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Analog Devices dBCool ADT7473 Manual

Analog Devices dBCool ADT7473 Manual

Remote thermal monitor and fan controller
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FEATURES
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 optimizes system acoustics
MIN
intelligently
Automatic fan speed control mode controls 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®4 processor
Thermal control circuit via THERM input
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)
Fully ROHS compliant
PWM1
PWM2
PWM3
TACH1
TACH2
TACH3
TACH4
THERM
V
CC
D1+
D1–
D2+
D2–
V
CCP
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 registered trademarks are the property of their respective owners.

FUNCTIONAL BLOCK DIAGRAM

ADT7473
PWM
REGISTERS
ACOUSTIC
AND
ENHANCEM NT
E
CONTROLLERS
CONTROL
(HF AND LF)
FAN
SPEED
COUNTER
PERFORMANC
MONITORING
THERMAL
PROTECTION
V
TO ADT7473
CC
INPUT
SIGNAL
SRC
CONDITION G
IN
AND
ANALOG
MULTIPLEXER
BAND GAP
TEMP SENSOR
Cool
Monitor and Fan Controller
GENERAL DESCRIPTION
The ADT7473 dBCool controller is a thermal monitor and
multiple PWM fan controller for noise sensitive or power
sensitive applications requiring active system cooling. The
ADT7473 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 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 ADT7473 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
AU
TOMATIC
FAN SPEED
C
ONTROL
D
YNAMIC
T
MIN
C
ONTROL
E
10-BIT
ADC
BAND GAP
R
EFERENCE
GND
Figure 1.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
®
Remote Thermal
ADT7473
control mode
MIN
ADDRESS
POINTER
REGISTER
PWM
CONFIGURATION
REGISTERS
INTERRUPT
MASKING
INTERRUPT
STATUS
REGISTERS
LIMIT
COMPARATORS
VALUE AND
LIMIT
REGISTERS
www.analog.com
©2006 Analog Devices, Inc. All rights reserved.

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  • Page 1: Fe Atures

    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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

  • Page 2: Table Of Contents

    ADT7473 ABLE OF CONTENTS atures ....................1 mits, Status Registers, and Interrupts........20 eneral Description ................. 1 Limit Values ................20 Functional Block Diagram .............. 1 Interrupt Status Registers ............21 ecifications..................4 THERM Timer ................23 Timing Diagram ................5 Fan Presence Detect..............
  • Page 3 ADT7473 REVISION HISTORY Changes to Interrupt Mask Register 1 (0x74) Section ....22 2/06—Rev. 0 to Rev. A. Changes to Fan Drive Using PWM Control........26 Changes t o Table 1 ................4 Changes to Reading Fan Speed from the ADT7473....28 Change to T able 3 ................6 hange s to O...

  • Page 4: Specifications

    ADT7473 SPECIFICATIONS to T to V , unless other wise noted. Table 1. rameter est Conditions/Comments POWER SUPPLY Supply Voltage Supply Current, I terface inactive, ADC active MP-TO-DIGITAL CONV ERTER Local Sensor Accuracy ± ±1.5 °C 0°C ≤ ≤ 85°C ±2.5 °C −40°C...

  • Page 5: Timing Diagram

    ADT7473 Parameter Unit Test Conditions/Comments DIGITAL INPUT LOGIC LEVELS (TACH INPUTS) Input High Voltage, V Maximum input voltage Input Low Voltage, V −0.3 Minimum input voltage Hysteresis V p-p DIGITAL INPUT LOGIC LEVELS (THERM) ADTL+ Input High Voltage, V 0.75 × V Input Low Voltage, V D IGITAL INPUT CURRENT Input High Current, I...

  • Page 6: Absolute Maximum Ratings

    ADT7473 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 3.6 V rating only; functional operation of the device at these or any Voltage on Any Input or Output Pin −0.3 V to +3.6 V other conditions above those indicated in the operational...

