Rainbow Electronics LM84 - Manual (Page 9)

Logic Electrical Characteristics
(Continued)
1.0 Functional Description
The LM84 temperature sensor incorporates a band-gap type
temperature sensor using a Local or Remote diode and an
8-bit ADC (Delta-Sigma Analog-to-Digital Converter). The
LM84 is compatible with the serial SMBus and I
2 C inter-
faces. Digital comparators compare Local and Remote read-
ings
to user-programmable setpoints (LT_CRIT and
RT_CRIT). Activation of the T_CRIT_A output indicates that
a temperature reading is greater than the limit preset in a
T_CRIT register.
1.1 T_CRIT_A OUTPUT, T_CRIT LIMITS
T_CRIT_A is activated when the Local temperature reading
is greater than the limit preset in the local critical temperature
setpoint register (LT_CRIT) or when the Remote tempera-
ture reading is greater than the limit preset in the remote
critical temperature setpoint register (RT_CRIT), as shown in
Figure 3. The T_CRIT_A mask bit (bit 7 of the Configuration
Register) when set will disable the T_CRIT_A output.
The Status Register can be read to determine which event
caused the alarm. A bit in the Status Register is set high to
indicate T_CRIT temperature alarm, see
Section 1.8.3.
Local and remote temperature diodes are sampled alter-
nately by the A/D converter. The T_CRIT_A output and the
Status Register flags are updated at the completion of a
conversion, which takes approximately 60 ms. T_CRIT_A
and the Status Register flags are reset only after the Status
Register is read and if the temperature is below the setpoint.
1.2 POWER-ON RESET DEFAULT STATES
LM84 always powers up to these known default states:
1. Local Temperature set to 0˚C
2. Remote Temperature set to 0˚C until the LM84 senses a
diode present or open circuit on the D+ and D− input
pins.
3. Status Register set to 00h.
4. Command Register set to 00h; T_CRIT_A enabled.
5. Local and Remote T_CRIT set to 127˚C
DS100961-5
FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
DS100961-6
FIGURE 3. T_CRIT_A Temperature Response Diagram
LM84
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