ADT7470 datasheet(16/41 Pages) AD

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Data Sheet

ADT7470

Rev. E | Page 15 of 40

TEMPERATURE MEASUREMENT LIMITS

High and low temperature limits can be individually set for

each of the TMP05/06s that the ADT7470 is monitoring. The

temperature limit registers are at address 0x44 to 0x57. The

power-on default value for all TMP05/06 lower limits is −127°C

(0x81). The power –on default value for all TMP05/06 upper

limits is +127°C (0x7F). See Table 9 for details on the

temperature limit registers.

If the temperature measured from a TMP05/06 exceeds the

upper or lower limit, then a status bit in the Interrupt Status

registers will be set to 1. See Table 12 and Table 13 for more

details on the temperature status bits.

SMBALERT will assert is any temperature exceeds either the

upper or lower limits. The temperature measurements can be

masked as interrupt sources for SMBALERT using the interrupt

mask registers, 0x72 and 0x73. See Table 14 and Table 15 for

more details on the interrupt mask registers.

THERMAL ZONES FOR AUTOMATIC FAN CONTROL

The ADT7470 can control up to four independent thermal zones

with individual fans. The user can configure which TMP05

controls which fan via register 0x7C and 0x7D.For each of the four

thermal zones, an individual TMP05, or the hottest TMP05 in the

daisy chain, can control the fan. In a system with n TMP05s, it is

possible to have 1 or n TMP05s controlling each fan.

Thermal Zone TMIN

For each of the four thermal zones, the user can configure the

minimum temperature at which the fans run. Registers 0x6E to

0x71 should be configured with the minimum temperature for

each thermal zone. When the temperature exceeds TMIN for that

thermal zone, the fans run at minimum speed (PWMMIN). The

fan speed increases to maximum speed (PWMMAX) at [TMIN +

20°C]. Fan on/off hysteresis is set at 4°C so that the fans turn off

4°C below the temperature at which they turn on. This prevents

fan chatter in the system.

ADT7470 Datasheet(PDF) 16 Page - Analog Devices