T_CRIT set to 80˚C

5.

T

6.

INT and T_CRIT_A active low

7.

Pointer set to “00”; Temperature Register

The LM77 registers will always reset to these default values

when the power supply voltage is brought up from zero volts

as the supply crosses the voltage level plotted in the follow-

ing curve. The LM77 registers will reset again when the

power supply drops below the voltage plotted in this curve.

1.3 SERIAL BUS INTERFACE

The LM77 operates as a slave on the Serial Bus, so the SCL

line is an input (no clock is generated by the LM77) and the

SDA line is a bi-directional serial data line. According to

Serial Bus specifications, the LM77 has a 7-bit slave ad-

dress. The five most significant bits of the slave address are

hard wired inside the LM77 and are “10010”. The two least

significant bits of the address are assigned to pins A1–A0,

and are set by connecting these pins to ground for a low, (0);

or to +V

Therefore, the complete slave address is:

10010

A1

A0

MSB

LSB

Average Power on Reset Voltage

vs Temperature

DS100136-18

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