ETC LM76

2000年 第 9期 2000年 9月
《姆踏 电孑琵帑件》
-8-…
撼新 特 器 件 应 用
可碥曜 高铕 煮测 温集 戏 电跨 LM76
天津大学精宿仪器与光电子工程学院
丁茹 李刚
彐Ⅱgh
Precision Programmable IC LJM76(Composed of
TempeFature Sensor aⅡ d Γ
rhermaI window{ComparatOr
、
with Twoˉ Wide Interface
Ding Ru
LM%是
摘 要 :高 精 度 、12位 信 号输 出集成 电路
I'i Gang
由数 字 温 度 传 感 器和 双 线 温 度 窗 口比较 器 组 成 的
,
它具 有 功耗 小 、量程 宽、串行 J总 线接 口等优 ,点 。 文 中介 绍 了该 电路 的 工作特性 、引脚功能及 工作原
理 ,最 后给 出了 LM%用 于 API设 计 的典型应 用电路 。
关键词 :数 字 温度传感器 ;窗 口比较 器 ;超 限警报 ;可 编程 ;LM%
分类号 :TP212。
1
n1
文献标识码 :B
文章编号 :1006-⒆ 77(2000)O9-0008-u
接 口 ,采 用 12位 信号输 出 ,其 最大测量范 围超过
概述
1zT℃
LM%是 一个 由数字温度传感器 、I2C串 行 总
线接 口和温度窗 口比较器组 成 的集成 电路 。在 ⒛℃
~1OO℃ 和 一10℃ ~+笱 ℃ 的温度范 围内 ,其 窗 口比
较器 的 串行 总线 接 口的精度 为 ±1℃ 。在 犭℃ 时 ,
LM%CHM的 精度可达 ±0.5℃ 。它 的开漏 中断输
,LM%的 这些特点使得它可广泛用 于温度控
制系统 、个人计算机保护 、电子测试仪器 、办公设备
、
以及生 物医学仪器等方面。
LM%具
有 以下 特点
:
●窗 口比较器可 简化 ACPI的 设计 ,同 时兼容
温度监视与控制
;
出 (INT)在 温度超过可编程窗 口温度时被激活 ,温
●带有 串行总线接 口
度超 限警报输 出 (T-CRIT-A)在 温度超过可编程 的
●有隔离开漏 中断输 出与超限温度关 闭
危 险极 限温度 (超 过此温度 ,会 损坏
LM%)时 有
;
队列 能将 误 报 情 况 减 至最 少 。 LM%在 系统 上 电后
首先处 于 一 种 缺省 阈值状 态 。其传 感 器 的缺省 阈值
THYm=2℃
,下 限温度 飞。
w=10℃ ,上
限温度 THIGH=“ ℃ ,危 险极 限温度 飞 RF=SO℃ 。
为 :迟 滞 温度
LM%采
引脚号
N
强
LM%的
2
G№
I1`了1Γ
7,6
引脚功能及主要参数
引脚排列 如 图 1所 示 ,各 管脚 的功 能
如表 1所 列 。
LM%的
主要 参数 如下
:
● 电源 电压 :3.3V或 5V;
LM76的 管脚说明
典型连接
功能
串行双 向数据线 ,开 漏输 出 ,CMOS逻 辑 电平
T~cIuT~A
+Vs
AO~A1
2 LM%的
用 3.5V和 5V电 源 ,并 具有 串行 总线
表1
符号
沁
;
LM%的 主机可 以对 窗 口的上 、下限和危
险温度极 限进行编程 ,它 的可编程迟滞特性与故 障
;
●具有最小功耗 的关 闭模式
● 一 条总线可连接 4个 以上 的 LM%芯 片
●采用 12位 信号输 出 ,最 大量程超过 127℃ 。
效。
控制
;
温度超 限警报 ,开 漏输 出
接上拉 电阻 ,控 制器 的
据线
・
接控制器 的 I2C时 钟线`C数
接 上拉 电阻 ,控 制器 的中断线或 系统硬件关 闭端
电源地
接地
中断 ,开 漏输 出
接上拉 电阻 ,控 制器 的中断线
电源 电压正 向输人端
接 3.3V或 5Ⅴ 电源
用 户 设 置 的地 址 输 人 端
接地(低 电平 ,℃
串行 总线 时钟输人 ,③ 泯E逻 辑 电平
”
)或 接 +Vs(高
电平 ,“ 1” )
可编程 高精 度测 温 集成 电路
sDA
+Ⅴ s
sCL
A0
T~CRIT~A
GND
A1
图
电 主3.3Ⅴ 输 出
源 Aux3。 3V
主 3V控 制
3。
-9一
CPU和 所有
主电路电源
控制器
INT
1 LM%的
T~CRIT~A
引脚 排 列
● 电源 电流 :工 作状 态 时为 zs0uA(典 型 ),
笱0uA(最 大 );关 闭状态时为 8uA(最 大 );
●测温精度 :± 0.5℃ (25℃ 时的最大值 );
-10℃ ~+绣 ℃时为 ±1.0℃ (最 大 );
TO℃ ~100℃ 时为 ±1.0℃ (最 大 );
●分辨率 :0。 “zs℃
3 LM%的
LM%
INT输 出
处理机 中断线
图4
LM%作 为从器件在 串行 总线上运行 时 ,SCL
;
内部结构
图 2所 示 为高精 度测温集 成 电路 LM76的 内
部结构框 图 ,可 以看 出 ,LM%温 度传感 器包括 一个
带 隙型温度传感器 、一个 13位 ADC和 一 个可 由用
户设定 上 、下 限值 的数字 比较器 。当温度位 于 TL。w
和 THIGH窗 口外时 ,比 较器激活 INT线 ;当 温度超
过 TcRr时 ,比 较器激活 T-CRIT-A线 。这些 工 作线
