Analog Devices dBCool ADT7468 Instruction Manual
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Analog Devices dBCool ADT7468 Instruction Manual

Analog Devices dBCool ADT7468 Instruction Manual

Remote thermal controller and voltage monitor
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FEATURES
Monitors up to 5 voltages
Controls and monitors up to 4 fans
High and low frequency fan drive signal
1 on-chip and 2 remote temperature sensors
Series resistance cancellation on the remote channel
Extended temperature measurement range, up to 191°C
Dynamic T
control mode intelligently optimizes system
MIN
acoustics
Automatic fan speed control mode manages system
cooling based on measured temperature
Enhanced acoustic mode dramatically reduces user
perception of changing fan speeds
Thermal protection feature via THERM output
Monitors performance impact of Intel® Pentium
Thermal control circuit via THERM input
2-wire, 3-wire, and 4-wire fan speed measurement
Limit comparison of all monitored values
Meets SMBus 2.0 electrical specifications
(fully SMBus 1.1-compliant)
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
®
4 processor
FUNCTIONAL BLOCK DIAGRAM
VID5
VID4
ACOUSTIC
VID3
ENHANCEMENT
VID2
CONTROL
VID1
VID0
ACOUSTIC
PWM1
PWM REGISTERS
ENHANCEMENT
AND
PWM2
CONTROL
CONTROLLERS
HF & LF
PWM3
TACH1
TACH2
FAN SPEED
COUNTER
TACH3
TACH4
PERFORMANCE
MONITORING
THERMAL
THERM
PROTECTION
V
TO ADT7468
CC
V
CC
D1+
D1–
SRC
D2+
D2–
INPUT
SIGNAL
+5V
IN
CONDITIONING
+12V
IN
AND
+2.5V
ANALOG
IN
MULTIPLEXER
V
CCP
BAND GAP
TEMP SENSOR
捷多邦，专业PCB打样工厂，24小时加急出货
dBCool
Controller and Voltage Monitor
GENERAL DESCRIPTION
The ADT7468 dBCool controller is a thermal monitor and
multiple PWM fan controller for noise sensitive or power
sensitive applications requiring active system cooling. The
ADT7468 can drive a fan using either a low or high frequency
drive signal, monitor the temperature of up to two remote
sensor diodes plus its own internal temperature, and measure
and control the speed of up to four fans, so that they operate at
the lowest possible speed for minimum acoustic noise.
The automatic fan speed control loop optimizes fan speed for a
given temperature. A unique, dynamic T
enables the system thermals/acoustics to be intelligently
managed. The effectiveness of the system's thermal solution can
be monitored using the THERM input. The ADT7468 also
provides critical thermal protection to the system using the
bidirectional THERM pin as an output to prevent system or
component overheating.
SCL SDA
SMBALERT
SERIAL BUS
INTERFACE
ADDRESS
AUTOMATIC
POINTER
FAN SPEED
REGISTER
CONTROL
PWM
DYNAMIC
CONFIGURATION
T
MIN
REGISTERS
CONTROL
INTERRUPT
MASKING
INTERRUPT
STATUS
REGISTERS
ADT7468
LIMIT
10-BIT
COMPARATORS
ADC
VALUE AND
LIMIT
BAND GAP
REGISTERS
REFERENCE
GND
Figure 1.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
®
Remote Thermal
ADT7468
control mode
MIN
www.analog.com

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Summary of Contents for Analog Devices dBCool ADT7468

  • Page 1 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use.

  • Page 2: Table Of Contents

    ADT7468 TABLE OF CONTENTS Specifications..................3 PWM Logic State................ 34 Absolute Maximum Ratings............5 Fan Speed Control..............34 ESD Caution.................. 5 Miscellaneous Functions ............... 35 Pin Configuration and Function Descriptions......6 Operating from 3.3 V Standby ..........35 Typical Performance Characteristics ..........8 XNOR Tree Test Mode ..............