  • Page 7: Pi N Configuration And Function Descriptions

    ADT7473 PIN CONFIGURATION AND FUNCTION DESCRI PTIONS PWM1/XTO ADT7473 TACH3 TOP VIEW PWM2/SMBALERT D1– (Not to Scale) TACH1 TACH2 D2– PWM3 TACH4/GPIO/THERM/SMBALERT Figure 3. Pin Configuration Table 4. Pin Function Descriptions Pin No. Mnemonic Description Digital Input (Open Drain). SMBus serial clock input. Requires SMBus pull-up. Ground Pin for the ADT7473.

  • Page 8: Typical Performance Characteristics

    ADT7473 TYPICAL PERFORMANCE CHARACTERISTICS D+ TO GND 100mV D+ TO V 60mV –20 40mV –40 –60 –10 100M 200M 300M 400M 500M 600M LEAKAGE RESISTANCE (MΩ) NOISE FREQUENCY (Hz) Figure 4. Remote Tempera re Error vs. PCB Resistance Figure 7. Remote Temperature Error s. Common-Mode Noise Frequency 1.20 1.18 –10...
  • Page 9 ADT7473 250mV –2 100mV –4 –6 –0.5 –8 –1.0 –10 –1.5 –12 –2.0 100M 200M 300M 400M 500M 600M –40 –20 FREQUENCY (Hz) OIL BA TH TEMPERATURE (°C) Figure 10. Remote Temperature Error vs. Power Supply Noise Frequency Figure 12. Remote Temperature Error vs. Tempe rature –0.5 –1.0...

  • Page 10: Product Description

    ADT7473 PRODUCT DESCRIPT HOW TO SET THE FUNCTIONALITY OF PIN 9 The ADT7473 is a complete thermal monitor and multiple fan controller for any system requiring thermal monitoring and Pin 9 on the ADT7473 has four possible functions: SMBA LERT cooling.

  • Page 11: Serial Bus Interface

    ADT7473 SERIAL BUS INTERFACE In t e ADT7473, write operations c ontain either one or two byt , and read operations contain on e byte. To write data to On PCs and servers, control of the ADT7473 is carri ed out using the SMBus.

  • Page 12: Write Operations

    ADT7473 ACK. BY START BY ACK. BY STOP BY ADT7473 MASTER ADT7473 MASTER FRAME 1 FRAME 2 SERIAL BUS ADDRESS BYTE ADDRESS POINTER REGISTER BYTE Figure 15. Writing to the Address Pointer Register Only START BY ACK. BY NO ACK. BY STOP B ADT7473 MASTER...

  • Page 13: Read Operations

    ADT7473 Once the ADT7473 has responded to t he alert response address, READ OPERATIONS the master must read the status registers, and the SMBALERT is The ADT7473 uses the following SMBus read protocols. cleared only if the error condition is gone. Receive Byte SMBus TIMEOUT This operation is useful when repeatedly r...

  • Page 14: Vccp Limit Registers

    ADT7473 Bypass Voltage Input Attenuator LIMIT REGISTERS ting Bit 5 of Configuration Register 2 (0x73) removes the ssoci ated wi th the V measureme t channel is a high and attenuati on circuitry from the input. This al lows the user low limit regi ster.

  • Page 15: Temperature Measurement Method

    ADT7473 Table 7. 10-Bit ADC Output Codes vs ADC Outp (3.3 V Decimal Binary (10 Bits) <0.0042 <0.00293 00000000 00 0.0042 to 0.0085 0.0293 to 0.0058 00000000 01 0.0085 to 0.0128 0.0058 to 0.0087 00000000 10 0.0128 to 0.0171 0.0087 to 0.0117 00000000 11 0.0171 to 0.0214 0.0117 to 0.0146...
  • Page 16 ADT7473 Local Temperature Measurement Remote Temperature Measurement The ADT7473 contains an on-chip band gap temperature The ADT7473 can measure the temperature of two remote sensor whose output is digitized by the on-chip 10-bit ADC. diode sensors or diode-connected transistors connected to The 8-bit MSB temperature data is stored in the local tempera- Pin 10 and Pin 11, or Pin 12 and Pin 13.

