adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 15

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

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.
2.
3.
4.
5.
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.
Configuration Register 1 (0x40)
[6] TODIS = 0, SMBus timeout enabled (default).
[6] TODIS = 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 18.
SMBALERT is pulled low.
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.
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.
If more than one device’s SMBALERT output is low, the
one with the lowest device address has priority in accor-
dance with normal SMBus arbitration.
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.
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VOLTAGE MEASUREMENT INPUT
The ADT7476A has four external voltage measurement
channels. It can also measure its own supply voltage, V
Pin 20 to Pin 23 can measure 5 V, 12 V, and 2.5 V supplies,
and the processor core voltage V
supply voltage measurement is carried out through the V
(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 V, 12 V, and the processor core voltage V
without any external components. To allow the tolerance of
these supply voltages, the ADC produces an output of ¾ 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.
3.3V
2.5V
12V
V
5V
CCP
IN
IN
IN
IN
Figure 24. Structure of Analog Inputs
17.5kΩ
120kΩ
93kΩ
68kΩ
45kΩ
52.5kΩ
20kΩ
47kΩ
71kΩ
94kΩ
CCP
(0 V to 3 V input). The V
30pF
30pF
30pF
30pF
35pF
MUX
ADT7476A
CC
CCP
.
CC
pin
CC