May 2006 7 MIC184
MIC184 Micrel
stupnI sserddAevalS481CIM
1T/2A 1A 0A yraniB xeH
0 0 0
0001001
b
84
h
0 0 1 1001001
b
94
h
0 1 0 0101001
b
A4
h
0 1 1 1101001
b
B4
h
1 0 0 0011001
b
C4
h
1 0 1 1011001
b
D4
h
1 1 0 0111001
b
E4
h
1 1 1 1111001
b
F4
h
edoid 0 0 0001001
b
84
h
edoid 0 1 1001001
b
94
h
edoid 1 0 0101001
b
A4
h
edoid 1 1 1101001
b
B4
h
Table 1. MIC184 Slave Address Settings
Temperature Measurement
The temperature-to-digital converter for both internal and
external temperature data is built around a switched current
source and a 9-bit analog-to-digital converter. The tem-
perature is calculated by measuring the forward voltage of a
diode junction at two different bias current levels. An internal
multiplexer directs the current source’s output to either an
internal or external diode junction.
The MIC184 uses two’s-complement data to represent
temperatures. If the MSB of a temperature value is 0, the
temperature is ≥ 0°C. If the MSB is 1, the temperature is <
0°. More detail on this is given in “Temperature Data For-
mat” below. A temperature event results if the value in the
temperature result register (TEMP) is greater than the value
in the overtemperature setpoint register (T_SET), or if it is
less than the value in the temperature hysteresis register
(T_HYST).
The value of the ZONE bit in the configuration register deter-
mines whether readings are taken from the on-chip sensor
or from the A2/T1 input. At power-up, the ZONE bit of the
configuration register is set to zero. The MIC184 therefore
monitors its internal temperature and compares the result
against the contents of T_SET and T_HYST. Setting the ZONE
bit in CONFIG will result in the MIC184 acquiring temperature
data from an external diode connected to the A2/T1 pin. This
diode may be embedded in an integrated circuit (such as a
CPU, ASIC, or graphics processor), or it may be a diode-con-
nected discrete transistor. Once the new value is written to
CONFIG, the A/D converter will begin a new conversion and
return temperature data from the external zone. This data
will be compared against T_SET, T_HYST, and the state of
the Fault_Queue (described below). The internal status bit
(STS) and the INT output will then be updated accordingly.
See “Applications Information” for more details on switching
between zones.
Diode Faults
The MIC184 is designed to respond in a fail-safe manner to
hardware faults in the external sensing circuitry. If the con-
nection to the external diode is lost, or the sense line (A2/T1)
is shorted to V
DD
or ground, the temperature data reported
by the A/D converter will be forced to its full-scale value
(+127.5°C). This will cause an overtemperature event to oc-
cur whenever T_SET ≤ +127.0°C (0 1111 1110
b
). An interrupt
will be generated if so enabled. The temperature reported for
the external zone will remain 0 1111 1111
b
= +127.5°C until
the fault condition is cleared. This fault detection requires
that the MIC184 complete the number of conversion cycles
specified by Fault_Queue. The MIC184 may therefore require
one or more conversion cycles following power-on or a transi-
tion from shutdown to normal operation before reporting an
external diode fault.
Serial Port Operation
The MIC184 uses standard SMBus WRITE_BYTE, READ_
BYTE, WRITE_WORD, and READ_WORD operations for
communication with its host. The SMBus WRITE_BYTE and
WRITE_WORD operations involve sending the device’s slave
address (with the R/W bit low to signal a write operation),
followed by a command byte and one or two data bytes. The
SMBus READ_BYTE operation is similar, but is a composite
write and read operation: the host first sends the device’s
slave address followed by the command byte, as in a write
operation. A new “start” bit must then be sent to the MIC184,
followed by a repeat of the slave address with the R/W bit
(LSB) set to the high (read) state. The data to be read from
etyB_dnammoC retsigeRtegraT
yraniB xeH lebaL noitpircseD
00000000
b
00
h
PMET tlusererutarepmetderusaem
10000000
b
10
h
GIFNOC retsigernoitarugifnoc
01000000
b
20
h
TSYH_T siseretsyherutarepmet
11000000
b
30
h
TES_T tniopteserutarepmetrevo
00100000
b
40
h
devreser esutonod
·
·
·
·
·
·
11111111
b
FF
h
Table 2. MIC184 Register Addresses