  • Page 17: Series Resistance Cancellation

    ADT7473 The construction of a filter allows t he ADT7473 and the remote ADT7473 temperature sensor to operate in noisy environments. Figure 24 2N3904 shows a low-pass R-C filter with the following values: D– R = 100 Ω, C = 1 nF This filtering reduces both common-mod e noise and Figure 22.
  • Page 18 ADT7473 To factor this i n, the user can w rite the ∆T value to the ADT7460/ADT7473 Backw ards-Compatible Mode offset register. Then, the ADT7473 automatically a dds it to By setting Bit 1 of Configuration Register 5 (0x7C), all tempera- or su btracts it from the tempe rature measurement.

  • Page 19: Additional Adc Functions For Temperature Measurement

    ADT7473 ADDITIONAL ADC FUNCTIONS FOR Overtemperature Events TEMPERATURE MEASUREMENT Overtemperature even ts on any of the temperature channels can A number of other functions are available on the ADT7473 to be detected and dealt with automatically in automatic fan sp offer the system designer increased flexibility.

  • Page 20: Li Mits, Status Registers, And Interrupts

    ADT7473 LIMITS, STATUS REGISTERS, AND INTERR UPTS Fan Limit Registers LIMIT VALUES Register 0x54, TACH1 Minimum Low Byte = 0xFF default Associated with each measurement channel on the ADT74 are high and low limits. These can form the basis of system Register 0x55, TACH1 Minimum High Byte = 0xFF def ault status monitoring;...

  • Page 21: Interrupt Status Registers

    ADT7473 As mentioned previously, the ADC perf orms round-robin Interrupt Status Register 2 (0x42) conversions. The total monitoring cycle time for averaged voltage Bit 7 (D2) = 1, indicates an open or short on D2+/D2– inputs. and temperature monitoring is 146 ms. The total monitoring cycle Bit 6 (D1) = 1, indicates an open or short on D1+/D1–...
  • Page 22 ADT7473 Bit 5 (LT) = 1, masks SMBALERT for local temperature. Handling SMBALERT Interrupts To prevent the system from being tied up servicing interrupts, it Bit 4 (R1T) = 1, masks SMBALERT for Remote 1 temperature. is recommended to handle the SMBALERT interrupt as follows: Bit 2 (V ) = 1, masks SMBALERT for V channel.

  • Page 23: Therm Timer

    ADT7473 The user can also set up the ADT7473 so that, when the Wh n using the THERM timer, be aware of the following. THERM pin is driven low externally, the fans run at 100%. The After a THERM timer read (0x79): fans run at 100% for the duration of the time the THERM pin is pulled low.
  • Page 24 ADT7473 Select the desired fan behavior for THERM timer events. If the THERM timer value exceeds the THERM timer limit value, the F4P bit (Bit 5) of Interrupt Status Register 2 is set and Assuming the fans are running, setting Bit 2 (BOOST) of an SMBALERT is generated.
  • Page 25 ADT7473 2.914s 2.914s 1.457s 1.457s 728.32ms 728.32ms THERM 364.16ms 364.16ms THERM TIMER TIMER LIMIT (REGISTER 0x79) 182.08ms 182.08ms (REGISTER 0x7A) 91.04ms 91.04ms 45.52ms 45.52ms 22.76ms 22.76ms 7 6 5 4 3 2 1 0 THERM THERM TIMER CLEARED ON READ MPARATOR F4P BIT (BIT 5) INTERRUPT STATUS...
  • Page 26 ADT7473 totem pole TACH output, use one of the input signal condition FAN DRIVE USING PWM CONTROL ing circuits shown in the Fan Speed Measurement section. The ADT7473 uses pulse-width modulation (PWM) to control Figure 33 shows a fan drive circuit using an NPN transistor fan speed.
  • Page 27 ADT7473 first. Care should be taken in designing drive circuits with maximum input signal range is 0 V to 3.6 V. In th e event that transistors and FETs to ensure the PWM pins are not require these inputs are supplied from fan outputs that exce ed 0 V to to source current and that they sink less than the 8 mA 3.6 V, either resistive attenuation of the fan signal...
  • Page 28 ADT7473 The fan inputs have an input resistance of nominally 160 k Ω Register 0x28, TACH1 Low Byte = 0x00 de fault ground, which should be taken into account when calculati resistor values. Register 0x29, TACH1 High Byte = 0x00 default With a pull-up voltage of 12 V and pull-up resistor less than Register 0x2A, TACH2 Low Byte = 0x00 default 1 kΩ, suitable values for R1 and R2 are 120 kΩ...
  • Page 29 ADT7473 Register 0x57, TACH2 Minimum H igh Byte = 0xFF default TACH Pulses per Rev olution Register Bits [1:0] Fan 1 default = 2 pulses per revolution Register 0x58, TACH3 Minimum Low Byte = 0xFF default Bits [3:2] Fan 2 default = 2 pulses per revolution Register 0x59, TACH3 Minimum High Byte = 0xFF default Bits [5:4] Fan 3 default = 2 pulses per revolution Register 0x5A, TACH4 Minimum Low Byte = 0xFF default...
  • Page 30 ADT7473 Disabling Fan Startup Timeout Fan Speed Control Although fan start-up makes fan spin-ups much quieter than The ADT7473 contro ls fan speed using automatic and manual fixed-time spin-ups, the option exists to use fixed spin-up modes. times. Setting Bit 5 (FSPDIS) to 1 in Configuration Register In automatic fan speed control mode, fan speed is automatically (0x40) disables the spin-up for two TACH pulses.

