ADT7468ARQ Ver la hoja de datos (PDF) - Analog Devices
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ADT7468ARQ Datasheet PDF : 80 Pages
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ADT7468
PRODUCT DESCRIPTION
The ADT7468 is a complete thermal monitor and multiple fan
controller for any system requiring thermal monitoring and
cooling. The device communicates with the system via a serial
system management bus. The serial bus controller has a serial
data line for reading and writing addresses and data (Pin 1), and
an input line for the serial clock (Pin 2). All control and
programming functions for the ADT7468 are performed over
the serial bus. In addition, a pin can be reconfigured as an
SMBALERT output to signal out-of-limit conditions.
COMPARISON BETWEEN ADT7463 AND ADT7468
The ADT7468 is an upgrade to the ADT7463. The ADT7468
and ADT7463 are almost pin and register map compatible. The
ADT7468 and ADT7463 have the following differences:
1. On the ADT7468, the PWM drive signals can be config-
ured as either high frequency or low frequency drives. The
low frequency option is programmable between 10 Hz and
100 Hz. The high frequency option is 22.5 kHz. On the
ADT7463, only the low frequency option is available.
2. Once the VCC is powered up, monitoring of temperature
and fan speeds is enabled on the ADT7468 when VCCP is
powered up, or if VCCP is never powered up, when the first
SMBus transaction with the ADT7468 is completed. On the
ADT7463, the STRT bit in Configuration Register 1 must
be set to enable monitoring.
3. The fans are switched off by default on power-up on the
ADT7468. On the ADT7463, the fans run at full speed on
power-up.
Fail-safe cooling is provided on the ADT7468 in that, if the
measured temperature exceeds the THERM limit (100°C),
the fans run at full speed.
Fail-safe cooling is also provided 4.6 s after VCCP is powered
up. See Figure 48. The fans go to full speed, if the ADT7468
has not been addressed via the SMBus within 4.6 s of when
the VCCP is powered up. This protects the system in the
event that the SMBus fails. The ADT7468 can be pro-
grammed at any time, either before or after the 4.6 s has
elapsed, and it behaves as programmed. If VCCP is never
powered up, fail-safe cooling is effectively disabled. If VCCP
is disabled, writing to the ADT7468 at any time causes the
ADT7468 to operate normally.
4. Series resistance cancellation (SRC) is provided on the
remote temperature channels on the ADT7468, but not on
the ADT7463. SRC automatically cancels linear offset
introduced by a series resistance between the thermal
diode and the sensor.
5. The ADT7468 has an extended temperature measurement
range. The measurement range goes from–64°C to +191°C.
On the ADT7463, the measurement range is from −127°C
to +127°C. This means that the ADT7468 can measure
higher temperatures. The ADT7468 also includes the
ADT7463 temperature range; the temperature measure-
ment range can be switched by setting Bit 0 of
Configuration Register 5.
6. The ADT7468 maximum fan speed (% duty cycle) in the
automatic fan speed control loop can be programmed. The
maximum fan speed is 100% duty cycle on the ADT7463
and is not programmable.
7. The offset register in the ADT7468 is programmable up to
±64°C with 0.50°C resolution. The offset register of the
ADT7463 is programmable up to ±32°C with 0.25°C
resolution.
8. VCCP is monitored on Pin 23 of the ADT7468 and can be
used to set the threshold for THERM (PROCHOT) (2/3 of
VCCP). The threshold for THERM (PROCHOT) is set at
VIH = 1.7 V and VIL = 0.8 V on the ADT7463.
9. On the ADT7463, Pin 22 can be reconfigured as SMBus
ALERT. This is not available on the ADT7468; instead,
SMBALERT can be enabled on Pin 14.
10. A GPIO can also be made available on Pin 14 on the
ADT7468. This is not available on the ADT7463. Set the
GPIO polarity and direction in Configuration Register 5.
The GPIO status bit is Bit 5 of Status Register 2 (shared
with TACH4 and THERM, because only one can be
enabled at a time).
11. The ADT7463 has three possible SMBus addresses, which
are selectable using the address select and address enable
pins. The ADT7468 has one SMBus address available at
Address 0x2E.
Due to the inclusion of extra functionality, the register map has
changed, including an additional configuration register:
Configuration Register 5 at Address 0x7C.
Configuration Register 5
Bit 0: If Bit 0 is set to 1, the ADT7468 is backward compatible
temperature-wise with the ADT7463. Measurements, TMIN
calibration circuit, fan control, etc., work in the range −127°C to
+127°C. Also, care should be taken in reprogramming the
temperature limits (TMIN, operating point, THERM limits) to
their desired twos complement value, because the power-on
default for them is at Offset 64. The extended temperature range
is −64°C to 191°C. The default is 1, which is in the −64°C to
+191°C temperature range.
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