ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 18

• Manufacturer Part Number: ADT7475
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7475
Changing Bit 1 of Configuration Register 5 (0x7C) changes the
resolution and therefore the range of the temperature offset as
either having a range of –63°C to +127°C, with a resolution of
1°C, or having a range of −63°C to +64°C, with a resolution of
0.5°C. This temperature offset can be used to compensate for
linear temperature errors introduced by noise.
Temperature Offset Registers
Register 0x70, Remote 1 Temperature Offset = 0x00 (0°C default)
Register 0x71, Local Temperature Offset = 0x00 (0°C default)
Register 0x72, Remote 2 Temperature Offset = 0x00 (0°C default)
ADT7463/ADT7475 Backwards Compatible Mode
By setting Bit 0 of Configuration Register 5 (0x7C), all tempera-
ture measurements are stored in the zone temperature value
registers (0x25, 0x26, and 0x27) in twos complement in the
range −128°C to +127°C. The temperature limits must be
reprogrammed in twos complement.
If a twos complement temperature below −128°C is entered, the
temperature is clamped to −128°C. In this mode, the diode fault
condition remains −128°C = 1000 0000, while in the extended
temperature range (−64°C to +191°C), the fault condition is
represented by −64°C = 0000 0000.
Temperature Measurement Registers
Register 0x25, Remote 1 Temperature
Register 0x26, Local Temperature
Register 0x27, Remote 2 Temperature
Register 0x77, Extended Resolution 2 = 0x00 default
Bits [7:6] TDM2, Remote 2 temperature LSBs.
Bits [5:4] LTMP, local temperature LSBs.
Bits [3:2] TDM1, Remote 1 temperature LSBs.
Temperature Measurement Limit Registers
Associated with each temperature measurement channel are high
and low limit registers. Exceeding the programmed high or low
limit causes the appropriate status bit to be set. Exceeding either
limit can also generate SMBALERT interrupts (depending on the
way the interrupt mask register is programmed and assuming
that SMBALERT is set as an output on the appropriate pin).
Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default
Register 0x4F, Remote 1 Temperature High Limit = 0x7F default
Register 0x50, Local Temperature Low Limit = 0x81 default
Register 0x51, Local Temperature High Limit = 0x7F default
Register 0x52, Remote 2 Temperature Low Limit = 0x81 default
Register 0x53, Remote 2 Temperature High Limit = 0x7F default
Rev. B | Page 18 of 68
Reading Temperature from the ADT7475
It is important to note that temperature can be read from the
ADT7475 as an 8-bit value (with 1°C resolution) or as a 10-bit
value (with 0.25°C resolution). If only 1°C resolution is required,
the temperature readings can be read back at any time and in no
particular order.
If the 10-bit measurement is required, this involves a two-
register read for each measurement. The Extended Resolution
Register 2 (0x77) should be read first. This causes all
temperature reading registers to be frozen until all temperature
reading registers have been read from. This prevents an MSB
reading from being updated while its two LSBs are being read
and vice versa.
ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7475 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings have actually been made internally, and the results
averaged, before being placed into the value register. Sometimes
it is necessary to take a very fast measurement. Setting Bit 4 of
Configuration Register 2 (0x73) turns averaging off. The default
round-robin cycle time takes 146.5 ms.
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.
Table 10. Conversion Time with Averaging Enabled
Channel
Voltage Channels
Remote Temperature 1
Remote Temperature 2
Local Temperature
Measurement Time (ms)
11
39
39
12
Measurement Time (ms)
0.7
7
7
1.3