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MIC284-0BMM Datasheet(PDF) 11 Page - Micrel Semiconductor |
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MIC284-0BMM Datasheet(HTML) 11 Page - Micrel Semiconductor |
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11 / 20 page  September 29, 2000 11 MIC284 MIC284 Micrel e r u t a r e p m e Ty r a n i Bx e H C ° 5 2 1 +1 0 1 1 1 1 1 0 b D 7 h C ° 5 2 +1 0 0 1 1 0 0 0 b 9 1 h C ° 0 . 1 +1 0 0 0 0 0 0 0 b 1 0 h C ° 00 0 0 0 0 0 0 0 b 0 0 h C ° 0 . 1 – 1 1 1 1 1 1 1 1 b F F h C ° 5 2 – 1 1 1 0 0 1 1 1 b 7 E h C ° 0 4 – 0 0 0 1 1 0 1 1 b 8 D h C ° 5 5 – 1 0 0 1 0 0 1 1 b 9 C h Table 3. Digital Temperature Format 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 MIC284 for temperatures. A/D Converter Timing Whenever the MIC284 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 MIC284. When the part is accessed, the conversion in progress will be halted, and the partial result discarded. When the access to the MIC284 is complete, the ADC will begin a new conversion cycle with results for the remote zone valid t CONV1 after that, and for the local zone t CONV0 later. Figure 4 shows this behavior. The conversion time is twice as long for external conversions as it is for internal conversions. This allows the use of a filter capacitor on T1 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 acquiring temperature data starting with the external zone (zone 1), followed by the internal zone (zone 0). If the ADC is 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 MIC284 is shut down, powered off, or is interrupted by a serial bus transaction as described above. Power-On When power is initially applied, the MIC284’s internal regis- ters are set to their default states, and A0 is read to establish the device’s slave address. The MIC284’s power-up default state can be summarized as follows: • Normal Mode operation (i.e., part is not in shut- down) • /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 • CRIT1 = 97 °C; nCRIT1 = 92°C • Initialized to recognize overtemperature faults 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 either of the TEMPx registers, exceeds the threshold pro- grammed 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 bits will remain high unless and until the measured temperature 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 (Sx) to be set, and the /INT output to be asserted, they will not be automatically de-asserted when the mea- sured temperature falls below T_HYSTx. They can only be de-asserted by reading any of the MIC284’s internal registers or by putting the device into shutdown mode. If the most recent temperature 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 condition, 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 MIC284 back- ward compatible with that of the LM75 and similar devices. In both modes, the MIC284 will be responsive to over-tempera- ture 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 MIC284’s power consumption drops to 1 µA 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. |
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