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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.
Table 8. VOLTAGE LIMIT REGISTERS
Register
0x44
0x45
0x46
0x47
0x48
0x49
0x4A
0x4B
0x4C
0x4D
Table 13 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.
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Description
Default
2.5 V Low Limit
0x00
2.5 V High Limit
0xFF
V
Low Limit
0x00
CCP
V
High Limit
0xFF
CCP
V
Low Limit
0x00
CC
V
High Limit
0xFF
CC
5.0 V Low Limit
0x00
5.0 V High Limit
0xFF
12 V Low Limit
0x00
12 V High Limit
0xFF
ADT7476A
Table 9. CONVERSION TIME WITH AVERAGING
DISABLED
Channel
Voltage Channels
Remote Temperature 1
Remote Temperature 2
Local Temperature
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, 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 10. BYPASSING INDIVIDUAL VOLTAGE INPUT
ATTENUATORS
Configuration Register 4 (0x7D)
Bit No.
[4]
Bypass 2.5 V Attenuator
[5]
Bypass V
[6]
Bypass 5.0 V Attenuator
[7]
Bypass 12 V Attenuator
Table 11. CONFIGURATION REGISTER 2 (REG. 0x73)
Bit
[4]
[5]
[6]
TACH1 Minimum High Byte (0x55)
[7:5] Selects ADC channel for single-channel convert mode.
Single-channel ADC Conversion
While single-channel mode is intended as a test mode that
can be used to increase sampling times for a specific
channel, and therefore helps to analyze that channel's
performance in greater detail, it can also have other
applications.
Setting Bit 6 of Configuration Register 2 (0x73) places
the ADT7476A into single-channel ADC conversion mode.
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13
Measurement Time (ms)
0.7
7
7
1.3
CCP
Channel Attenuated
Attenuator
CCP
Description
1: Averaging Off
1: Bypass Input Attenuators
1: Single-channel Convert Mode
, V
, 5.0 V,
CC
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