ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 13

• Manufacturer Part Number: ADT7475
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

INPUT CIRCUITRY
The internal structure for the V
Figure 20. The input circuit consists of an input protection
diode, an attenuator, and a capacitor to form a first-order, low-
pass filter that gives the input immunity to high frequency noise.
VOLTAGE MEASUREMENT REGISTERS
Register 0x21, V
Register 0x22, V
V
Associated with the V
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 0x46, V
Register 0x47, V
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 711 μs and averages 16 conversions to reduce noise; a
measurement takes nominally 11.38 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 is locked until their
data is read. That is, if extended resolution is required, then the
extended resolution register must be read first, immediately
followed by the appropriate voltage measurement register.
CCP
LIMIT REGISTERS
V
CCP
CC
CCP
CCP
CCP
Figure 20. Structure of Analog Inputs
Reading = 0x00 default
Reading = 0x00 default
Low Limit = 0x00 default
High Limit = 0xFF default
CCP
17.5kΩ
measurement channel is a high and
52.5kΩ
CCP
analog input is shown in
35pF
Rev. B | Page 13 of 68
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE
MEASUREMENTS
A number of other functions are available on the ADT7475 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each voltage measurement read from a value register,
16 readings have been made internally, and the results averaged,
before being placed into the value register. For instances where
faster conversions are needed, setting Bit 4 of Configuration
Register 2 (0x73) turns averaging off. This effectively gives a
reading 16 times faster (711 μs), but the reading may be noisier.
Bypass Voltage Input Attenuator
Setting Bit 5 of Configuration Register 2 (0x73) removes the
attenuation circuitry from the V
to directly connect external sensors or to 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.
Single-Channel ADC Conversion
Setting Bit 6 of Configuration Register 2 (0x73) places the
ADT7475 into single-channel ADC conversion mode. In this
mode, the ADT7475 can be made to read a single voltage chan-
nel only. If the internal ADT7475 clock is used, the selected
input is read every 711 μs. The appropriate ADC channel is
selected by writing to Bits [7:5] of the TACH1 minimum high
byte register (0x55).
Table 5. Single-Channel ADC Conversion
Register 0x55, Bits [7:5]
001
010
101
110
111
Configuration Register 2 (0x73)
Bit 4 = 1; averaging off.
Bit 5 = 1; bypass input attenuators.
Bit 6 = 1; single-channel convert mode.
TACH1 Minimum High Byte (0x55)
Bits [7:5] select the ADC channel for single-channel convert mode.
CCP
Channel Selected
V
V
Remote 1 temperature
Local temperature
Remote 2 temperature
input. This allows the user
CCP
CC
ADT7475