ADT7470ARQZ-REEL7

The ADT7470ARQZ-REEL7 is a versatile thermal management controller from Analog Devices that combines multi-channel temperature monitoring with PWM fan control in a single 16-lead QSOP package. Unlike fan controllers with integrated temperature sensors, the ADT7470 is designed to interface with external TMP05 or TMP06 temperature sensors connected in a daisy-chain configuration on a single wire, allowing up to 10 temperature monitoring points distributed throughout a system. This architecture provides significant flexibility in locating temperature sensors at critical hot spots (CPU, GPU, power supplies, hard drives, etc.) without requiring individual ADC channels for each sensor. The TMP05/TMP06 sensors convert temperature into a PWM signal whose duty cycle is proportional to temperature, and the ADT7470 decodes these PWM signals to get temperature readings with 0.0625C resolution. On the fan control side, the ADT7470 provides four independent PWM outputs for driving fan motors and four corresponding tachometer inputs for monitoring fan speed. Each fan can be controlled either manually (direct duty cycle set by register writes) or automatically using a look-up table that maps temperature thresholds to fan speed settings, providing closed-loop thermal control without CPU intervention. All measured values – both temperatures and fan speeds – are continuously compared against user-programmed limit values stored in internal registers. Out-of-limit conditions (over-temperature, fan under-speed, etc.) are flagged in status registers and can generate an SMBALERT interrupt to notify the system controller. The status bits are sticky, meaning they remain set once a fault is detected and must be explicitly cleared by the system controller after reading, ensuring that transient faults are not missed between polling intervals. The device communicates with the host through an I2C/SMBus interface operating at up to 400 kHz, and a three-state address pin allows up to three ADT7470 devices to be used on the same bus for systems requiring more fans or temperature sensors.

The ADT7470 operates as both a temperature sensor hub and a fan controller, with both functions managed by an internal state machine and register set accessible via the I2C/SMBus interface. For temperature monitoring, the device reads PWM-formatted temperature data from daisy-chained TMP05 or TMP06 temperature sensors. When a measurement cycle is initiated (either by writing to the start bit in the configuration register or automatically in continuous measurement mode), the ADT7470 sends a start pulse down the TMP_IN line, which triggers the first TMP05/TMP06 sensor in the chain to begin transmitting its temperature reading as a PWM pulse. Each sensor in the daisy chain transmits its reading sequentially, with the temperature value encoded in the pulse width (the ratio of high time to total period of the PWM signal). The ADT7470 measures this ratio for each sensor in the chain and converts it to a temperature value using the known transfer function of the TMP05/TMP06, storing the results in the temperature registers (0x20 through 0x29 for up to 10 sensors). The highest temperature measured across all sensors is also stored in a dedicated register (0x78) for simplified thermal management algorithms. For fan control, the ADT7470 generates PWM signals on four output pins (PWM1 through PWM4) that drive the fan motors (typically through external MOSFETs or fan drivers, as the outputs are open-drain). The duty cycle of each PWM output determines the fan speed. In manual mode, the duty cycle is set directly by writing to the PWM duty cycle registers. In automatic mode, the duty cycle is determined by a look-up table programmed into the device: the device compares the measured temperature against programmed temperature thresholds and adjusts the fan speed accordingly, providing automatic closed-loop thermal control. To monitor actual fan speed, each tachometer input (TACH1 through TACH4) counts pulses from the fan tachometer output over a defined measurement window, and the resulting count is stored in the TACH measurement registers. These values are compared against minimum speed thresholds to detect stalled or under-speed fans. All out-of-limit conditions (both temperature and fan speed) set corresponding bits in the interrupt status registers and can assert the SMBALERT output if that interrupt source is enabled.

• Server rack and blade server thermal management systems
• Network routers, switches, and telecom equipment cooling control
• Desktop PC and workstation fan control and temperature monitoring
• Industrial PC and embedded computing thermal management
• Data center equipment cooling infrastructure
• Power supply units with thermal monitoring and fan speed control
• RAID controllers and storage systems thermal management
• Medical diagnostic equipment requiring active cooling
• Test and measurement instrumentation thermal control
• Multi-point temperature monitoring with distributed sensors