  • Page 3: Specifications

    ADT7468 SPECIFICATIONS to T to V , unless otherwise noted. All voltages are measured with respect to GND, unless otherwise specified. Typicals are at T = 25°C and represent most likely parametric norms. Logic inputs accept input high voltages up to V even when device is operating down to V .
  • Page 4 ADT7468 Parameter Unit Test Conditions/Comments OPEN-DRAIN DIGITAL OUTPUTS, PWM1 TO PWM3, XTO Current Sink, I Output Low Voltage, V = −8.0 mA, V = +3.3 V High Level Output Current, I μA OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA) Output Low Voltage, V = −4.0 mA, V = +3.3 V High Level Output Current, I...

  • Page 5: Absolute Maximum Ratings

    ADT7468 ABSOLUTE MAXIMUM RATINGS Table 2. Stresses above those listed under Absolute Maximum Ratings Parameter Rating may cause permanent damage to the device. This is a stress Positive Supply Voltage (V 5.5 V rating only; functional operation of the device at these or any Maximum Voltage on 12 V 20 V other conditions above those indicated in the operational...

  • Page 6: Pin Configuration And Function Descriptions

    ADT7468 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS PWM1/XTO +2.5V +12V /VID5 VID0 /THERM ADT7468 VID1 VID4 TOP VIEW VID2 (NOT TO SCALE) VID3 D1– TACH3 PWM2/SMBALERT D2– TACH4/GPIO/THERM/SMBALERT TACH1 TACH2 PWM3 Figure 3. Pin Configuration Table 3. Pin Function Descriptions Mnemonic Description Digital I/O (Open Drain).
  • Page 7 ADT7468 Mnemonic Description Anode Connection to First Thermal Diode. VID4 Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Analog Input. Monitors +5 V power supply. THERM Alternatively, this pin can be reconfigured as a bidirectional THERM pin. Can be used to time and monitor assertions on the THERM input.

  • Page 8: Typical Performance Characteristics

    ADT7468 TYPICAL PERFORMANCE CHARACTERISTICS 100mV –10 –20 40mV –30 –40 –50 –5 60mV –60 –10 100M CAPACITANCE (nF) FREQUENCY (kHz) Figure 4. Temperature Error vs. Capacitance between D+ and D− Figure 7. Remote Temperature Error vs. Common Mode Noise Frequency –10 20mV –20...
  • Page 9 ADT7468 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 –4.0 –40 –20 POWER SUPPLY VOLTAGE (V) TEMPERATURE (°C) Figure 13. Internal Temperature Error vs. ADT7468 Temperature Figure 10. Shutdown I vs. Power Supply INT ERROR, 250mV –0.5 –1.0 –1.5 –2.0 –5 –2.5 –10 INT ERROR, 100mV...

  • Page 10: Product Description

    ADT7468 PRODUCT DESCRIPTION On the ADT7463, the measurement range is from −127°C The ADT7468 is a complete thermal monitor and multiple fan to +127°C. This means that the ADT7468 can measure controller for any system requiring thermal monitoring and higher temperatures. The ADT7468 also includes the cooling.

  • Page 11: Recommended Implementation

    ADT7468 Bit 1 = 1 switches the fan drive to low frequency PWM, RECOMMENDED IMPLEMENTATION programmable between 10 Hz and 100 Hz, the same as the Configuring the ADT7468 as in Figure 15 allows the system ADT7463. The default = 0 = HF PWM. designer to use the following features: Bit 2 sets the direction for the GPIO: 0 = input, 1 = output.

  • Page 12: Serial Bus Interface

    ADT7468 SERIAL BUS INTERFACE following functions. To write data to one of the device data On PCs and servers, control of the ADT7468 is carried out registers or read data from it, the address pointer register must using the serial system management bus (SMBus). The be set so that the correct data register is addressed, then data ADT7468 is connected to this bus as a slave device, under the can be written into that register or read from it.

  • Page 13: Write Operations

    ADT7468 START BY ACK. BY ACK. BY STOP BY MASTER ADT7468 ADT7468 MASTER FRAME 1 FRAME 2 SERIAL BUS ADDRESS BYTE ADDRESS POINTER REGISTER BYTE Figure 17. Writing to the Address Pointer Register Only ACK. BY START BY NO ACK. BY STOP BY ADT7468 MASTER...

