MIC280_14 Datasheet, PDF (10/28 Pages) Micrel Semiconductor – Precision IttyBitty™ Thermal Supervisor

Micrel, Inc.
Alert Response Address
In addition to the Read_Byte, Write_Byte, and
Read_Word protocols, the MIC280 adheres to the
SMBus protocol for response to the Alert Response
Address (ARA). The MIC280 expects to be interrogated
using the ARA when it has as- serted its /INT output.
Temperature Data Format
The least-significant bit of each temperature register
(high bytes) 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 used by the MIC280
for temperatures.
Table 3. Digital Temperature Format, High Bytes
Temperature
Binary
Hex
+127°C
0111 1111
7F
+125°C
0111 1101
7D
+25°C
0001 1001
19
+1°C
0000 0001
01
0°C
0000 0000
00
–1°C
1111 1111
FF
–25°C
1110 0111
E7
–125°C
1000 0011
83
–128°C
1000 0000
80
Extended temperature resolution is provided for the
external zone. The high and low temperature limits and
the measured temperature for zone one are reported as
12-bit values stored in a pair of 8-bit registers. The
measured temperature, for example, is reported in
registers TEMP1h, the high-order byte, and TEMP1l, the
low-order byte. The values in the low-order bytes are left-
justified four-bit binary values representing one-sixteenth
degree increments.
MIC280
The A-D converter resolution for zone 1 is selectable
from nine to twelve bits via the configuration register.
Low-order bits beyond the resolution selected will be
reported as zeroes. Examples of this format are shown in
Table 5.
Fault Queue
A set of fault queues (programmable digital filters) are
provided in the MIC280 to prevent false tripping due to
thermal or electrical noise. Two bits, CONFIG[5:4], set
the depth of the fault queues. The fault queue setting
then determines the number of consecutive temperature
events (TEMPx > THIGHx or TEMPx < TLOWx) which
must occur in order for the condition to be considered
valid. As an example, assume CONFIG[5:4] is
programmed with 10b. The measured temperature for a
given zone would have to exceed THIGHx for four
consecutive A/D conversions before /INT would be
asserted or the status bit set.
Like any filter, the fault queue function also has the effect
of delaying the detection of temperature events. In this
example, it would take 4 × t_CONV to detect a temperature
event. The fault queue depth versus CONFIG[5:4] of the
configuration register is shown in Table 4. Note: there is
no fault queue for overtemperature events (CRIT0 and
CRIT1) or diode faults. The fault queue applies only to
high-temperature and low-temperature events as
determined by the THIGHx and TLOWx registers. Any
write to CONFIG will result in the fault queues being
purged and reset. Writes to any of the limit registers,
TLOWx or THIGHx, will result in the fault queue for the
corresponding zone being purged and reset.
Table 4. Fault Queue Depth Settings
CONFIG[5:4]
Fault Queue Depth
00
1 (Default)
01
2
10
4
11
6
May 5, 2014
10
Revision 2.0