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ADT7461ARZ-REEL Datasheet(PDF) 10 Page - ON Semiconductor |
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ADT7461ARZ-REEL Datasheet(HTML) 10 Page - ON Semiconductor |
10 / 20 page ADT7461 http://onsemi.com 10 Conversion Rate Register The conversion rate register is Address 0x04 at read and Address 0x0A at write. The lowest four bits of this register are used to program the conversion rate by dividing the internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 to give conversion times from 15.5 ms (Code 0x0A) to 16 seconds (Code 0x00). For example, a conversion rate of 8 conversions per second means that beginning at 125 ms intervals; the device performs a conversion on the internal and external temperature channels. This register can be written to and read back over the SMBus. The higher four bits of this register are unused and must be set to 0. The default value of this register is 0x08, giving a rate of 16 conversions per second. Use of slower conversion times greatly reduces the device power consumption, as shown in Table 9. Table 9. CONVERSION RATE REGISTER CODES Code Conversion/ Sec Average Supply Current mA Typ at VDD = 5.5 V 0x00 0.0625 121.33 0x01 0.125 128.54 0x02 0.25 131.59 0x03 0.5 146.15 0x04 1 169.14 0x05 2 233.12 0x06 4 347.42 0x07 8 638.07 0x08 16 252.44 0x09 32 417.58 0x0A 64 816.87 0x0B to 0xFF Reserved Limit Registers The ADT7461 has eight limit registers: high, low, and THERM temperature limits for both local and remote temperature measurements. The remote temperature high and low limits span two registers each to contain an upper and lower byte for each limit. There is also a THERM hysteresis register. All limit registers can be written to and read back over the SMBus. See Table 13 for address details of the limit registers and their power-on default values. When Pin 6 is configured as an ALERT output, the high limit registers perform a > comparison while the low limit registers perform a ≤ comparison. For example, if the high limit register is programmed with 80 °C, then measuring 81 °C results in an out-of-limit condition, setting a flag in the status register. If the low limit register is programmed with 0 °C, measuring 0°C or lower results in an out-of-limit condition. Exceeding either the local or remote THERM limit asserts THERM low. When Pin 6 is configured as THERM2, exceeding either the local or remote high limit asserts THERM2 low. A default hysteresis value of 10 °C is provided that applies to both THERM channels. This hysteresis value may be reprogrammed to any value after powerup (Register Address 0x21). It is important to remember that the temperature limits data format is the same as the temperature measurement data format. So, if the temperature measurement uses default binary, the temperature limits also use the binary scale. If the temperature measurement scale is switched, however, the temperature limits do not switch automatically. The user must reprogram the limit registers to the desired value in the correct data format. For example, if the remote low limit is set at 10 °C and the default binary scale is being used, the limit register value should be 0000 1010b. If the scale is switched to offset binary, the value in the low temperature limit register should be reprogrammed to be 0100 1010b. Status Register The status register is a read-only register at Address 0x02. It contains status information for the ADT7461. Bit 7 of the status register indicates the ADC is busy converting when it is high. The other bits in this register flag the out-of-limit temperature measurements (Bits 6 to 3 and Bits 1 to 0) and the remote sensor open circuit (Bit 2). If Pin 6 is configured as an ALERT output, the following applies. If the local temperature measurement exceeds its limits, Bit 6 (high limit) or Bit 5 (low limit) of the status register asserts to flag this condition. If the remote temperature measurement exceeds its limits, then Bit 4 (high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to flag an open-circuit condition on the remote sensor. These five flags are NOR’d together so if any of them is high, the ALERT interrupt latch is set and the ALERT output goes low. Reading the status register clears the five flags, Bits 6 to 2, provided the error conditions causing the flags to be set have gone away. A flag bit can be reset only if the corresponding value register contains an in-limit measurement or if the sensor is good. The ALERT interrupt latch is not reset by reading the status register. It resets when the ALERT output has been serviced by the master reading the device address, provided the error condition has gone away and the status register flag bits are reset. When Flag 1 and/or Flag 0 are set, the THERM output goes low to indicate the temperature measurements are outside the programmed limits. The THERM output does not need to be reset, unlike the ALERT output. Once the measurements are within the limits, the corresponding status register bits are reset automatically and the THERM output goes high. The user may add hysteresis by programming Register 0x21. The THERM output is reset only when the temperature falls to limit value minus hysteresis value. |
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