  • Page 14: Read Operations

    ADT7468 Write Byte In this operation, the master device sends a command byte and SLAVE DATA ADDRESS one data byte to the slave device, as follows: Figure 21. Single Byte Read from a Register The master device asserts a start condition on SDA. Alert Response Address The master sends the 7-bit slave address followed by the Alert response address (ARA) is a feature of SMBus devices that...

  • Page 15: Vid Code Monitoring

    ADT7468 VID CODE MONITORING VID Code Input Threshold Voltage The ADT7468 has five dedicated voltage ID (VID code) The switching threshold for the VID code inputs is approxi- inputs. These are digital inputs that can be read back through mately 1 V. To enable future compatibility, it is possible to the VID register (Reg.

  • Page 16: Analog-To-Digital Converter

    ADT7468 ANALOG-TO-DIGITAL CONVERTER Voltage Limit Registers All analog inputs are multiplexed into the on-chip, successive Associated with each voltage measurement channel is a high approximation, analog-to-digital converter, which has a resolu- and low limit register. Exceeding the programmed high or low tion of 10 bits.
  • Page 17 ADT7468 Single-Channel ADC Conversion TACH1 Minimum High Byte (Reg. 0x55) Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the <7:5> Selects ADC channel for single-channel convert mode. ADT7468 into single-channel ADC conversion mode. In this Table 5. Programming the Single Channel ADC Function mode, the ADT7468 can be made to read a single voltage Bits <7:5>...

  • Page 18: Temperature Measurement

    ADT7468 This is given by TEMPERATURE MEASUREMENT Δ / × A simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, measuring the base- emitter voltage (V ) of a transistor, operated at constant where: current.
  • Page 19 ADT7468 The results of remote temperature measurements are stored in Factors Affecting Diode Accuracy 10-bit, twos complement format, as illustrated in Table 7. The Remote Sensing Diode extra resolution for the temperature measurements is held in The ADT7468 is designed to work with either substrate the Extended Resolution Register 2 (Reg.
  • Page 20 ADT7468 Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23 Nulling Temperature Errors packages, are suitable devices to use. As CPUs are developed that run faster, it is getting more difficult to avoid high frequency clocks when routing the Table 7. Temperature Data Format D+/D–...

  • Page 21: Additional Adc Functions For Temperature Measurement

    ADT7468 Temperature Measurement Limit Registers Table 10. Conversion Time with Averaging Enabled Channel Measurement Time Each temperature measurement channel is associated with high Voltage Channels 11 ms and low limit registers. Exceeding the programmed high or low Remote Temperature 39 ms limit causes the appropriate status bit to be set.

  • Page 22: Limits, Status Registers, And Interrupts

    ADT7468 LIMITS, STATUS REGISTERS, AND INTERRUPTS LIMIT VALUES THERM Limit Register Each measurement channel on the ADT7468 is associated with Reg. 0x7A, THERM limit = 0x00 default high and low limits. These can form the basis of system status 16-Bit Limits monitoring;...

