ADT7476A データシートの表示（PDF） - Analog Devices
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ADT7476A Datasheet PDF : 72 Pages
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ADT7476A
VOLTAGE MEASUREMENT REGISTERS
Register 0x20, 2.5 V Reading = 0x00 default
Register 0x21, VCCP Reading = 0x00 default
Register 0x22, VCC Reading = 0x00 default
Register 0x23, 5 V Reading = 0x00 default
Register 0x24, 12 V Reading = 0x00 default
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, VCCP Low Limit = 0x00 default
Register 0x47, VCCP High Limit = 0xFF default
Register 0x48, VCC Low Limit = 0x00 default
Register 0x49, VCC High Limit = 0xFF default
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, then the extended resolution register must be read
first, immediately followed by the appropriate voltage
measurement register.
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE
MEASUREMENTS
A number of other functions are available on the ADT7476A 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 Configuration Register 2
(0x73) turns averaging off. This effectively gives a reading 16
times faster but the reading can be noisier. The default round
robin cycle time takes 146.5 ms.
Table 6. Conversion Time with Averaging Disabled
Channel
Measurement Time (ms)
Voltage Channels
0.7
Remote Temperature 1
7
Remote Temperature 2
7
Local Temperature
1.3
When Bit 7 of Configuration Register 6 (0x10) is set, the default
round robin cycle time increases to 240 ms.
Bypass All Voltage Input Attenuators
Setting Bit 5 of Configuration Register 2 (0x73) removes the
attenuation circuitry from the 2.5 V, VCCP, VCC, 5 V, and 12 V
inputs. This 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.
Bypass Individual Voltage Input Attenuators
Bits [7:4] of Configuration Register 4 (0x7D) can be used
to bypass individual voltage channel attenuators.
Table 7. Bypassing Individual Voltage Input Attenuators
Configuration Register 4 (0x7D)
Bit
Channel Attenuated
4
Bypass 2.5 V attenuator
5
Bypass VCCP attenuator
6
Bypass 5 V attenuator
7
Bypass 12 V attenuator
Configuration Register 2 (0x73)
[4] = 1, averaging off.
[5] = 1, bypass input attenuators.
[6] = 1, single-channel convert mode.
TACH1 Minimum High Byte (0x55)
[7:5] Selects ADC channel for single-channel convert mode.
Rev. 0 | Page 16 of 72
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