Datasheet

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 T
MIN
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 T
MIN
for that
thermal zone, the fans run at minimum speed (PWM
MIN
). The
fan speed increases to maximum speed (PWM
MAX
) at [T
MIN
+
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.