LM77-3EVAL National Semiconductor, LM77-3EVAL Datasheet - Page 7

• Manufacturer Part Number: LM77-3EVAL
• Description: EVALUATION BOARD FOR LM77-3
• Manufacturer: National Semiconductor

Specifications of LM77-3EVAL

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM77-3EVAL

For example, if a user never read the part, and temperature
went below T
that way forever if a user never read the part.
However if the user read the part, the output would be reset.
Even if the condition is true, it will remain reset. The temper-
ature must cross above T
In either mode, reading any register in the LM77 restarts the
conversion. This allows a designer to know exactly when the
LM77 begins a comparison. This prevents unnecessary In-
terrupts just after reprogramming setpoints. Typically, system
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
will violate this restriction. To be more specific, with T
to 2°C assume T
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.
2.
3.
4.
5.
6.
7.
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.
Comparator Interrupt Mode
T
T
T_CRIT set to 80°C
T
INT and T_CRIT_A active low
Pointer set to “00”; Temperature Register
LOW
HIGH
HYST
set to 10°C
set to 64°C
set to 2°C
LOW
then INT would become active. It would stay
HIGH
HIGH
set to 64°C. If T
and T
LOW
+ T
LOW
HYST
to within 4°C of each other
to set the output again.
LOW
is set equal to, or
HYST
HYST
value
set
7
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 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
high, (1).
Therefore, the complete slave address is:
MSB
1
Average Power on Reset Voltage
0
0
vs Temperature
1
0
A1
10013618
www.national.com
LSB
A0
S
for a