EVAL-ADT7467EBZ ON Semiconductor, EVAL-ADT7467EBZ Datasheet - Page 19

• Manufacturer Part Number: EVAL-ADT7467EBZ
• Description: BOARD EVALUATION FOR ADT7467
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of EVAL-ADT7467EBZ

• Sensor Type: Temperature
• Sensing Range: -40°C ~ 120°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1.5°C
• Voltage - Supply: 3 V ~ 5.5 V
• Embedded: No
• Utilized Ic / Part: ADT7467
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Nulling Temperature Errors
As CPUs run faster, it is more difficult to avoid high frequency
clocks when routing the D+/D− traces around a system board.
Even when recommended layout guidelines are followed, some
temperature errors may still be attributed to noise coupled onto
the D+/D− lines. Constant high frequency noise usually attenuates
or increases temperature measurements by a linear, constant value.
The ADT7467 has temperature offset registers at Address 0x70
and Address 0x72 for the Remote 1 and Remote 2 temperature
channels, respectively. By performing a one-time calibration of
the system, the user can determine the offset caused by system
board noise and null it using the offset registers. The offset
registers automatically add an Offset 64/twos complement 8-bit
reading to every temperature measurement. The LSBs add
0.5°C offset to the temperature reading; therefore, the 8-bit
register effectively allows temperature offsets of up to ±64°C
with a resolution of 0.5°C. This ensures that the readings in the
temperature measurement registers are as accurate as possible.
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)
ADT7460/ADT7467 Backwards-Compatible Mode
By setting Bit 1 of Configuration Register 5 (0x7C), all tempera-
ture measurements are stored in the zone temperature value
registers (Register 0x25, Register 0x26, and Register 0x27) in
twos complement format in the range −128°C to +127°C. (The
ADT7468 makes calculations based on the Offset 64 extended
range and clamps the results if necessary.) The temperature
limits must be reprogrammed in twos complement format. 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, whereas the fault
condition is represented by −64°C = 0000 0000 in the extended
temperature range (−64°C to +191°C).
Figure 25. Measuring Temperature Using an NPN Transistor
Figure 26. Measuring Temperature Using a PNP Transistor
2N3904
2N3906
NPN
PNP
D+
D–
D+
D–
ADT7467
ADT7467
Rev. 3 | Page 19 of 77 | www.onsemi.com
Temperature Measurement Registers
Register 0x25 Remote 1 temperature = 0x01 default
Register 0x26 local temperature = 0x01 default
Register 0x27 Remote 2 temperature = 0x01 default
Register 0x77 Extended Resolution 2 = 0x00 default
Temperature Measurement Limit Registers
High and low limit registers are associated with each tempera-
ture measurement channel. Exceeding the programmed high or
low limit sets the appropriate status bit and can also generate
SMBALERT interrupts.
Register 0x4E Remote 1 temperature low limit = 0x01 default
Register 0x4F Remote 1 temperature high limit = 0x7F default
Register 0x50 local temperature low limit = 0x01 default
Register 0x51 local temperature high limit = 0x7F default
Register 0x52 Remote 2 temperature low limit = 0x01 default
Register 0x53 Remote 2 temperature high limit = 0x7F default
Reading Temperature from the ADT7467
It is important to note that temperature can be read from the
ADT7467 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 at any time and in no
particular order.
If the 10-bit measurement is required, this involves a 2-register
read for each measurement. The extended resolution register
(0x77) should be read first. Then all temperature reading
registers freeze until all temperature reading registers are read.
This prevents updating of an MSB reading while its two LSBs
are read and vice versa.
ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7467 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings are made internally, the results of which are averaged
and then placed into the value register. Sometimes it is necessary
to perform a very fast measurement. Setting Bit 4 of Configuration
Register 2 (0x73) turns averaging off.
<7:6> TDM2, Remote 2 temperature LSBs
<5:4> LTMP, local temperature LSBs
<3:2> TDM1, Remote 1 temperature LSBs
ADT7467