  • Page 23: Status Registers

    ADT7468 Since the ADC normally runs freely in this manner, the time Status Register 1 (Reg. 0x41) taken to monitor all the analog inputs is usually not of interest, Bit 7 (OOL) = 1, denotes a bit in Status Register 2 is set and because the most recently measured value of any input can be Status Register 2 should be read.
  • Page 24 ADT7468 HIGH LIMIT HIGH LIMIT TEMPERATURE TEMPERATURE CLEARED ON READ “STICKY” (TEMP BELOW LIMIT) CLEARED ON READ STATUS BIT (TEMP BELOW LIMIT) “STICKY” STATUS BIT TEMP BACK IN LIMIT TEMP BACK IN LIMIT (STATUS BIT STAYS SET) (STATUS BIT STAYS SET) SMBALERT SMBALERT INTERRUPT...
  • Page 25 ADT7468 Enabling the SMBALERT Interrupt Output The SMBALERT interrupt function is disabled by default. Pin 10 or Pin 14 can be reconfigured as an SMBALERT output to signal out-of-limit conditions. THERM Table 12. Configuring Pin 10 as SMBALERT Output Register Bit Setting Configuration Register 3 <0>...
  • Page 26 ADT7468 If the THERM timer is read during a THERM assertion, then THERM the following happens: THERM 0 0 0 0 0 0 1 The contents of the timer are cleared. TIMER 7 6 5 3 2 1 0 THERM ASSERTED (REG.
  • Page 27 ADT7468 Configuring the Relevant THERM Behavior can be calculated for a fixed THERM timer limit time. For example, if it takes one week for a THERM timer limit of Configure the desired pin as the THERM timer input. 2.914 secs to be exceeded and the next time it takes only Setting Bit 1 ( THERM timer enable) of Configuration one hour, then this is an indication of a serious degradation in system performance.

  • Page 28: Active Cooling

    ADT7468 ACTIVE COOLING Figure 34 uses a 10 kΩ pull-up resistor for the TACH signal. This assumes that the TACH signal is an open-collector from DRIVING THE FAN USING PWM CONTROL the fan. In all cases, the TACH signal from the fan must be kept The ADT7468 uses pulse-width modulation (PWM) to control below 5 V maximum to prevent damaging the ADT7468.
  • Page 29 ADT7468 Driving Two Fans from PWM3 Driving up to Three Fans from PWM3 The ADT7468 has four TACH inputs available for fan speed TACH measurements for fans are synchronized to particular measurement, but only three PWM drive outputs. If a fourth PWM channels;...

  • Page 30: Laying Out 2-Wire And 3-Wire Fans

    ADT7468 Driving 2-Wire Fans For fans that draw more current, such as larger desktop or server fans, R can be reduced for the same programmed The ADT7468 can support 2-wire fans only when the low SENSE threshold. The smaller the threshold programmed the better, frequency PWM mode is selected in Configuration Register 5, because more voltage is developed across the fan and the fan Bit 2.

  • Page 31: Fan Speed Measurement

    ADT7468 If the fan output has a resistive pull-up to 12 V (or other voltage FAN SPEED MEASUREMENT greater than 5 V) then the fan output can be clamped with a The fan counter does not count the fan TACH output pulses Zener diode, as shown in Figure 43.
  • Page 32 ADT7468 Calculating Fan Speed The fan tachometer reading registers report back the number of Assuming a fan with a two pulses per revolution (and two 11.11 μs period clocks (90 kHz oscillator) gated to the fan speed pulses per revolution being measured), fan speed is calculated counter, from the rising edge of the first fan TACH pulse to the rising edge of the third fan TACH pulse (assuming two pulses per revolution are being counted).

  • Page 33: Fan Spin-Up

    ADT7468 2-Wire Fan Speed Measurements Using Configuration Register 4 (0x40) Bit 5 (FSPDIS), this (Low Frequency Mode Only) functionality can be changed (see the Disabling Fan Start-Up Timeout section). The ADT7468 is capable of measuring the speed of 2-wire fans, that is, fans without TACH outputs.

  • Page 34: Pwm Logic State

    ADT7468 overheating. The automatic fan speed control incorporates a PWM LOGIC STATE feature called dynamic T calibration, which reduces the The PWM outputs can be programmed high for 100% duty design effort required to program the automatic fan speed cycle (noninverted) or low for 100% duty cycle (inverted). control loop.