  • Page 31: Fan Presence Detect

    ADT7473 By reading the PWMx current duty cycle registers, the user ca Dynamic T Control Register 1 (0X36) keep track of the current duty cycle on each PWM output, even Bit [1] VCCPLO = 1 when the fans are running in automatic fan speed control mode When the V voltage drops below the V low limit, the...
  • Page 32 ADT7473 If V goes high (the system processor power rail is powered ADT7473 IS POWERED UP up), a fail-safe timer begins to count down. If the ADT7473 is not addressed by any valid SMBus transactions before the fail- HAS THE ADT7473 BEEN safe timeout (4.6 seconds) lapses, the ADT7473 drives the fans ACCESSED BY A VALID SMBus TRANSACTION?

  • Page 33: Pr Ogramming The Automatic Fan Speed Control Loop

    ADT7473 PROGRAMMING THE AUTOMATIC FAN SPEED CO T N ROL LOOP To understand the automatic fan speed control loop, it is Auto matic fan speed control reduces acoustic noise by optimiz- strongly recommended to use the ADT7473 evaluation board ing an speed according to accurately measured temperature. and software while reading this section.

  • Page 34: Step 1: Hardware Configuration

    ADT7473 STEP 1: HARDWARE CONFIGUR ATION How many fans will be supported in the system, three or four? This influences the choice of whether to us e the During system design, the motherboard sensing and control TACH4 pin or to reconfigure it for the THERM function. capabilities should be addressed early in the design stages.
  • Page 35 ADT7473 Recommended Implementation 1 • Configuring the ADT7473, as in Figure 46, provides the system CPU temperature measured using the Remote 1 designer with the following features: temperature channel. • • Two PWM outputs for fan control of up to three fans. ( Ambient temperature measured through t he Remote 2 front and rear chassis fans are connected in parallel.

  • Page 36: Step 2: Configuring The Mux

    ADT7473 STEP 2: CONFIGURING TH E MUX Automatic Fan Control Mux Options Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, Register 0 x5E. After the system hardware configuration is determined, the f can be assigned to particular temperature channels. Not only 000 = Remote 1 temperature controls PWMx can fans be assigned to individual channels, but the behavio r of...
  • Page 37 ADT7473 Example Mux Settings Mux Configuration Example Bits [7:5] (BHVR), PWM1 Configuration Register (0x5C) This is an example of how to conf igure the mux in a system using the ADT7473 to control three fans. The CPU fan sink is 101 = Fastest speed calculated by local and Remote controlled by PWM1, the front chassis fan is controlled by temperature controls PWM1...

  • Page 38: Step 3: Tmin Settings For Thermal Calibration Channels

    ADT7473 Registers STEP 3: T SETTINGS FOR THERMAL CALIBRATION CHANNELS Register 0x67, Remote 1 Temperature T = 0x9A (90°C is the temperature at which the fans start to turn on und Register 0x68, Local Temperature T = 0x9A (90°C) automatic fan control. The speed at which the fan runs at T Register 0x69, Remote 2 Temperature = 0x9A (90°C) programmed later.
  • Page 39 ADT7473 100% THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTRO PWM2 (ACOU STIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE CONFIG LOCAL = THERMAL CALIBRATION...

