ADT7468 datasheet(21/80 Pages) AD

21 / 80 page

ADT7468

Rev. 0 | Page 21 of 80

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 Temperature Low Limit = 0x01 default

Reg. 0x4F, Remote 1 Temperature High Limit = 0x7F default

Reg. 0x50, Local Temperature Low Limit = 0x01 default

Reg. 0x51, Local Temperature High Limit = 0x7F default

Reg. 0x52, Remote 2 Temperature Low Limit = 0x01 default

Reg. 0x53, Remote 2 Temperature High Limit = 0x7F default

Reading Temperature from the ADT7468

It is important to note that temperature can be read from the

ADT7468 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

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 ADT7468 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 (Reg. 0x73) turns averaging off.

Table 8. Conversion Time with Averaging Disabled

Channel

Measurement Time

Voltage Channels

0.7 ms

Remote Temperature 1

7 ms

Remote Temperature 2

7 ms

Local Temperature

1.3 ms

Table 9. Conversion Time with Averaging Enabled

Channel

Measurement Time

Voltage Channels

11 ms

Remote Temperature

39 ms

Local Temperature

12 ms

Single-Channel ADC Conversions

Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the

ADT7468 into single-channel ADC conversion mode. In this

mode, the ADT7468 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. Channel Selection

Bits <7:5> Reg. 0x55

Channel Selected

101

Remote 1 temperature

110

Local temperature

111

Remote 2 temperature

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. 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 (Reg. 0x38, Reg. 0x39, and Reg. 0x3A). This

effectively runs the fans at the fastest allowed speed. The fans

stay running at this speed until the temperature drops below

THERM minus hysteresis. (This can be disabled by setting the

boost bit in Configuration Register 3, Bit 2, Reg. 0x78.) The

hysteresis value for that THERM temperature limit is the value

programmed into Reg. 0x6D and Reg. 0x6E (hysteresis

registers). The default hysteresis value is 4°C.

FANS

TEMPERATURE

100%

HYSTERESIS (°C)

THERM LIMIT

Figure 27. THERM Temperature Limit Operation

ADT7468 Datasheet(PDF) 21 Page - Analog Devices

ADT7468 Datasheet(HTML) 21 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Datasheet Download

Link URL