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MAX6642ATT9E-T Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX6642ATT9E-T Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 14 page tion rules apply, and the device with the lower address code wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until cleared. (The conditions for clearing an ALERT vary depending on the type of slave device.) Successful completion of the alert response protocol clears the interrupt latch. If the condition still exists, the device reasserts the ALERT interrupt at the end of the next conversion. Command Byte Functions The 8-bit command byte register (Table 3) is the master index that points to the various other registers within the MAX6642. The register’s POR state is 0000 0000, so a Receive Byte transmission (a protocol that lacks the command byte) that occurs immediately after POR returns the current local temperature data. Single-Shot The single-shot command immediately forces a new conversion cycle to begin. If the single-shot command is received while the MAX6642 is in standby mode (RUN bit = 1), a new conversion begins, after which the device returns to standby mode. If a single-shot con- version is in progress when a single-shot command is received, the command is ignored. If a single-shot command is received in autonomous mode (RUN bit = 0), the command is ignored. Configuration Byte Functions The configuration byte register (Table 4) is a read-write register with several functions. Bit 7 is used to mask (disable) interrupts. Bit 6 puts the MAX6642 into stand- by mode (STOP) or autonomous (RUN) mode. Bit 5 dis- ables local temperature conversions for faster (8Hz) remote temperature monitoring. Bit 4 prevents setting the ALERT output until two consecutive measurements result in fault conditions. Status Byte Functions The status byte register (Table 5) indicates which (if any) temperature thresholds have been exceeded. This byte also indicates whether the ADC is converting and whether there is an open-circuit fault detected on the external sense junction. After POR, the normal state of all flag bits is zero, assuming no alarm conditions are present. The status byte is cleared by any successful read of the status byte after the overtemperature fault condition no longer exists. Slave Addresses The MAX6642 has eight fixed addresses available. These are shown in Table 6. The MAX6642 also responds to the SMBus alert response slave address (see the Alert Response Address section). POR and UVLO To prevent ambiguous power-supply conditions from corrupting the data in memory and causing erratic behavior, a POR voltage detector monitors VCC and clears the memory if VCC falls below 2.1 (typ). When power is first applied and VCC rises above 2.1 (typ), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC undervoltage lockout (UVLO) comparator prevents the ADC from converting until there is sufficient headroom (VCC = +2.7V typ). Power-Up Defaults Power-up defaults include: • ALERT output is cleared. • ADC begins autoconverting at a 4Hz rate. • Command byte is set to 00h to facilitate quick local Receive Byte queries. • Local (internal) THIGH limit set to +70°C. • Remote (external) THIGH limit set to +120°C. Applications Information Remote-Diode Selection The MAX6642 can directly measure the die temperature of CPUs and other ICs that have on-board temperature- sensing diodes (see the Typical Operating Circuit) or they can measure the temperature of a discrete diode- connected transistor. Effect of Ideality Factor The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote “diode” (actually a transistor). The MAX6642 is optimized for n = 1.008, which is the typical value for the Intel Pentium ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm _______________________________________________________________________________________ 9 PART NO. SUFFIX ADDRESS MAX6642ATT90 1001 000 MAX6642ATT92 1001 001 MAX6642ATT94 1001 010 MAX6642ATT96 1001 011 MAX6642ATT98 1001 100 MAX6642ATT9A 1001 101 MAX6642ATT9C 1001 110 MAX6642ATT9E 1001 111 Table 6. Slave Address |
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