Datasheet ADT7470 (Analog Devices) - 7

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Data Sheet ADT7470 FUNCTIONAL DESCRIPTION GENERAL DESCRIPTION
sensor (approximately 120 ms) and on the number of TMP05s daisy-chained together. The total monitoring cycle time is the The ADT7470 is a multichannel, pulse-width modulation temperature conversion time multiplied by the number of (PWM) fan controller and monitor for any system requiring temperature channels being monitored. monitoring and cooling. The device communicates with the system via a serial system management bus. The device has Fan tach measurements are taken in paral el and are not syn- a single address line for address selection (Pin 11), a serial chronized with the temperature measurements in any way data line for reading and writing addresses and data (Pin 16),
CONFIGURATION REGISTER 1 (ADDRESS 0X40)
and an input line for the serial clock (Pin 1). All control and This register contains the STRT bit, Bit 0, which begins the programming functions of the ADT7470 are performed over monitoring cycle on the ADT7470. the serial bus, which supports both SMBus and fast I2C speci- fications. In addition, an SMBALERT interrupt output is The SMBus timeout can be disabled , fast tach enabled, and provided to indicate out-of-limit conditions. the registers locked, by writing to this register. When the ADT7470 monitoring sequence is started, it cycles Control of high or low frequency fan drive, and the config- through each fan tach input to measure fan speed. Measured uration for Pin 13, can be accessed via this register. values from these inputs are stored in value registers. These See Table 31 for more details. can be read out over the serial bus, or they can be automatical y
CONFIGURATION REGISTER 2 (ADDRESS 0X74)
compared with programmed limits stored in the limit registers. The results of out-of-limit comparisons are stored in the status Writing a 1 to Bit 0 in this register puts the ADT7470 in registers, which can be read over the serial bus to flag out-of- shutdown mode, which puts the part into a low current limit conditions. If fan speeds drop below preset levels or a consumption mode. fan stalls, an interrupt is generated. Likewise, the ADT7470 The PWM frequency for each fan is control ed via this register. can flag fan over speed conditions by using limits set in the Fan speed measurement can be disabled for each fan by writing fan tach maximum registers. to this register.
ADT7470 Monitoring Cycle
See Table 44 for more details. The monitoring cycle begins when a 1 is written to the start
ID REGISTERS
bit (Bit 0) of Configuration Register 1 (Register 0x40). Each fan tach input is monitored in turn, and, as each measurement The ADT7470 has three read-only registers for identifying is completed, the result is automatically stored in the appropri- the part and silicon revision. ate value register. Multiple temperature channels can also be The device ID register is located at address 0x3D, and is set monitored by clocking in temperatures using the TMP_IN to 0x70. pin. The temperature measurement function is addressed The company ID register, located at address 0x3E, is set to 0x41. in hardware and requires no software intervention. The monitoring cycle continues unless disabled by writing a 0 The revision number register is at address 0x3F, and contains to Bit 7 of Configuration Register 1. the revision number of the ADT7470 silicon. The rate of temperature measurement updates depends on the nominal conversion rate of the TMP05/TMP06 temperature Rev. E | Page 7 of 40 Document Outline Features Applications General Description Functional Block Diagram Revision History Specifications Serial Bus Timing Specifications Absolute Maximum Ratings Thermal Characteristics ESD Caution Pin Configuration and Function Descriptions Functional Description General Description ADT7470 Monitoring Cycle Configuration Register 1 (Address 0x40) Configuration Register 2 (Address 0x74) ID Registers General-Purpose I/O Pins (Open Drain) SMBus/I2C Serial Interface Address Selection Serial Bus Protocol Write Operations Send Byte Write Byte Read Operations Receive Byte Alert Response Address SMBus Timeout Temperature Measurement Using TMP05/TMP06 Measuring Temperature TMP05/TMP06 Decoder Temperature ReadBack By the Host Temperature Data Format Temperature Measurement Limits Thermal Zones for Automatic Fan Control Thermal Zone TMIN Limit and Status Registers Limit Values Temperature Limits Fan Speed Limits Out-of-Limit Comparisons Status Registers SMBALERT Interrupt Handling SMBALERT Interrupts Masking Interrupt Sources Enabling the SMBALERT Interrupt Output Fan Drive Using PWM Control High Frequency Fan Drive Low Frequency Fan Drive Setting the Fan Drive Frequency Inverted PWM Output Fan Full Speed Function Fan Speed Measurement Tach Inputs Pulse Stretching Disabling Tach measurement Fan Speed Measurement Fan Speed Measurement Registers Reading Fan Speed from the ADT7470 Fan Tach Limit Registers Fan Speed Measurement Rate Calculating Fan Speed and Tachometer Limits Fan Pulses per Revolution Manual Fan Speed Control Setting the PWM Duty Cycle Example 1: For a PWM Duty Cycle of 50% Example 2: For a PWM Duty Cycle of 33% Automatic Fan Speed Control PWM Min Duty Cycle Example: For a PWM Min Duty Cycle of 30% PWN Max Duty Cycle PWM Current Duty Cycle Register Map Detailed Register Descriptions Outline Dimensions Ordering Guide