EVAL-ADT7463EB ON Semiconductor, EVAL-ADT7463EB Datasheet - Page 18

• Manufacturer Part Number: EVAL-ADT7463EB
• Manufacturer: ON Semiconductor

Specifications of EVAL-ADT7463EB

• Lead Free Status / RoHS Status: Supplier Unconfirmed

ADT7463
Temperature Measurement Registers
Reg. 0x25 Remote 1 Temperature = 0x80 Default
Reg. 0x26 Local Temperature = 0x80 Default
Reg. 0x27 Remote 2 Temperature = 0x80 Default
Reg. 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 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.
Reg. 0x4E Remote 1 Temp Low Limit = 0x81 Default
Reg. 0x4F Remote 1 Temp High Limit = 0x7F Default
Reg. 0x50 Local Temp Low Limit = 0x81 Default
Reg. 0x51 Local Temp High Limit = 0x7F Default
Reg. 0x52 Remote 2 Temp Low Limit = 0x81 Default
Reg. 0x53 Remote 2 Temp High Limit = 0x7F Default
Reading Temperature from the ADT7463
It is important to note that temperature can be read from the
ADT7463 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. The extended resolution register
(Reg. 0x77) should be read first. This causes all temperature
reading registers to be frozen until all temperature reading regis-
ters have been read from. This prevents an MSB reading from
being updated while its 2 LSBs are being read and vice versa.
ADDITIONAL ADC FUNCTIONS
A number of other functions are available on the ADT7463 to
offer the systems 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 may be necessary to take a very fast measurement, e.g., of CPU
temperature. Setting Bit 4 of Configuration Register 2 (Reg. 0x73)
turns averaging off. This takes a reading every 13 ms. The mea-
surement itself takes 4 ms.
–18–
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADT7463 into single-channel ADC conversion mode. In this
mode, the ADT7463 can be made to read a single temperature
channel only. If the internal ADT7463 clock is used, the
selected input is read every 1.4 ms. The appropriate ADC chan-
nel is selected by writing to Bits <7:5> of TACH1 Minimum
High Byte Register (0x55).
Bits <7:5> Reg 0x55
101
110
111
Configuration Register 2 (Reg. 0x73)
<4> = 1 Averaging Off
<6> = 1 Single-Channel Convert Mode
TACH1 Minimum High Byte (Reg. 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. Registers 0x6A to 0x6C are the THERM limits.
When a temperature exceeds its THERM limit, all fans run at
100% duty cycle. The fans stay running at 100% until the
temperature drops below THERM – Hysteresis (this can be
disabled by setting the boost bit in Configuration Register 3,
Bit 2, Register 0x78). The hysteresis value for that THERM
limit is the value programmed into Registers 0x6D, 0x6E
(hysteresis registers). The default hysteresis value is 4°C.
THERM LIMIT
FANS
TEMPERATURE
Figure 16. THERM Limit Operation
100%
Channel Selected
Remote 1 Temperature
Local Temperature
Remote 2 Temperature
HYSTERESIS ( C)
REV. C