Input Circuitry; Voltage Measurement Registers; Vccp Limit Registers; Extended Resolution Registers - Analog Devices dBCool ADT7475 Manual

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 fre-
quency noise.
17.5kΩ
V
CCP
52.5kΩ
Figure 20. Structure of Analog Inputs

VOLTAGE MEASUREMENT REGISTERS

Reg. 0x21 V Reading = 0x00 default
CCP
Reg. 0x22 V Reading = 0x00 default
CC
V LIMIT REGISTERS
CCP
Associated with the V measurement channel is a high and
CCP
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. 0x46 V Low Limit = 0x00 default
CCP
Reg. 0x47 V High Limit = 0xFF default
CCP
Table 5 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 (0x20 to 0x 24) 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.
analog input is shown in
CCP
35pF
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 actually 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 (Reg. 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 (Reg. 0x73) removes
the attenuation circuitry from the V
the user 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 (Reg. 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 4. Single Channel ADC Conversion
Bits <7:5> Reg. 0x55
001
010
101
110
111
Configuration Register 2 (Reg. 0x73)
<4> = 1, averaging off.
<5> = 1, bypass input attenuators.
<6> = 1, single channel convert mode.
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> selects ADC channel for single channel convert mode.
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ADT7475
input. This allows
CCP
Channel Selected
V
CCP
V
CC
Remote 1 Temperature
Local Temperature
Remote 2 Temperature