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ADT7476A Schematic ( PDF Datasheet ) - ON Semiconductor

Teilenummer ADT7476A
Beschreibung Remote Thermal Controller and Voltage Monitor
Hersteller ON Semiconductor
Logo ON Semiconductor Logo 




Gesamt 30 Seiten
ADT7476A Datasheet, Funktion
ADT7476A
Remote Thermal Controller
and Voltage Monitor
The ADT7476A controller is a thermal monitor and multiple PWM
fan controller for noise-sensitive or power-sensitive applications
requiring active system cooling. The ADT7476A can drive a fan using
either a low or high frequency drive signal and can monitor the
temperature of up to two remote sensor diodes plus its own internal
temperature. The part also measures and controls the speed of up to
four fans, so the fans operate at the lowest possible speed for minimum
acoustic noise.
The automatic fan speed control loop optimizes fan speed
for a given temperature. The effectiveness of the system’s thermal
solution can be monitored using the THERM input. The ADT7476A
also provides critical thermal protection to the system using the
bidirectional THERM pin as an output to prevent system or
component overheating.
Features
Monitors Up to Five Voltages
Improved TACH and PWM Performance
Controls and Monitors Up to Four Fans
High and Low Frequency Fan Drive Signal
One On-Chip and Two Remote Temperature Sensors
Extended Temperature Measurement Range Up to 191°C
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
5.0 V Support on all TACH and PWM Channels
Meets SMBus 2.0 Electrical Specifications
This Device is Pb-Free, Halogen Free and is RoHS Compliant
www.onsemi.com
QSOP−24 NB
CASE 492B
PIN ASSIGNMENT
SDA 1
24 PWM1/XTO
SCL 2
GND 3
VCC 4
VID0/GPIO0 5
VID1/GPIO1 6
VID2/GPIO2 7
VID3/GPIO3 8
ADT7476A
(Top View)
23 VCCP
22 +2.5VIN/THERM
21 +12VIN/VID5
20 +5VIN
19 VID4/GPIO4
18 D1+
17 D1−
TACH3
PWM2/
SMBALERT
TACH1
9
10
11
16 D2+
15 D2−
14 *
TACH2 12
13 PWM3/ADDREN
*TACH4/THERM/SMBALERT/GPIO6/ADDR SELECT
MARKING DIAGRAMS
ADT7476AARQZ
#YYWW
xxxx
ADT7476AARQZ = Specific Device Code
# = Pb-Free Package
YYWW
= Date Code
xxxx
= Assembly Lot Code
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 68 of this data sheet.
© Semiconductor Components Industries, LLC, 2016
February, 2016 − Rev. 7
1
Publication Order Number:
ADT7476A/D






