MIC384 Micrel Semiconductor, MIC384 Datasheet - Page 10

• Manufacturer Part Number: MIC384
• Description: Three-Zone Thermal Supervisor Advance Information
• Manufacturer: Micrel Semiconductor

MIC384
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 positive
temperatures and one for negative temperatures. Table 3
shows examples of the data format used by the MIC384 for
temperatures.
A/D Converter Timing
Whenever the MIC384 is not in its low power shutdown mode,
the internal A/D converter (ADC) attempts to make continu-
ous conversions unless interrupted by a bus transaction
accessing the MIC384.
Upon powering up or coming out of shutdown mode, the ADC
will begin acquiring temperature data starting with the first
external zone, zone 1, then the second external zone, zone
2, and finally the internal zone, zone 0. Results for zone 1 will
be valid after t
another t
shows this behavior. The conversion time is twice as long for
external conversions as it is for internal conversions. This
allws the use of a filter capacitor on T1 and/or T2 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 aquiring temperature data with the first external zone
(zone 1), followed by the second external zone (zone 2), and
then the internal zone (zone 0). If the ADC in 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 MIC384 is shut
down, powered off, or is interrupted by a serial bus transac-
tion as described above.
Power On
When power is initially applied, the MIC384’s internal regis-
ters are set to their default states. Also at this time, the level
on the address input, A0, is read to establish the device’s
slave address. The MIC384’s power-up default state can be
summarized as follows:
MIC384
• Normal mode operation (i.e., part is not in
• /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
• T_SET2 = 97 C; T_HYST2 = 92 C
• Initialized to recognize overtemperature faults
shutdown)
CONV1
CONV1
, and for the local zone t
, results for zone two will be ready after
CONV0
later. Figure 4
10
Comparator and Interrupt Modes
Depending on the setting of the MODE bit in the configuration
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 any
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
bit(s) will remain high unless and until the measured tempera-
ture 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 to be set and the /INT output to be asserted, they will
not be automatically de-asserted when the measured tem-
perature falls below T_HYSTx. They can only be de-asserted
by reading any of the MIC384’s internal registers or by putting
the device into shutdown mode. If the most recent tempera-
ture 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 condi-
tion, Sx will not be set again, and /INT cannot be reasserted,
until the device has detected that TEMPx > T_SETx. This
keeps the internal logic of the MIC384 backward compatible
with that of the LM75 and similar devices. In both modes, the
MIC384 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
MIC384’s power consumption drops to 1 A typical in shut-
down 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.
However, if the device is shut down while in interrupt mode,
the /INT pin will be unconditionally de-asserted and the
internal latches holding the interrupt status will be cleared.
Therefore, no interrupts will be generated while the MIC384
September 2000
Micrel