  • Page 35: Miscellaneous Functions

    ADT7468 MISCELLANEOUS FUNCTIONS VID0 OPERATING FROM 3.3 V STANDBY VID1 The ADT7468 has been specifically designed to operate from a 3.3 V STBY supply. In computers that support S3 and S5 states, VID2 the core voltage of the processor is lowered in these states. If using the dynamic T mode, lowering the core voltage of the VID3...
  • Page 36 ADT7468 ADT7468 IS POWERED UP HAS THE ADT7468 BEEN ACCESSED BY A VALID SMBUS TRANSACTION? IS V ABOVE 0.75V? CHECK V START FAIL-SAFE TIMER HAS THE ADT7468 BEEN ACCESSED BY A VALID SMBUS TRANSACTION? FAIL-SAFE TIMER ELAPSES AFTER THE FAIL-SAFE TIMEOUT HAS THE ADT7468 BEEN RUN THE FANS TO FULL SPEED ACCESSED BY A VALID...

  • Page 37: Automatic Fan Control Overview

    ADT7468 AUTOMATIC FAN CONTROL OVERVIEW The ADT7468 can automatically control the speed of fans based Figure 49 gives a top level overview of the automatic fan control upon the measured temperature. This is done independently of circuitry on the ADT7468. From a systems-level perspective, up CPU intervention once initial parameters are set up.

  • Page 38: Dynamic Tmin Control Mode

    ADT7468 VENTS DYNAMIC T CONTROL MODE I/O CARDS In addition to the automatic fan speed control mode described VENTS POWER I/O CARDS POWER in the Automatic Fan Control Overview section, the ADT7468 SUPPLY SUPPLY has a mode that extends the basic automatic fan speed control loop.
  • Page 39 ADT7468 Dynamic T Control Overview Operating Point Registers Dynamic T control mode builds upon the basic automatic Reg. 0x33, Remote 1 operating point = 0xA4 (100°C default) fan control loop by adjusting the T value based on system Reg. 0x34, local operating point = 0xA4 (100°C default) performance and measured temperature.

  • Page 40: Programming The Automatic Fan Speed Control Loop

    ADT7468 PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP • 5 V voltage monitoring or overtemperature THERM Note that to more efficiently understand the automatic fan function? speed control loop, it is strongly recommended to use the • ADT7468 evaluation board and software while reading this 12 V voltage monitoring or VID5 input? section.
  • Page 41 ADT7468 Recommended Implementation 1 VRM temperature using local temperature sensor. Configuring the ADT7468 as shown in Figure 54 provides the CPU temperature measured using the Remote 1 system designer with the following features: temperature channel. Six VID inputs (VID0 to VID5) for VRM10 support. 10.
  • Page 42 ADT7468 Recommended Implementation 2 5 V measurement input. Configuring the ADT7468 as in Figure 55 provides the system VRM temperature using local temperature sensor. designer with the following features: CPU temperature measured using the Remote 1 Six VID inputs (VID0 to VID5) for VRM10 support. temperature channel.

  • Page 43: Step 2: Configuring The Mux

    ADT7468 101 = Fastest speed calculated by local and Remote 2 STEP 2: CONFIGURING THE MUX temperature controls PWMx After the system hardware configuration is determined, the fans can be assigned to particular temperature channels. Not only 110 = Fastest speed calculated by all three temperature can fans be assigned to individual channels, but the behavior of channels controls PWMx the fans is also configurable.
  • Page 44 ADT7468 Example Mux Settings Mux Configuration Example <7:5> (BHVR), PWM1 Configuration Register 0x5C. This is an example of how to configure the mux in a system using the ADT7468 to control three fans. The CPU fan sink is 101 = Fastest speed calculated by local and Remote 2 controlled by PWM1, the front chassis fan is controlled by temperature controls PWM1 PWM2, and the rear chassis fan is controlled by PWM3.

  • Page 45: Min

    ADT7468 Registers STEP 3: T SETTINGS FOR THERMAL CALIBRATION CHANNELS Reg. 0x67, Remote 1 temperature T = 0x9A (90°C) is the temperature at which the fans start to turn on under Reg. 0x68, Local temperature T = 0x9A (90°C) automatic fan control. The speed at which the fan runs at T programmed later.

  • Page 46: Step 4: Pwm Min For Each Pwm (Fan) Output

    ADT7468 STEP 4: PWM FOR EACH PWM (FAN) OUTPUT Programming the PWM Registers is the minimum PWM duty cycle at which each fan in The PWM registers are 8-bit registers that allow the mini- the system runs. It is also the start speed for each fan under mum PWM duty cycle for each output to be configured automatic fan control once the temperature rises above T anywhere from 0% to 100%.