ADT7476A Datasheet, Funktion
ADT7476A
TYPICAL PERFORMANCE CHARACTERISTICS
0
−10
−20
−30
−40
−50
−60
0 2 4 6 8 10 12 14 16 18 20 22
CAPACITANCE (nF)
Figure 3. Temperature Error vs. Capacitance
Between D+ and D−
30
25
100 mV
20
15 60 mV
10
5
0
40 mV
−5
0 100M 200M 300M 400M 500M 600M
NOISE FREQUENCY (Hz)
Figure 5. Remote Temperature Error vs.
Common-Mode Noise Frequency
30
20
10
D+ To GND
0
D+ To VCC
−10
−20
−30
−40
0
20 40 60 80
LEAKAGE RESISTANCE (MW)
100
Figure 4. Remote Temperature Error vs. PCB
Resistance
70
60
50
40
30
100 mV
20 40 mV 60 mV
10
0
−10
0
100M 200M 300M 400M 500M 600M
NOISE FREQUENCY (Hz)
Figure 6. Remote Temperature Error vs.
Differential-Mode Noise Frequency
1.20
1.18
1.16
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.00
0.98
3.0
3.1
3.2 3.3
3.4 3.5
VDD (V)
Figure 7. Normal IDDB B vs. Power Supply
3.6
15
10
5
100 mV
0
−5
250 mV
−10
−15
0
100M 200M 300M 400M 500M 600M
FREQUENCY (Hz)
Figure 8. Internal Temperature Error vs. Power
Supply Noise
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ADT7476A pdf, datenblatt
ADT7476A
Alert Response Address
Alert response address (ARA) is a feature of SMBus
devices, allowing an interrupting device to identify itself to
the host when multiple devices exist on the same bus.
The SMBALERT output can be used as either an interrupt
output or an SMBALERT. One or more outputs can be
connected to a common SMBALERT line connected to the
master. If a device’s SMBALERT line goes low, the
following procedure occurs:
1. SMBALERT is pulled low.
2. The master initiates a read operation and sends the
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
3. The device whose SMBALERT output is low
responds to the alert response address, and the
master reads its device address. The address of this
device is now known and can be interrogated per
usual.
4. If more than one device’s SMBALERT output is
low, the one with the lowest device address has
priority in accordance with normal SMBus
arbitration.
5. Once the ADT7476A responds to the alert
response address, the master must read the status
registers, and SMBALERT is cleared only if the
error condition goes away.
SMBus Timeout
The ADT7476A includes an SMBus timeout feature. If
there is no SMBus activity for 35 ms, the ADT7476A
assumes the bus is locked and releases the bus. This prevents
the device from locking or holding the SMBus expecting
data. Some SMBus controllers cannot handle the SMBus
timeout feature, so if necessary, it can be disabled.
Table 6. CONFIGURATION REGISTER 1 (REG. 0x40)
Bit Description
[6] TODIS
0: SMBus Timeout Enabled (Default)
1: SMBus Timeout Disabled
Virus Protection
To prevent rogue programs or viruses from accessing
critical ADT7476A register settings, the lock bit can be set.
Setting Bit 1 of Configuration Register 1 (0x40) sets the
lock bit and locks critical registers. In this mode, certain
registers can no longer be written to until the ADT7476A is
powered down and powered up again. For more information
on which registers are locked see Table 49.
Voltage Measurement Input
The ADT7476A has four external voltage measurement
channels. It can also measure its own supply voltage, VCC.
Pin 20 to Pin 23 can measure 5.0 V, 12 V, and 2.5 V
supplies, and the processor core voltage VCCP (0 V to 3 V
input). The VCC supply voltage measurement is carried out
through the VCC pin (Pin 4). The 2.5 V input can be used to
monitor a chipset supply voltage in computer systems.
Analog-to-Digital Converter
All analog inputs are multiplexed into the on-chip,
successive-approximation, analog-to-digital converter,
which has a resolution of 10 bits. The basic input range is 0 V
to 2.25 V, but the inputs have built-in attenuators to allow
measurement of 2.5 V, 3.3 V, 5.0 V, 12 V, and the processor
core voltage VCCP without any external components. To
allow the tolerance of these supply voltages, the ADC
produces an output of 3/4 full scale (768 dec or 300 hex) for
the nominal input voltage, giving it adequate headroom to
cope with overvoltages.
Input Circuitry
The internal structure for the analog inputs is shown in
Figure 24 The input circuit consists of an input protection
diode, an attenuator, plus a capacitor to form a first-order
low-pass filter that gives input immunity to high frequency
noise.
+12VIN
183.6 kW
30 kW
30 pF
+5VIN
93 kW
47 kW
30 pF
68 kW
VCC
71 kW
30 pF MUX
+2.5VIN
45 kW
94 kW
30 pF
VCCP
17.5 kW
52.5 kW
35 pF
Figure 24. Structure of Analog Inputs
Table 7. VOLTAGE MEASUREMENT REGISTERS
Register
Description
Default
0x20
0x21
0x22
0x23
0x24
2.5 V Reading
VCCP Reading
VCC Reading
5.0 V Reading
12 V Reading
0x00
0x00
0x00
0x00
0x00
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