ADT7476AARQZ 查看數據表（PDF） - ON Semiconductor
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ADT7476AARQZ Datasheet PDF : 67 Pages
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ADT7476A
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (0x73) places the
ADT7476A into single-channel ADC conversion mode. In
this mode, the ADT7476A can be made to read a single
temperature channel only. The appropriate ADC channel is
selected by writing to Bits [7:5] of the TACH1 minimum
high byte register (0x55).
Table 10. Programming Single−Channel ADC Mode
for Temperatures
Bits [7:5], Register 0x55
101
110
111
Channel Selected
Remote 1 Temperature
Local Temperature
Remote 2 Temperature
Configuration Register 2 (0x73)
[4] = 1, averaging off.
[6] = 1, single-channel convert mode.
TACH1 Minimum High Byte (0x55)
[7:5] selects ADC channel for single-channel convert mode.
Overtemperature Events
Overtemperature events on any of the temperature
channels can be detected and dealt with automatically in
automatic fan speed control mode. Register 0x6A to
Register 0x6C are the THERM temperature limits. When a
temperature exceeds its THERM temperature limit, all
PWM outputs run at the maximum PWM duty cycle
(Register 0x38, Register 0x39, and Register 0x3A).
This effectively runs the fans at the fastest allowed speed.
The fans run at this speed until the temperature drops
below THERM minus hysteresis. This can be disabled by
setting Bit 2, the boost bit, in Configuration Register 3
(0x78). The hysteresis value for the THERM temperature
limit is the value programmed into the hysteresis registers
(0x6D and 0x6E). The default hysteresis value is 4°C.
THERM LIMIT
TEMPERATURE
HYSTERESIS (°C)
FANS
100%
Figure 28. THERM Temperature Limit Operation
THERM can be disabled on specific temperature channels
using Bits [7:5] of Configuration Register 5 (0x7C).
THERM can also be disabled by:
• Writing −64°C to the appropriate THERM temperature
limit in Offset 64 mode.
• Writing −128°C to the appropriate THERM
temperature limit in twos complement mode.
Limits, Status Registers, and Interrupts
Limit Values
Associated with each measurement channel on the
ADT7476A are high and low limits. These can form the
basis of system status monitoring; a status bit can be set for
any out-of-limit condition and is detected by polling the
device. Alternatively, SMBALERT interrupts can be
generated to flag out-of-limit conditions to a processor
or microcontroller.
8-Bit Limits
The following is a list of 8-bit limits on the ADT7476A.
Voltage Limit Registers
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, 5.0 V Low Limit = 0x00 default
Register 0x4B, 5.0 V High Limit = 0xFF default
Register 0x4C, 12 V Low Limit = 0x00 default
Register 0x4D, 12 V High Limit = 0xFF default
Temperature Limit Registers
Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default
Register 0x4F, Remote 1 Temperature High Limit = 0x7F
default
Register 0x6A, Remote 1 THERM Limit = 0x64 default
Register 0x50, Local Temperature Low Limit = 0x81 default
Register 0x51, Local Temperature High Limit = 0x7F default
Register 0x6B, Local THERM Limit = 0x64 default
Register 0x52, Remote 2 Temperature Low Limit = 0x81 default
Register 0x53, Remote 2 Temperature High Limit = 0x7F
default
Register 0x6C, Remote 2 THERM Limit = 0x64 default
THERM Timer Limit Register
Register 0x7A, THERM Timer Limit = 0x00 default.
16-Bit Limits
The fan TACH measurements are 16-bit results. The fan
TACH limits are also 16 bits, consisting of a high byte and
low byte. Because fans running under speed or stalled are
normally the only conditions of interest, only high limits
exist for fan TACHs. Because the fan TACH period is
actually being measured, exceeding the limit indicates a
slow or stalled fan.
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