MIC284
Temperature Data Format
The LSB of each register represents one degree Centigrade.
The values are in a two’s complement format, wherein the
most significant bit (D7), represents the sign: zero for posi-
tive temperatures and one for negative temperatures. Table
3 shows examples of the data format used by the MIC284
for temperatures.
A/D Converter Timing
Whenever the MIC284 is not in its low power shutdown mode,
the internal A/D converter (ADC) attempts to make continuous
conversions unless interrupted by a bus transaction accessing
the MIC284. When the part is accessed, the conversion in
progress will be halted, and the partial result discarded. When
the access to the MIC284 is complete, the ADC will begin a
new conversion cycle with results for the remote zone valid
t
CONV1
after that, and for the local zone t
CONV0
later. Figure
4 shows this behavior. The conversion time is twice as long
for external conversions as it is for internal conversions. This
allows the use of a filter capacitor on T1 without a loss of
accuracy due to the resulting longer settling times.
Upon powering-up, coming out of shutdown mode, or resum-
ing operation following a serial bus transaction, the ADC will
begin acquiring temperature data starting with the external
zone (zone 1), followed by the internal zone (zone 0). If the
ADC is interrupted by a serial bus transaction, it will restart
the conversion that was interrupted and then continue in the
normal sequence. This sequence will repeat indefinitely until
the MIC284 is shut down, powered off, or is interrupted by a
serial bus transaction as described above.
Power-On
When power is initially applied, the MIC284’s internal registers
are set to their default states, and A0 is read to establish
the device’s slave address. The MIC284’s power-up default
state can be summarized as follows:
• Normal Mode operation (i.e., part is not in shut-
down)
• /INT function is set to Comparator Mode
• Fault Queue depth = 1 (FQ=00)
• Interrupts are enabled (IM = 0)
• T_SET0 = 81°C; T_HYST0 = 76°C
• T_SET1 = 97°C; T_HYST1 = 92°C
• CRIT1 = 97°C; nCRIT1 = 92°C
• Initialized to recognize overtemperature faults
Comparator and Interrupt Modes
Micrel, Inc.
Depending on the setting of the MODE bit in the configura-
tion register, the /INT output will behave either as an interrupt
request signal or a thermostatic control signal. Thermostatic
operation is known as
comparator mode.
The /INT output
is asserted when the measured temperature, as reported
in either of the TEMPx registers, exceeds the threshold
programmed into the corresponding T_SETx register for the
number of conversions specified by Fault_Queue (described
below). In comparator mode, /INT will remain asserted and
the status bits will remain high unless and until the measured
temperature falls below the value in the T_HYSTx register
for Fault_Queue conversions. No action on the part of the
host is required for operation in comparator mode. Note that
entering shutdown mode will not affect the state of /INT when
the device is in comparator mode.
In
interrupt mode,
once a temperature event has caused a
status bit (Sx) to be set, and the /INT output to be asserted,
they will not be automatically de-asserted when the measured
temperature falls below T_HYSTx. They can only be de-as-
serted by reading any of the MIC284’s internal registers or
by putting the device into shutdown mode. If the most recent
temperature event was an overtemperature condition, Sx will
not be set again, and /INT cannot be reasserted, until the
device has detected that TEMPx < T_HYSTx. Similarly, if
the most recent temperature event was an undertemperature
condition, Sx will not be set again, and /INT cannot be reas-
serted, until the device has detected that TEMPx > T_SETx.
This keeps the internal logic of the MIC284 backward compat-
ible with that of the LM75 and similar devices. In both modes,
the MIC284 will be responsive to over-temperature events at
power-up. See "Interrupt Generation", below.
Shutdown Mode
Setting the SHDN bit in the configuration register halts the
otherwise continuous conversions by the A/D converter. The
MIC284’s power consumption drops to 1µA typical in shutdown
mode. All registers may be read from or written to while in
shutdown mode. Serial bus activity will slightly increase the
part’s power consumption.
Entering shutdown mode will not affect the state of /INT
when the device is in comparator mode (MODE = 0). It will
retain its state until after the device exits shutdown mode and
resumes A/D conversions.
If the device is shut down while in interrupt mode (mode =
Temperature
+125° C
+25° C
+1.0° C
0° C
– 1.0° C
– 25° C
– 40° C
– 55° C
Binar y
0111 1101
b
0001 1001
b
0000 0001
b
0000 000 0
b
1111 111 1
b
1110 011 1
b
1101 100 0
b
1100 100 1
b
He x
7D
h
19
h
01
h
00
h
FF
h
E7
h
D8
h
C9
h
September 2005
Table 3. Digital Temperature Format
11
MIC284
MICREL [ MICREL SEMICONDUCTOR ]