  • Page 47: Step 6: Trange For Temperature Channels

    Using the ADT7468 evaluation software, you can Value = 128 (decimal) or 80 (hex) graphically program and visualize this functionality. Ask your local Analog Devices representative for details. Example 2: For a minimum PWM duty cycle of 75%, Value (decimal) = 75/0.39 = 85 (decimal)
  • Page 48 ADT7468 Example: Calculate T , given that T = 30°C, T = 40°C, RANGE 100% and PWM = 33% duty cycle = 85 (decimal). + (Max DC − Min DC) × T /170 RANGE = 30°C + (100% − 33%) × 40°C/170 = 30°C + (255 −...
  • Page 49 ADT7468 2°C Increasing or decreasing PWM changes the effective T RANGE 2.5°C although the fan control still follows the same PWM duty cycle 3.33°C to temperature slope. The effective T for different PWM 4°C RANGE 5°C values can be calculated using Equation 2: 6.67°C 8°C + (Max DC −...

  • Page 50: Step 7: Ttherm For Temperature Channels

    ADT7468 The fans remain running at 100% until the temperature drops below T minus hysteresis, where hysteresis is the number THERM programmed into the hysteresis Registers 0x6D and 0x6E. The default hysteresis value is 4°C. The T limit should be considered the maximum worst-case THERM operating temperature of the system.

  • Page 51: Step 8: Thyst For Temperature Channels

    ADT7468 RANGE 100% THERM THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE CONFIG...

  • Page 52: Step 9: Operating Points For Temperature Channels

    ADT7468 RANGE 100% THERM THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE CONFIG...

  • Page 53: Step 10: High And Low Limits For Temperature Channels

    ADT7468 THERMAL CALIBRATION 100% CONFIG OPERATING RAMP POINT CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE CONFIG LOCAL =...
  • Page 54 ADT7468 Local = CYL = Bits <5:3> of Calibration Control Register 2 WAIT 2n MONITORING (Address = 0x37). CYCLES CURRENT Remote 2 = CYR2 = Bits <7:6> of Calibration Control Register 2 TEMPERATURE MEASUREMENT and Bit 0 of Calibration Control Register 1 (Address = 0x36). T1(n) DECREASE T IS T1(n) >...
  • Page 55 ADT7468 range (OP − Hyst), because the temperature has not exceeded can increase if the operating temperature. • The measured temperature has fallen below the low Once the temperature exceeds the operating temperature, the temperature limit. This means the user must choose the long cycle causes T to be reduced by 1°C every long cycle low limit carefully.

  • Page 56: Step 11: Monitoring Therm

    ADT7468 The optimal operating point for the processor is determined by Figure 75 shows how T increases when the current tempera- monitoring the thermal monitor in the Intel Pentium 4 proces- ture is above T and below the low temperature limit, and sor.

  • Page 57: Step 12: Ramp Rate For Acoustic Enhancement

    ADT7468 R2T = 0, disables dynamic T control. The T value chosen <6:4> ACOU2, selects the ramp rate for PWM2. is not adjusted and the channel behaves as described in the 000 = 1 time slot = 35 sec Automatic Fan Control Overview section. 001 = 2 time slots = 17.6 sec <6>...
  • Page 58 ADT7468 Figure 81 shows the behavior of the PWM output as tempera- (°C) TEMP ture varies. As the temperature increases, the fan speed ramps up. Small drops in temperature do not affect the ramp-up function, because the newly calculated fan speed is still higher than the previous PWM value.
  • Page 59 ADT7468 Enhance Acoustics Register 2 (Reg. 0x63) <6:4> ACOU2, selects the ramp rate for PWM2. <2:0> ACOU3, selects the ramp rate for PWM3. 000 = 140 sec 001 = 70.4 sec 000 = 140 sec 010 = 47.2 sec 001 = 70.4 sec 011 = 28 sec 010 = 47.2 sec 100 = 17.6 sec...

