LM77

SNIS103F – JUNE 1999 – REVISED MARCH 2013

www.ti.com

Avoid programming setpoints so close that their hysteresis values overlap. An example would be that with a

THYST value of 2°C then setting THIGH and TLOW to within 4°C of each other will violate this restriction. To be more

specific, with THYST set to 2°C assume THIGH set to 64°C. If TLOW is set equal to, or higher than 60°C this

restriction is violated.

DEFAULT SETTINGS

The LM77 always powers up in a known state. LM77 power up default conditions are:

1. Comparator Interrupt Mode

2. TLOW set to 10°C

3. THIGH set to 64°C

4. T_CRIT set to 80°C

5. THYST set to 2°C

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 following curve. The LM77 registers will reset

again when the power supply drops below the voltage plotted in this curve.

Average Power on Reset Voltage vs Temperature

Figure 6.

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 address. 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 +VS for a high, (1).

Therefore, the complete slave address is:

1

0

0

1

0

A1

A0

MSB

LSB

8

Submit Documentation Feedback

Copyright © 1999–2013, Texas Instruments Incorporated

Product Folder Links: LM77