  • Page 40: Step 4: Pwm Min For Each Pwm (Fan) Output

    ADT7473 STEP 4: PWM FOR EACH PWM (FAN) OUTPUT Programming the PWM Registers The PWM registers are 8-bit registers that allow the is the minimum PWM duty cycle at which each fan duty cycle for each output t o be config ured the system runs.

  • Page 41: Step 6: Trange For Temperature Channels

    ADT7473 STEP 6: T FOR TEMPERATURE CHANNELS RANGE 100% is the range of temperature over which automatic fan RANGE control occurs once the programmed T temperature is exceeded. T is a temperature slope, not an arbitrary value, RANGE that is, a T of 40°C holds true only for PWM = 33%.
  • Page 42 ADT7473 is implemented a s a slope, which means that as PWM Example 3: Calculate T , given that T = 30°C, T RANGE RANGE is changed, T changes, but the actual slope remains the 40°C, and PWM = 33% duty cycle = 85 (decimal). RANGE same.
  • Page 43 ADT7473 Increasing or decreasing PWM changes the effective T The graphs in Figure 56 assume the fan starts from 0% PWM RANGE although the fan control still follows the same PWM duty cycle duty cycle. Clearly, the minimum PWM duty cycle, PWM to temperature slope.

  • Page 44: Therm

    ADT7473 Note on 4-Wire Fans The fans remain running at 100% until the temperature drops below T − hysteresis, where hysteresis is the number The control range for 4-wire fans is much wider than that of THERM -wire fans. In many cases, 4-wire fans can start with a PWM programmed into the hysteresis registers (Register 0x6D and drive of as little as 20%.

  • Page 45: Step 8: Thyst For Temperature Channels

    ADT7473 RANGE 100% THERM THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU F AN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE...
  • Page 46 ADT7473 RANGE 100% THERM THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER RANGE TACH1 EASUREMEN CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER TACH2 MEASUREMEN RANGE CONFIG LOCAL = THERMAL CALIBRATION...

  • Page 47: Dynamic Tmin Control Mode

    ADT7473 VENTS DYNAMIC T CONTROL MODE I/O CARDS In addition to th e automatic fan speed control mode described VENTS POWER I/O CARDS POWER SUPPLY in the Automatic Fan Control Overview section, the ADT7473 SUPPLY has a mode that extends the basic automatic fan speed contr loop.
  • Page 48 ADT7473 Dynamic T Control Overview Figure 63 shows an overview of the parameters that affect the operation of the dynamic T control loop. Dynamic T control mode builds up on the basic automatic fan control loop by adjusting the T value based on system performance and measured temperature.

  • Page 49: Step 9: Operating Points For Temperature Channels

    ADT7473 STEP 9: OPERATING POINTS FOR TEMPERAT Programming Operating Point Registers CHANNELS There are three operating point registers, one for each temperature channel. These 8-bit registers allow the operating The operating point for each temperature channel is the optimal point temperatures to be programmed with 1°C resolution. temperature for that thermal zone.

  • Page 50: Step 10: High And Low Limits For Temperature Channels

    ADT7473 STEP 10: HIGH AND LOW LIMITS FOR Short Cycle and Long Cycle TEMPERATURE CHANNELS The ADT7473 implements t wo loops: a short cycle and a long cycle. The short cycle takes place every n monitoring cycles. he low limit defines the temperature at which the T value The long cycle takes place every 2n monitoring cycles.
  • Page 51 ADT7473 Figure 66 shows the steps taken during the l ong cycle. Once the temperature exceeds the operating t emperature minus the hysteresis (OP − Hyst), T starts to decrease. This occur WAIT 2n MONITORING during the short cycle (see Figure 65). The rate at which T CYCLES decreases depends on the programmed value of n.

