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MIC284 Datasheet(PDF) 7 Page - Micrel Semiconductor |
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MIC284 Datasheet(HTML) 7 Page - Micrel Semiconductor |
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7 / 20 page  September 2005 7 MIC284 MIC284 Micrel, Inc. mask bit. /CRIT: Over-temperature events are indicated to external circuitry via this output. This output is open-drain and may be wire-OR’ed with other open-drain signals. Most systems will require a pull-up resistor or current source on this pin. T1:Thispinconnectstoanoff-chipPNdiodejunction,for monitoringthejunctiontemperatureataremotelocation. The remote diode may be an embedded thermal sens- ing junction in an integrated circuit so equipped (such as Intel's Pentium III), or a discrete 2N3906-type bipolar transistor with base and collector tied together. Temperature Measurement Thetemperature-to-digitalconverterisbuiltaroundaswitched current source and an eight-bit analog-to-digital converter. Each diode's temperature is calculated by measuring its for- ward voltage drop at two different current levels. An internal multiplexerdirectstheMIC284'scurrentsourceoutputtoeither aninternalorexternaldiodejunction. TheMIC284usestwo’s- complement data to represent temperatures. If the MSB of a temperature value is zero, the temperature is zero or positive. If the MSB is one, the temperature is negative. More detail on this is given in the "Temperature Data Format" section below. A “temperature event” results if the value in either of the temperature result registers (TEMPx) becomes greater than the value in the corresponding temperature setpoint register (T_SETx). Another temperature event occurs if and when the measured temperature subsequently falls below the temperature hysteresis setting in T_HYSTx. During normal operation the MIC284 continuously performs temperature-to-digital conversions, compares the results against the setpoint registers, and updates the states of /INT, /CRIT, and the status bits accordingly. The remote zone is converted first, followed by the local zone. The states of /INT, /CRIT, and the status bits are updated after each measure- ment is taken. The remote diode junction connected to T1 may be embedded in an integrated circuit such as a CPU, ASIC, or graphics processor, or it may be a diode-connected discrete transistor. Diode Faults The MIC284 is designed to respond in a failsafe manner to hardware faults in the external sensing circuitry. If the con- nection to the external diode is lost or the sense line (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°C). This will cause a temperature event to occur if T_SET1 or CRIT1 are set to any value less than 127°C (7Fh = 0111 1111b). An interrupt will be generated on /INT if so enabled. The temperature reported for the external zone will remain +127°C until the fault condition is cleared. This fault detection mechanism requires that the MIC284 complete the number of conversion cycles specified by Fault_Queue. The part will therefore require one or more conversion cycles following power-on or a transition from shutdown to normal operation before reporting an external diode fault. Serial Port Operation TheMIC284usesstandardSMBusWrite_ByteandRead_Byte operations for communication with its host. The SMBus Write_Byte operation involves sending the device’s slave address (with the R/W bit low to signal a write operation), followed by a command byte and a data byte. 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 MIC284, 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 the part may then be clocked out. The command byte is eight bits wide. This byte carries the address of the MIC284 register to be operated upon, and is stored in the part’s pointer register. The pointer register is an internal write-only register. The command byte (pointer register) values corresponding to the various MIC284 register addresses are shown inTable 2. Command byte values other than those explicitly shown are reserved, and should not be used. Any command byte sent to the MIC284 will persist in the pointer register indefinitely until it is overwritten by another command byte. If the location latched in the pointer register from the last operation is known to be correct (i.e., points to the desired register), then the Receive_Byte procedure may be used. To perform a Receive_Byte, the host sends an address byte to select the MIC284, and then retrieves the data byte. Figures 1 through 3 show the formats for these procedures. |
Similar Part No. - MIC284_05 |
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Similar Description - MIC284_05 |
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