  • Page 60: Enhancing System Acoustics

    ADT7468 ENHANCING SYSTEM ACOUSTICS ACOUSTIC ENHANCEMENT MODE OVERVIEW Automatic fan speed control mode reacts instantaneously to changes in temperature, that is, the PWM duty cycle responds Figure 82 gives a top-level overview of the automatic fan control immediately to temperature change. Any impulses in temp- circuitry on the ADT7468 and shows where acoustic enhance- erature can cause an impulse in fan noise.
  • Page 61 ADT7468 Approaches to System Acoustic Enhancement period, T, the PWM period is subdivided into 255 equal time slots. One time slot corresponds to the smallest possible incre- There are two different approaches to implementing system ment in the PWM duty cycle. A PWM signal of 33% duty cycle acoustic enhancement: temperature-centric and fan-centric.

  • Page 62: Register Tables

    ADT7468 REGISTER TABLES Table 17. Register Map Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x20 2.5 V 0x00 measurement 0x21 measurement 0x00 0x22 measurement 0x00 0x23 5 V measurement 0x00 0x24 12 V measurement...
  • Page 63 ADT7468 Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x4B 5 V High Limit 0xFF 0x4C 12 V Low Limit 0x00 0x4D 12 V High Limit 0xFF 0x4E Remote 1 Temp 0x01 Low Limit...
  • Page 64 ADT7468 Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x6B Local THERM 0XA4 Temp Limit 0x6C Remote 2 THERM 0XA4 Temp Limit 0x6D Remote 1 and HYSR1 HYSR1 HYSR1 HYSR1 HYSL...
  • Page 65 ADT7468 1, 2, 3 Table 19. Temperature Reading Registers (Power-On Default = 0x01) Register Address Description Read only 3, 4 0x25 Remote 1 temperature reading (8 MSBs of reading). 0x26 Read only Local temperature reading (8 MSBs of reading). 3, 4 0x27 Read only Remote 2 temperature reading...
  • Page 66 ADT7468 Table 23. Register 0x36—Dynamic T Control Register 1 (Power-On Default = 0x00) Name Description <0> CYR2 Read/write MSB of 3-bit remote 2 cycle value. The other two bits of the code reside in Dynamic T Control Register 2 (Reg. 0x37). These three bits define the delay time between making subsequent T adjustments in the control loop, in terms of the number of monitoring cycles.
  • Page 67 ADT7468 Table 24. Register 0x37—Dynamic T Control Register 2 (Power-On Default = 0x00) Name Description <2:0> CYR1 Read/write 3-Bit Remote 1 Cycle Value. These three bits define the delay time between making subsequent T adjustments in the control loop for the Remote 1 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop.
  • Page 68 ADT7468 Table 26. Register 0x40—Configuration Register 1 (Power-On Default = 0x01) Name Description <0> STRT Read/write Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed. Logic 0 disables monitoring and PWM control based on the default power-up limit settings. Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and the default settings are enabled.
  • Page 69 ADT7468 Table 28. Register 0x42—Interrupt Status Register 2 (Power-On Default = 0x00) Name Description <0> 12V/VC Read only A one indicates that the 12 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided.
  • Page 70 ADT7468 Table 31. Temperature Limit Registers Register Address Description Power-On Default 0x4E Read/write Remote 1 temperature low limit 0x81 0x4F Read/write Remote 1 temperature high limit 0x7F 0x50 Read/write Local temperature low limit 0x81 0x51 Read/write Local temperature high limit 0x7F 0x52 Read/write...
  • Page 71 ADT7468 Table 34. PWM Configuration Registers Register Address Description Power-On Default 0x5C Read/write PWM1 configuration. 0x82 0x5D Read/write PWM2 configuration. 0x82 0x5E Read/write PWM3 configuration. 0x82 Name Description <2:0> SPIN Read/write These bits control the startup timeout for PWMx. The PWM output stays high until two valid TACH rising edges are seen from the fan.