对 工 作模式和极 性都是 可编程 的。
与 ACPI规 范相对的温度警报系统
线是输 入线 ,SDA线 是双 向串行数据线 。根据 串行
总线规范 ,LM%有 一 个 7位 受控地 址 ,受 控地址 中
“
的最高有效位设为 10O10” ,另 外两个最低有效位分
配给管脚 A0、 A1,并 通过 A0、 A1接 地或接 +Vs来
“
“
置 0” 或置 1” 。完整 的受控地址为
:
MsB
4
LsB
应用举例
u位
INT
并 且 当温度超过窗 口极 限时 ,LM%会 对微处理器
发 出中断信号 ,其 内部识别标志能迅速判断温度是
信 号 温度 数 字 转换 器
T~CRIT~A
图 3是 一 个满足 ACPI设 计要求 的典型应用 电
路 。其 中 ,LM%可 以对选择 的温度窗 口进行编程
,
上 升 还 是 下 降 。 当温 度 超 过 极 限 温 度 TcRr时
LM%通 过 其 硬 件关 闭 电路 实 现 与微 处 理 器 的断
,
开 。INT输 出与 T-CRIT— A输 出是相 互 分开 的
但可 以通过线一 或连接在 一起 。另外 ,T-CRIT-
,
A0J
亍总线
串彳
接 田和存储器
■
J。
A1。 ■
2 LM%的
结构框 图
咿h.■
图
0.1uF
T~汉 IT~A输 出
A0
地址 A1
硬件关闭
A可 以通过 二极管或 门连接到 INT线 ,这 种方式可
使 T-CRIT-A进 程激活 INT线 ,但 INT进 程不
能激 活 T-CRIT-A线 ,这 在 同时 向微处理器 和
LM76的 T-CRIT-A关 闭 电路报告 的进程 中是
十分有用 的。
图 4所 示为与 ACPI规 范相对应 的温度报警关
闭系统 。该 电路通过 电源 的辅助输 出来启动 LM%,
进而达到关 闭失效或过热 的计算机 ,以 保护尽 可能
多 的系统 。
INT输 出
SDA
接 田 sc1
处理机 中断线
收稿 日期 :2000-03-01
咨询编号 :0OOgO3
图3
典型应用 电路 图
LM76
±0.5°C, ±1°C, 12-Bit + Sign Digital Temperature Sensor and
Thermal Window Comparator with Two-Wire Interface
General Description
Features
The LM76 is a digital temperature sensor and thermal window
comparator with an I2C™ Serial Bus interface with an accuracy of ±1°C. This accuracy for the LM76CHM is specified for
a −10°C to 45°C temperature range. The LM76CHM is specified with an accuracy ±0.5°C at 25°C. The window-comparator architecture of the LM76 eases the design of temperature
control systems conforming to the ACPI (Advanced Configuration and Power Interface) specification for personal computers. The open-drain Interrupt (INT) output becomes active
whenever temperature goes outside a programmable window, while a separate Critical Temperature Alarm
(T_CRIT_A) output becomes active when the temperature
exceeds a programmable critical limit. The INT output can
operate in either a comparator or event mode, while the
T_CRIT_A output operates in comparator mode only.
The host can program both the upper and lower limits of the
window as well as the critical temperature limit. Programmable hysterisis as well as a fault queue are available
to minimize false tripping. Two pins (A0, A1) are available for
address selection. The sensor powers up with default thresholds of 2°C THYST, 10°C TLOW, 64°C THIGH, and 80°C T_CRIT.
