LM64 datasheet(9/29 Pages) NSC

9 / 29 page

1.0 Functional Description

The LM64 Remote Diode Temperature Sensor with Inte-

grated Fan Control incorporates a

∆V

BE-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

Ω resistor to V

DD. 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

time

remains

31.25 ms. Different Conversion Rates will cause the LM64 to

draw different amounts of supply current as shown in Figure

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 comparison determines

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.

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

LM64 数据表(PDF) 9 Page - National Semiconductor (TI)

LM64 数据表(HTML) 9 Page - National Semiconductor (TI)

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

数据表下载