adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 21

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adt7476a

Manufacturer Part Number
adt7476a
Description
Dbcool Remote Thermal Controller And Voltage Monitor
Manufacturer
Analog Devices, Inc.
Datasheet

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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/ADT7476A Backwards Compatible Mode
By setting Bit 0 of Configuration Register 5 (0x7C), all tempera-
ture measurements are stored in the zone temperature reading
registers (0x25, 0x26, and 0x27) in twos complement in the
−63°C to +127°C range. The temperature limits must be
reprogrammed in twos complement.
If a twos complement temperature below −63°C is entered, the
temperature is clamped to −63°C. In this mode, the diode fault
condition remains −128°C = 1000 0000, while in the extended
temperature range (−63°C to +191°C), the fault condition is
represented by −64°C = 0000 0000.
Temperature Reading Registers
Register 0x25, Remote 1 Temperature
Register 0x26, Local Temperature
Register 0x27, Remote 2 Temperature
Register 0x77, Extended Resolution 2 = 0x00 default
[7:6] TDM2, Remote 2 temperature LSBs.
[5:4] LTMP, Local temperature LSBs.
[3:2] TDM1, Remote 1 temperature LSBs.
Temperature 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. 0 | Page 21 of 72
Reading Temperature from the ADT7476A
It is important to note that temperature can be read from the
ADT7476A 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 2-register
read for each measurement. 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 ADT7476A 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 12. 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 13. Conversion Time with Averaging Enabled
Channel
Voltage Channels
Remote Temperature
Local Temperature
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 14. Programming Single Channel ADC Mode for
Temperatures
Bits [7:5] Reg. 0x55
101
110
111
Channel Selected
Remote 1 temperature
Local temperature
Remote 2 temperature
Measurement Time (ms)
0.7
7
7
1.3
Measurement Time (ms)
11
39
12
ADT7476A

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