The LM76's 5.0V supply voltage, Serial Bus interface, 12-bit
+ sign output, and full-scale range of over 127°C make it ideal
for a wide range of applications. These include thermal management and protection applications in personal computers,
electronic test equipment, office electronics and bio-medical
applications.
■ Window comparison simplifies design of ACPI compatible
temperature monitoring and control.
■ Serial Bus interface
■ Separate open-drain outputs for Interrupt and Critical
Temperature shutdown
■ Shutdown mode to minimize power consumption
■ Up to 4 LM76s can be connected to a single bus
■ 12-bit + sign output; full-scale reading of over 127°C
Key Specifications
■ Supply Voltage
■ Supply Current
5.0V
operating
250 μA (typ)
450 μA (max)
+25°C
8 μA (max)
±0.5°C(max)
−10°C to +45°C
70°C to 100°C
±1.0°C(max)
±1.0°C(max)
shutdown
■ Temperature
Accuracy
■ Resolution
0.0625°C
Applications
■
■
■
■
System Thermal Management
Personal Computers
Office Electronics
HVAC
I2C® is a registered trademark of Philips Corporation.
© 2010 National Semiconductor Corporation
101015
www.national.com
LM76 ±0.5°C, ±1°C, 12-Bit + Sign Digital Temperature Sensor and Thermal Window Comparator
with Two-Wire Interface
November 2, 2010
LM76
Simplified Block Diagram
10101501
Connection Diagram
SO-8
10101502
LM76 See NS Package Number M08A
Ordering Information
Supply Voltage
Acurracy
Temperature
Range for
Accuracy
LM76CHM-5
5.0V
±0.5°C
±1.0°C
25°C
−10°C to 45°C
95 units in Rail
LM76CHMX-5
5.0V
±0.5°C
±1.0°C
25°C
−10°C to 45°C
2500 Units on Tape and Reel
Order Number
www.national.com
2
Transport Media
LM76
Pin Descriptions
Label
Pin #
Function
Typical Connection
SDA
1
Serial Bi-Directional Data Line, Open Drain Output, CMOS
Pull Up Resistor, Controller I2C Data Line
Logic Level
SCL
2
Serial Bus Clock Input, CMOS Logic Level
From Controller I2C Clock Line
T_CRIT_A
3
Critical Temperature Alarm, Open Drain Output
Pull Up Resistor, Controller Interrupt Line or
System Hardware Shutdown
GND
4
Power Supply Ground
Ground
INT
5
Interrupt, Open Drain Output
Pull Up Resistor, Controller Interrupt Line
User-Set Address Inputs, TTL Logic Level
Ground (Low, “0”) or +VS (High, “1”)
Positive Supply Voltage Input
DC Voltage from 3.3V power supply or 5V.
