ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 16

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7468
ANALOG-TO-DIGITAL CONVERTER
All analog inputs are multiplexed into the on-chip, successive
approximation, analog-to-digital converter, which has a resolu-
tion 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
external components. To allow for the tolerance of these supply
voltages, the ADC produces an output of 3/4 full scale (decimal
768 or 300 hex) for the nominal input voltage and therefore has
adequate headroom to cope with overvoltages.
VOLTAGE MEASUREMENT INPUT
The ADT7468 has four external voltage measurement channels
and can measure its own supply voltage, V
measure 5 V, 12 V, 2.5 V supplies, and the processor core voltage
V
carried out through the V
uration Register 1 (Reg. 0x40) allows a 5 V supply to power the
ADT7468 and be measured without overranging the V
measurement channel. The 2.5 V input can be used to monitor
a chipset supply voltage in computer systems.
Input Circuitry
The internal structure for the analog inputs is shown in
Figure 22. 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
Reg. 0x20, 2.5 V reading = 0x00 default
Reg. 0x21, V
Reg. 0x22, V
Reg. 0x23, 5 V reading = 0x00 default
Reg. 0x24, 12 V reading = 0x00 default
CCP
(0 V to 3 V input). The V
3.3V
2.5V
12V
V
5V
CCP
CCP
CC
IN
IN
IN
IN
reading = 0x00 default
reading = 0x00 default
Figure 22. Structure of Analog Inputs
17.5kΩ
120kΩ
93kΩ
68kΩ
45kΩ
52.5kΩ
20kΩ
47kΩ
71kΩ
94kΩ
CC
pin (Pin 4). Setting Bit 7 of Config-
CC
supply voltage measurement is
30pF
30pF
30pF
30pF
35pF
CC
. Pins 20 to 23 can
MUX
CCP
without any
CC
Rev. A | Page 16 of 84
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.
Reg. 0x44, 2.5 V low limit = 0x00 default
Reg. 0x45, 2.5 V high limit = 0xFF default
Reg. 0x46, V
Reg. 0x47, V
Reg. 0x48, V
Reg. 0x49, V
Reg. 0x4A, 5 V low limit = 0x00 default
Reg. 0x4B, 5 V high limit = 0xFF default
Reg. 0x4C, 12 V Low Limit = 0x00 default
Reg. 0x4D, 12 V High Limit = 0xFF default
Table 6 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.
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE
MEASUREMENTS
A number of other functions are available on the ADT7468 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each voltage measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value register. For
instance, where faster conversions are needed, setting Bit 4 of
Configuration Register 2 (Reg. 0x73) turns averaging off. This
effectively gives a reading 16 times faster (0.7 ms), but the
reading may be noisier.
Bypass Voltage Input Attenuator
Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes
the attenuation circuitry from the 2.5 V, V
V inputs, which allows the user to directly connect external
sensors or rescale the analog voltage measurement inputs for
other applications. The input range of the ADC without the
attenuators is 0 V to 2.25 V.
CCP
CCP
CC
CC
low limit = 0x00 default
high limit = 0xFF default
low limit = 0x00 default
high limit = 0xFF default
CCP
, V
CC
, 5 V, and 12