參數(shù)資料
型號(hào)： LM64
廠商： National Semiconductor Corporation
元件分類： 溫度/濕度傳感器
英文描述： 【1∑C Remote Diode Temperature Sensor with PWM Fan Control and 5 GPIO’s
中文描述： 【1ΣC遠(yuǎn)程二極管溫度傳感器，PWM風(fēng)扇控制和5個(gè)GPIO的
文件頁(yè)數(shù)： 9/29頁(yè)
文件大?。?/td> 363K
代理商： LM64
1.0 Functional Description
The LM64 Remote Diode Temperature Sensor with Inte-
grated Fan Control incorporates a
V
-based temperature
sensor using a Local or Remote diode and a 10-bit plus sign
Σ
ADC (Delta-Sigma Analog-to-Digital Converter). The
pulse-width modulated (PWM) open-drain output, with a
pull-up resistor, can drive a switching transistor to modulate
the fan. The LM64 can measure the fan speed on the pulses
from the fan’s open-collector tachometer output, pulled up by
a 1.5 k
resistor to V
. The ALERT open-drain output will
be pulled low under certain conditions descibed in the sec-
tions below. The T_Crit open-drain output will be pulled low
when the T_Crit setpoint temperature limit is exceeded. This
behaves as a typical comparator function without any latch-
ing.
The LM64’s two-wire interface is compatible with the SMBus
Specification 2.0 . For more information the reader is di-
rected to
www.smbus.org
.
In the LM64, digital comparators are used to compare the
measured Local Temperature (LT) to the Local High Setpoint
user-programmable temperature limit register. The mea-
sured Remote Temperature (RT) is digitally compared to the
Remote High Setpoint (RHS), the Remote Low Setpoint
(RLS), and the Remote T_CRIT Setpoint (RCS) user-
programmable temperature limits. An ALERT output will oc-
cur when the measured temperature is: (1) higher than either
the High Setpoint or the T_CRIT Setpoint, or (2) lower than
the Low Setpoint. The ALERT Mask register allows the user
to prevent the generation of these ALERT outputs.
The temperature hysteresis is set by the value placed in the
Hysteresis Register (TH).
The LM64 may be placed in a low power Standby mode by
setting the Standby bit found in the Configuration Register. In
the Standby mode continuous conversions are stopped. In
Standby mode the user may choose to allow the PWM
output signal to continue, or not, by programming the PWM
Disable in Standby bit in the Configuration Register.
The Local Temperature reading and setpoint data registers
are 8-bits wide. The format of the 11-bit remote temperature
data is a 16-bit left justified word. Two 8-bit registers, high
and low bytes, are provided for each setpoint as well as the
temperature reading. Two Remote Temperature Offset
(RTO) Registers: High Byte and Low Byte (RTOHB and
RTOLB) may be used to correct the temperature readings by
adding or subtracting a fixed value based on a different
non-ideality factor of the thermal diode if different from the
graphics processor thermal diode. See Section 4.1 Thermal
Diode Non-Ideality.
1.1 CONVERSION SEQUENCE
The LM64 takes approximately 31.25 ms to convert the
Local Temperature (LT), Remote Temperature (RT), and to
update all of its registers. The Conversion Rate may be
modified using the Conversion Rate Register. When the
conversion rate is modified a delay is inserted between
conversions,
the
actual
conversion
31.25 ms. Different Conversion Rates will cause the LM64 to
draw different amounts of supply current as shown in Figure
3.
time
remains
at
1.2 THE ALERT OUTPUT
When the ALERT Mask bit in the Configuration register is
written as zero the ALERT interrupts are enabled.
The LM64’s ALERT pin is versatile and can produce three
different methods of use to best serve the system designer:
(1) as a temperature comparator (2) as a temperature-based
interrupt flag, and (3) as part of an SMBus ALERT System.
The three methods of use are further described below. The
ALERT and interrupt methods are different only in how the
user interacts with the LM64.
The remote temperature (RT) reading is associated with a
T_CRIT Setpoint Register, and both local and remote tem-
perature (LT and RT) readings are associated with a HIGH
setpoint register (LHS and RHS). The RT is also associated
with a LOW setpoint register (RLS). At the end of every
temperature
reading
a
digital
whether that reading is above its HIGH or T_CRIT setpoint or
below its LOW setpoint. If so, the corresponding bit in the
ALERT Status Register is set. If the ALERT mask bit is low,
any bit set in the ALERT Status Register, with the exception
of Busy or Open, will cause the ALERT output to be pulled
low. Any temperature conversion that is out of the limits
defined in the temperature setpoint registers will trigger an
ALERT. Additionally, the ALERT Mask Bit must be cleared to
trigger an ALERT in all modes.
The three different ALERT modes will be discussed in the
following sections.
comparison
determines
1.2.1 ALERT Output as a Temperature Comparator
When the LM64 is used in a system in which does not
require temperature-based interrupts, the ALERT output
could be used as a temperature comparator. In this mode,
once the condition that triggered the ALERT to go low is no
longer present, the ALERT is negated
(Figure 4)
. For ex-
ample, if the ALERT output was activated by the comparison
of LT
>
LHS, when this condition is no longer true, the
ALERT will return HIGH. This mode allows operation without
software intervention, once all registers are configured dur-
ing set-up. In order for the ALERT to be used as a tempera-
ture comparator, the Comparator Mode bit in the Remote
Diode Temperature Filter and Comparator Mode Register
must be asserted. This is not the power-on default state.
20065506
FIGURE 3. Supply Current vs Conversion Rate
L
www.national.com
9
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