A0–A1
+VS
7, 6
8
10101503
FIGURE 1. Typical Application
3
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LM76
Absolute Maximum Ratings (Note 1)
Supply Voltage
Voltage at any Pin
Input Current at any Pin
Package Input Current (Note 2)
T_CRIT_A and
INT Output Sink Current
T_CRIT_A and
INT Output Voltage
Storage Temperature
Soldering Information, Lead
Temperature
SOP Package (Note 3)
Vapor Phase (60 seconds)
Infrared (15 seconds)
ESD Susceptibility (Note 4)
Human Body Model
Machine Model
Operating Ratings
(Note 1, Note 5)
Operating Temperature Range
Specified Temperature Range
(Note 6)
LM76CHM-5
Supply Voltage Range (+VS)(Note 7)
−0.3V to 6.5V
−0.3V to (+VS + 0.3V)
5mA
20mA
−55°C to +150°C
TMIN to TMAX
−20°C to +85°C
+4.5V to +5.5V
10mA
6.5V
−65°C to +125°C
215°C
220°C
3000V
250V
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for +VS = +5.0 Vdc ±10% for the LM76CHM-5. (Note 7). Boldface limits apply
for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25°C, unless otherwise noted.
Parameter
Typical
(Note 8)
Conditions
TA = +70°C to +100°C
Accuracy (Note 7)
LM76CHM-5
Limits
(Note 9)
Units
(Limit)
±1.0
TA = −20°C to +85°C for
LM76CHM-5
±1.5
TA = −10°C to +45°C
±1.0
TA = +25°C
±0.5
13
0.0625
Resolution
(Note 10)
Temperature Conversion Time
(Note 11)
400
I2C Inactive
0.25
I2C Active
0.25
Quiescent Current
LM76CNM-3
Limits
(Note 9)
Shutdown Mode:
Bits
°C
500
1000
0.5
0.45
5
18
8
TA = +25°C
mA (max)
µA
12
TA = +85°C
ms
mA
µA (max)
µA (max)
12
µA (max)
THYST Default Temperature
(Note 13, Note 14)
2
°C
TLOW Default Temperature
(Note 14)
10
°C
THIGH Default Temperature
(Note 14)
64
°C
TCRIT Default Temperature
(Note 14)
80
°C
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4
LM76
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for +VS = +5.0 Vdc ±10% for the
LM76CHM-5. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25°C, unless otherwise noted.
Symbol
Parameter
VIN(1)
SDA and SCL Logical “1” Input
Voltage
VIN(0)
SDA and SCL Logical “0” Input
Voltage
VIN(HYST)
SDA and SCL Digital Input Hysteresis
VIN(1)
Conditions
Typical
(Note 8)
500
A0 and A1 Logical “1” Input Voltage
Limits
(Note 9)
Units
(Limit)
+VS × 0.7
V (min)
+VS+0.3
V (max)
−0.3
V (min)
+VS × 0.3
V (max)
250
mV (min)
2.0
V (min)
+VS+0.3
V (max)
−0.3
V (min)
0.8
V (max)
VIN(0)
A0 and A1 Logical “0” Input Voltage
IIN(1)
Logical “1” Input Current
VIN = + VS
0.005
1.0
μA (max)
IIN(0)
Logical “0” Input Current
VIN = 0V
−0.005
−1.0
μA (max)
CIN
Capacitance of All Digital Inputs
IOH
High Level Output Current
VOH = + VS
10
μA (max)
VOL
Low Level Output Voltage
IOL = 3 mA
0.4
V (max)
0.8
V (max)
1
Conversions
(max)
250
ns (max)
20
I
= 4.0 mA
T_CRIT_A Output Saturation Voltage OUT
(Note 12)
pF
T_CRIT_A Delay
tOF
CL = 400 pF
Output Fall Time
IO = 3 mA
SERIAL BUS DIGITAL SWITCHING CHARACTERISTICS Unless otherwise noted, these specifications apply for +VS = +5.0 Vdc
±10% for the LM76CHM-5, CL (load capacitance) on output lines = 80 pF unless otherwise specified. Boldface limits apply for
TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25°C, unless otherwise noted.
