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ADT7468ARQ Datasheet(PDF) 10 Page - Analog Devices |
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ADT7468ARQ Datasheet(HTML) 10 Page - Analog Devices |
10 / 80 page ADT7468 Rev. 0 | Page 10 of 80 PRODUCT DESCRIPTION The ADT7468 is a complete thermal monitor and multiple fan controller for any system requiring thermal monitoring and cooling. The device communicates with the system via a serial system management bus. The serial bus controller has a serial data line for reading and writing addresses and data (Pin 1), and an input line for the serial clock (Pin 2). All control and programming functions for the ADT7468 are performed over the serial bus. In addition, a pin can be reconfigured as an SMBALERT output to signal out-of-limit conditions. COMPARISON BETWEEN ADT7463 AND ADT7468 The ADT7468 is an upgrade to the ADT7463. The ADT7468 and ADT7463 are almost pin and register map compatible. The ADT7468 and ADT7463 have the following differences: 1. On the ADT7468, the PWM drive signals can be config- ured as either high frequency or low frequency drives. The low frequency option is programmable between 10 Hz and 100 Hz. The high frequency option is 22.5 kHz. On the ADT7463, only the low frequency option is available. 2. Once the VCC is powered up, monitoring of temperature and fan speeds is enabled on the ADT7468 when VCCP is powered up, or if VCCP is never powered up, when the first SMBus transaction with the ADT7468 is completed. On the ADT7463, the STRT bit in Configuration Register 1 must be set to enable monitoring. 3. The fans are switched off by default on power-up on the ADT7468. On the ADT7463, the fans run at full speed on power-up. Fail-safe cooling is provided on the ADT7468 in that, if the measured temperature exceeds the THERM limit (100°C), the fans run at full speed. Fail-safe cooling is also provided 4.6 s after VCCP is powered up. See Figure 48. The fans go to full speed, if the ADT7468 has not been addressed via the SMBus within 4.6 s of when the VCCP is powered up. This protects the system in the event that the SMBus fails. The ADT7468 can be pro- grammed at any time, either before or after the 4.6 s has elapsed, and it behaves as programmed. If VCCP is never powered up, fail-safe cooling is effectively disabled. If VCCP is disabled, writing to the ADT7468 at any time causes the ADT7468 to operate normally. 4. Series resistance cancellation (SRC) is provided on the remote temperature channels on the ADT7468, but not on the ADT7463. SRC automatically cancels linear offset introduced by a series resistance between the thermal diode and the sensor. 5. The ADT7468 has an extended temperature measurement range. The measurement range goes from–64°C to +191°C. On the ADT7463, the measurement range is from −127°C to +127°C. This means that the ADT7468 can measure higher temperatures. The ADT7468 also includes the ADT7463 temperature range; the temperature measure- ment range can be switched by setting Bit 0 of Configuration Register 5. 6. The ADT7468 maximum fan speed (% duty cycle) in the automatic fan speed control loop can be programmed. The maximum fan speed is 100% duty cycle on the ADT7463 and is not programmable. 7. The offset register in the ADT7468 is programmable up to ±64°C with 0.50°C resolution. The offset register of the ADT7463 is programmable up to ±32°C with 0.25°C resolution. 8. VCCP is monitored on Pin 23 of the ADT7468 and can be used to set the threshold for THERM (PROCHOT) (2/3 of VCCP). The threshold for THERM (PROCHOT) is set at VIH = 1.7 V and VIL = 0.8 V on the ADT7463. 9. On the ADT7463, Pin 22 can be reconfigured as SMBus ALERT. This is not available on the ADT7468; instead, SMBALERT can be enabled on Pin 14. 10. A GPIO can also be made available on Pin 14 on the ADT7468. This is not available on the ADT7463. Set the GPIO polarity and direction in Configuration Register 5. The GPIO status bit is Bit 5 of Status Register 2 (shared with TACH4 and THERM, because only one can be enabled at a time). 11. The ADT7463 has three possible SMBus addresses, which are selectable using the address select and address enable pins. The ADT7468 has one SMBus address available at Address 0x2E. Due to the inclusion of extra functionality, the register map has changed, including an additional configuration register: Configuration Register 5 at Address 0x7C. Configuration Register 5 Bit 0: If Bit 0 is set to 1, the ADT7468 is backward compatible temperature-wise with the ADT7463. Measurements, TMIN calibration circuit, fan control, etc., work in the range −127°C to +127°C. Also, care should be taken in reprogramming the temperature limits (TMIN, operating point, THERM limits) to their desired twos complement value, because the power-on default for them is at Offset 64. The extended temperature range is −64°C to 191°C. The default is 1, which is in the −64°C to +191°C temperature range. |
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