  • Page 52: Step 11: Monitoring Therm

    ADT7473 THERM LIMIT HIGH TEMP LIMIT OPERATING POINT HYSTERESIS ACTUAL NO CHANGE IN T HERE TEMP DUE TO ANY CYCLE BECAUSE T1(n) – T1 (n – 1) ≤ 0.25°C AND T1(n) < OP = > T STAYS THE SAME LOW TEMP LIMIT DECREASE HERE DUE TO DECREASE HERE DUE TO...

  • Page 53: Enhancing System Acoustics

    ADT7473 Enabling the THERM Trip Point as the Oper ating Point Dynamic Control Register 1 (0x36) TMIN Bits [4:2] of Dynamic Control Register 1 (0x36) Bit [7] R2T = 1, enables dynamic T control on the Remote 2 enable/disable THERM monitoring to program the operating temperature channel.
  • Page 54 ADT7473 ACOUSTIC ENHANCEMENT THERMAL CALIBRATION 100% CONFIG RAMP ONTROL 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 55: Step 12: Ramp Rate For Acoustic Enhancement

    ADT7473 STEP 12: RAMP RATE FOR ACOUSTIC PWM_OUT 33% DUTY ENHANCEMENT CYCLE TIME SLOTS TIME SLOTS optimal ramp rate for acoustic enhancement can be found PWM OUTPUT thro ugh system char acterization after the thermal optimization (ONE PERIOD) = 255 TIME SLOTS been finished.
  • Page 56 ADT7473 Figure 74 shows remote temper ature plotted against PWM duty Figure 76 shows the PWM output response for a ramp rate of 2. ycle for enhanced acoustics m ode. The ramp rate is set to 48, In this instance, the fan took about 17.6 seconds to reach full running speed.
  • Page 57 ADT7473 The followin g sect ions list th e ra mp-u p times when th e SLOW Figure 78 shows the behavior of the PWM output as tempera- bit is set for each PWM output. ture v aries . As th temperature in cre es, the fan speed mps up.

