MIC184 Ver la hoja de datos (PDF) - Micrel
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componentes Descripción
Fabricante
MIC184 Datasheet PDF : 20 Pages
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MIC184
Inputs
A 2/T 1 A 1 A 0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
diode 0
0
diode 0
1
diode 1
0
diode 1
1
MIC 184 S lave Addres s
B inary
Hex
100 1000b
48h
100 1001b
49h
100 1010b
4Ah
100 1011b
4B h
100 1100b
4C h
100 1101b
4Dh
100 1110b
4E h
100 1111b
4F h
100 1000b
48h
100 1001b
49h
100 1010b
4Ah
100 1011b
4B 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
Micrel
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 VDD 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 1110b). An interrupt
will be generated if so enabled. The temperature reported for
the external zone will remain 0 1111 1111b = +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
May 2006
C ommand_B yte
B inary
Hex
0000 0000b
00h
0000 0001b
01h
0000 0010b
02h
0000 0011b
03h
0000 0100b
04h
·
·
·
·
·
·
L abel
TE MP
C ONFIG
T_HYS T
T_S E T
T arget R egis ter
Des c ription
meas ured temperature res ult
configuration regis ter
temperature hys teres is
overtemperature s etpoint
res erved
do not us e
1111 1111b
FFh
Table 2. MIC184 Register Addresses
7
MIC184
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