Datasheet

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
T
HYST
value of 2°C then setting T
HIGH
and T
LOW
to within 4°C of each other will violate this restriction. To be more
specific, with T
HYST
set to 2°C assume T
HIGH
set to 64°C. If T
LOW
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. T
LOW
set to 10°C
3. T
HIGH
set to 64°C
4. T_CRIT set to 80°C
5. T
HYST
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 +V
S
for a high, (1).
Therefore, the complete slave address is:
1 0 0 1 0 A1 A0
MSB LSB
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