  • Page 58: Register Tables

    ADT7473 REGISTER TABLES Table 17. A DT 73 Registers Addre Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Defau Lock able? 0x21 Readin 0x00 0x22 Reading 0x00 0x25 Remote 1 0x01 Temperatu 0x26 Local...
  • Page 59 ADT7473 Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable? 0x50 Local Tem p Low 0x01 Limit 0x51 Local Tem p High 0xFF Limit 0x52 Remote 2 Temp 0x01 Low Limit 0x53 Remote 2 Temp...
  • Page 60 ADT7473 Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable? 0x6C Re ote 2 THERM 0xA4 p Limit 0x6D ote 1 and HYSR1 HYSR1 HYSR1 HYSR1 HYSL HYSL HYSL HYSL 0x44 Loca...
  • Page 61 ADT7473 1, 2 Table 19. Temperature Reading Registers (Power-On Default = 0x01) er Addr ss Description 3, 4 0x25 Read only Remote 1 temperature reading (8 MSB of reading). 0x26 Read only Local temperature reading (8 MSB of reading). 0x27 Read only Remote 2 temperature reading (8 MSB of reading).
  • Page 62 ADT7473 Table 23. Register 0x36—Dynamic T Control Register 1 (Power-On Default = 0x00) Descrip tion MSB of 3-bit remote 2 cycle value. The other two bits of the code reside in Dynamic T Control Register 2 (Reg. 0x 37). These three bits define the delay time between making subsequent T adjustments in t he control loop, in terms...
  • Page 63 ADT7473 Table 24. Register 0x37—Dynamic Control Register 2 (Power-On Default = 0x00) Name Description [2:0] CYR1 3-bit remote 1 cycle value. The se three bits de fine the delay time between making s ubsequen adjustments in the cont rol loo p for the Remot e 1 channel, in te rms of number of monitoring cycles...
  • Page 64 ADT7473 Table 26. Register 0x40—Configuration Register 1 (Power-On Default = 0x01) Name Description STRT Logic 1 enables m onitoring and PWM control outputs based on the limit settings programmed. Logic 0 disables m onitoring and PWM control based on the default power-up limit settings. This bit is not loc ked when Bit 1 (LOCK bit) has been written.
  • Page 65 ADT7473 Table 29. Voltage Limit Registers ister Address Description Power-On Default 0x46 low limit. 0x00 0x47 high limit. 0xFF 0x48 low limit. 0x00 0x49 high limit. 0xFF Setting the Configuration Regist er 1 lock bit has no effect on th ese registers.
  • Page 66 ADT7473 Table 34. Register 0x5C, Register 0x5D, and Register 0x5E—Configuration Register s (Power-On Default = 0x82) N me Description [2:0] These bits control the start-up timeout for PWMx. The PWM output stays high until two valid TACH rising edges are seen from the fan. If there is not a valid TACH signal during the fan TACH measurement directly after the fan start-up timeout period, then the TACH sure...
  • Page 67 ADT7473 Table 36. Register 0x5F, Register 0x60, and Register 0x61—TEMP T /PWM Freq uency Registers (Power-On Default = 0xCC) RANGE Name Description [2:0] FREQ These bits control the PWMx frequency. 000 = 11.0 Hz. 001 = 14.7 Hz. 010 = 22.1 Hz. 011 = 29.4 Hz.
  • Page 68 ADT7473 able 37. Register 0x62—Enhance Acoustics Register 1 (Power-On Default = 0x00) Name Descr iption [2:0] ACOU These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 ramps gradually at the rate determined by these bits. This feature enhances the acoustics of the fan being driven by the PWM1 output.
  • Page 69 ADT7473 Table 38. Register 0x63—Enhance Acoustics Register 2 (Power-On Default = 0x00) Name Description [2:0] ACOU3 These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping instantly to its newly calculated speed, PWM3 ramps gradually at the rate determined by these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output.
  • Page 70 ADT7473 Table 42. THERM Limit Registers Register Address Description Power-On Default 0x6A Remote 1 THERM limit. 0xA4 (100°C) 0x6B 0xA4 (100°C) Local THERM limit. 0x6C Remote 2 THERM limit. 0xA4 (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 over temperature.
  • Page 71 ADT7473 Table 47. Remote 2 Temperature Offset Register (0x72) Description Power-On Default [7:0] Allows a twos complement offset value to be automatically added to or 0x00 subtracted from the Remote 2 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.5°C. This register becomes read only when the Configuration Register 1 lock bit is set to 1.
  • Page 72 ADT7473 Table 50. Register 0x75—Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00) Name Description Read only OVT = 1, masks SMBALERT for overtemperature THERM conditions. FAN1 FAN1 = 1, masks SMBALERT for a Fan 1 fault. FAN2 FAN2 = 1, masks SMBALERT for a Fan 2 fault. FAN3 FAN3 = 1, masks SMBALERT for a Fan 3 fault.
  • Page 73 ADT7473 Table 54. Register 0x79— THERM Timer Status Register (Power-On Default = 0x00) Name Description [7:1] Read-only Times the duration THERM input is asserted. These seven bits read 0 until the THERM assertion time exceeds 45.52 ms. ASRT/ Read-only This bit is set high on the assertion of the THERM input, and is cleared on read. If the THERM assertion time TMR0 exceeds 45.52 ms, this bit is set and becomes the LSB of the 8-bit TMR reading.
  • Page 74 ADT7473 Table 57. Register 0x7C—Configuration Register 5 (Power-On Default = 0x00) Name Description TWOS Twos complement = 1, sets the temperature range to twos complement temperature range. COMPL Twos complement = 0, changes the temperature range to Offset 64. When this bit is changed, the ADT7473 interprets all relevant temperature register values as defined by this bit.
  • Page 75 ADT7473 Table 59. Register 0x7E—Manufacturer’s Test Register 1 (Power-On Default = 0x00) Name Description [7:0] Reserved Read-only Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and should not be written to under normal operation. Table 60. Register 0x7F—Manufacturer’s Test Register 2 (Power-On Default = 0x00) Name Description [7:0]...

  • Page 76: Outline Dimensions

    16-Lead QSOP RQ-16 EVAL-ADT7473EB Evaluation Board Z = Pb-free part. © 2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04686-0-2/06(A) T T T Rev. A | Page 76 of 76...

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