  • Page 72 ADT7468 Table 35. TEMP T /PWM Frequency Registers RANGE Register Address Description Power-On Default 0x5F Read/write Remote 1 T /PWM1 frequency. 0xC4 RANGE 0x60 Read/write Local temperature T /PWM2 frequency. 0xC4 RANGE 0x61 Read/write Remote 2 T /PWM3 frequency. 0xC4 RANGE Name Description...
  • Page 73 ADT7468 Table 36. Register 0x62—Enhanced Acoustics Register 1 (Power-On Default = 0x00) Name Description <2:0> ACOU Read/write These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 ramps gracefully at the rate determined by these bits. This feature enhances the acoustics of the fan being driven by the PWM1 output.
  • Page 74 ADT7468 Table 37. Register 0x63 – Enhanced Acoustics Register 2 (Power-On Default = 0x00) Name Description <2:0> ACOU3 Read/write These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping instantaneously to its newly calculated speed, PWM3 ramps gracefully at the rate determined by these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output.
  • Page 75 ADT7468 Table 40. THERM Limit Registers Register Address Description Power-On Default Remote 1 THERM limit. 0x6A Read/write 0x64 (100°C) Local THERM limit. 0x6B Read/write 0x64 (100°C) Remote 2 THERM limit. 0x6C Read/write 0x64 (100°C) If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism incorporated to cool the system in the event of a critical overtemperature.
  • Page 76 ADT7468 Table 44. Local Temperature Offset Register Address Description Power-On Default 0x71 Read/write Local temperature offset. 0x00 <7:0> Read/write Allows a twos complement offset value to be automatically added to or subtracted from the local temperature reading. LSB value = 0.5°C. This register becomes read-only when the Configuration Register 1 lock bit is set to 1.
  • Page 77 ADT7468 Table 47. Register 0x74—Interrupt Mask Register 1 (Power-On Default <7:0> = 0x00) Name Description 2.5V Read/write 2.5 V = 1, masks SMBALERT for out-of-limit conditions on the 2.5 V channel. Read/write = 1, masks SMBALERT for out-of-limit conditions on the V channel.
  • Page 78 ADT7468 Table 51. Register 0x78—Configuration Register 3 (Power-On Default = 0x00) Name Description <0> ALERT Read/write ALERT = 1, Pin 10 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-of-limit error conditions. ALERT = 0, Pin 10 (PWM2/SMBALERT) is configured as the PWM2 output. <1>...
  • Page 79 ADT7468 Table 54. Register 0x7B—TACH Pulses per Revolution Register (Power-On Default = 0x55) Name Description <1:0> FAN1 Read/write Sets number of pulses to be counted when measuring Fan 1 speed. Can be used to determine fan pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (default)
  • Page 80 ADT7468 Table 56. Register 0x7D—Configuration Register 4 (Power-On Default = 0x00) Name Description <1:0> PIN14FUNC Read/write These bits set the functionality of Pin 14: 00 = TACH4 (default) 01 = Bidirectional THERM 10 = SMBALERT 11 = GPIO <3:2> AINL Read/write These two bits define the input threshold for 2-wire fan speed measurements (low frequency mode only):...

  • Page 81: Adt7468 Programming Block Diagram

    ADT7468 PROGRAMMING BLOCK DIAGRAM Figure 85.

  • Page 82: Outline Dimensions

    ADT7468 OUTLINE DIMENSIONS 0.341 0.154 0.236 PIN 1 0.065 0.069 0.049 0.053 8° 0.010 0.025 0° 0.012 SEATING 0.050 0.004 0.010 0.008 PLANE 0.016 0.006 COPLANARITY 0.004 COMPLIANT TO JEDEC STANDARDS MO-137AE Figure 86. 24-Lead Shrink Small Outline Package [QSOP] (RQ-24) Dimensions shown in inches ORDERING GUIDE...
  • Page 83 ADT7468 NOTES...
  • Page 84 ADT7468 NOTES © 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04499–0–7/05(A)

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