ADT7476 Analog Devices, Inc., ADT7476 Datasheet - Page 17

• Manufacturer Part Number: ADT7476
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

VOLTAGE MEASUREMENT INPUT
The ADT7476 has four external voltage measurement channels.
It can also measure its own supply voltage, V
can measure 5 V, 12 V, and 2.5 V supplies and the processor
core voltage V
measurement is carried out through the V
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. This 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
nal 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 and, therefore, has adequate
headroom to deal 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, and a capacitor to form a first-order low-
pass filter that gives input immunity to high frequency noise.
VOLTAGE MEASUREMENT REGISTERS
Register 0x20, 2.5 V Measurement = 0x00 default
Register 0x21, V
Register 0x22, V
Register 0x23, 5 V Measurement = 0x00 default
Register 0x24, 12 V Measurement = 0x00 default
3.3V
2.5V
12V
V
5V
CCP
IN
IN
IN
IN
CCP
CCP
CC
Figure 24. Structure of Analog Inputs
(0 V to 3 V input). The V
Measurement = 0x00 default
Measurement = 0x00 default
17.5kΩ
120kΩ
93kΩ
68kΩ
45kΩ
52.5kΩ
20kΩ
47kΩ
71kΩ
94kΩ
30pF
30pF
30pF
30pF
35pF
CCP
CC
CC
without any exter-
CC
pin (Pin 4). The
supply voltage
MUX
. Pin 20 to Pin 23
Rev. B | Page 17 of 72
VOLTAGE LIMIT REGISTERS
Associated with each voltage measurement channel is a high
and low limit register. Exceeding the programmed high or low
limit causes the appropriate status bit to be set. Exceeding either
limit can also generate SMBALERT interrupts.
Register 0x44, 2.5 V Low Limit = 0x00 default
Register 0x45, 2.5 V High Limit = 0xFF default
Register 0x46, V
Register 0x47, V
Register 0x48, V
Register 0x49, V
Register 0x4A, 5 V Low Limit = 0x00 default
Register 0x4B, 5 V High Limit = 0xFF default
Register 0x4C, 12 V Low Limit = 0x00 default
Register 0x4D, 12 V High Limit = 0xFF default
Table 9 shows the input ranges of the analog inputs and output
codes of the 10-bit ADC.
When the ADC is running, it samples and converts a voltage
input in 0.7 ms and averages 16 conversions to reduce noise; a
measurement takes nominally 11 ms.
EXTENDED RESOLUTION REGISTERS
Voltage measurements can be made with higher accuracy using
the extended resolution registers (0x76 and 0x77). Whenever
the extended resolution registers are read, the corresponding
data in the voltage measurement registers (0x20 to 0x24) is
locked until their data is read. That is, if extended resolution is
required, the extended resolution register must be read first
immediately followed by the appropriate voltage measurement
register.
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE
MEASUREMENTS
Several other functions are available on the ADT7476 to offer
the system designer increased flexibility.
Turn-Off Averaging
For each voltage/temperature measurement read from a value
register, 16 readings have been made internally and the results
averaged before being placed into the value register. When faster
conversions are needed, setting Bit 4 of Configura-tion Register 2
(0x73) turns averaging off. This effectively gives a reading that is
16 times faster, but the reading can be noisier. The default round-
robin cycle time is 146.5 ms.
CCP
CCP
CC
CC
Low Limit = 0x00 default
High Limit = 0xFF default
Low Limit = 0x00 default
High Limit = 0xFF default
ADT7476