Input Circuitry; Voltage Measurement Registers; Vccp Limit Registers; Additional Adc Functions For Voltage Measurements - Analog Devices dBCool ADT7467 Manual

ADT7467

INPUT CIRCUITRY

The internal structure for the V
Figure 22. The input circuit consists of an input protection
diode, an attenuator, plus a capacitor to form a first-order low-
pass filter that gives the input immunity to high frequency
noise.
17.5kΩ
V
CCP
52.5kΩ
Figure 22. 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 and V
CCP
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. 0x46 V Low Limit = 0x00 default
CCP
Reg. 0x47 V High Limit = 0xFF default
CCP
Reg. 0x48 VCC Low Limit = 0x00 default
Reg. 0x49 VCC High Limit = 0xFF default
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 0.7 ms and averages 16 conversions to reduce noise; a
measurement takes nominally 11 ms.
analog input is shown in
CCP
35pF
measurement channels is a
CC
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE
MEASUREMENTS
A number of other functions are available on the ADT7467 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 (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 V
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
ADT7467 into single-channel ADC conversion mode. In this
mode, the ADT7467 can be made to read a single voltage
channel only. If the internal ADT7467 clock is used, the selected
input is read every 0.7 ms. The appropriate ADC channel is
selected by writing to Bits <7:5> of the TACH1 minimum high
byte register (0x55).
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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input. This allows the
CCP
Channel Selected
V
CCP
V
CC
Remote 1 Temperature
Local Temperature
Remote 2 Temperature