Symbol
Parameter
Conditions
Typical
(Note 8)
Limits
(Note 9,
Note 15)
Units
(Limit)
t1
SCL (Clock) Period
2.5
μs(min)
t2
Data in Set-Up Time to SCL High
100
ns(min)
t3
Data Out Stable after SCL Low
0
ns(min)
t4
SDA Low Set-Up Time to SCL Low (Start Condition)
100
ns(min)
t5
SDA High Hold Time after SCL High (Stop Condition)
100
ns(min)
10101504
5
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LM76
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating
the device beyond its rated operating conditions.
Note 2: When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > +VS) the current at that pin should be limited to 5 mA. The 20 mA
maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four.
Note 3: See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” or the section titled “Surface Mount” found in a current National
Semiconductor Linear Data Book for other methods of soldering surface mount devices.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine model, 200 pF discharged directly into each pin.
Note 5: LM76 θJA (thermal resistance, junction-to-ambient) when attached to a printed circuit board with 2 oz. foil is 200°C/W.
Note 6: While the LM76 has a full-scale-range in excess of 128°C, prolonged operation at temperatures above 125°C is not recommended.
Note 7: The LM76 will operate properly over the +VS supply voltage range of 3V to 5.5V for the LM76CNM-3 and the LM76CHM-5. The LM76CNM-3 is tested
and specified for rated accuracy at the nominal supply voltage of 3.3V. Accuracy of the LM76CNM-3 will degrade 0.2°C for a ±1% variation in +VS from the nominal
value. The LM76CHM-5 is tested and specified for a rated accuracy at the nominal supply voltage of 5.0V. Accuracy of the LM76CHM-5 will degrade 0.08°C for
a ±1% variation in +VS from the nominal value.
Note 8: Typicals are at TA = 25°C and represent most likely parametric norm.
Note 9: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 10: 12 bits + sign, two's complement
Note 11: This specification is provided only to indicate how often temperature data is updated. The LM76 can be read at any time without regard to conversion
state (and will yield last conversion result). If a conversion is in process it will be interrupted and restarted after the end of the read.
Note 12: For best accuracy, minimize output loading. Higher sink currents can affect sensor accuracy with internal heating. This can cause an error of 0.64°C at
full rated sink current and saturation voltage based on junction-to-ambient thermal resistance.
Note 13: Hysteresis value adds to the TLOW setpoint value (e.g.: if TLOW setpoint = 10°C, and hysteresis = 2°C, then actual hysteresis point is 10+2 = 12°C); and
subtracts from the THIGH and T_CRIT setpoints (e.g.: if THIGH setpoint = 64°C, and hysteresis = 2°C, then actual hysteresis point is 64−2 = 62°C). For a detailed
discussion of the function of hysteresis refer to Section 1.1, TEMPERATURE COMPARISON, and Figure 3.
Note 14: Default values set at power up.
Note 15: Timing specifications are tested at the bus input logic levels (Vin(0)=0.3xVA for a falling edge and Vin(1)=0.7xVA for a rising edge) when the SCL and
SDA edge rates are similar.
10101505
FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
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6
The LM76 temperature sensor incorporates a band-gap type
temperature sensor, 13-bit ADC, and a digital comparator
with user-programmable upper and lower limit values. The
comparator activates either the INT line for temperatures outside the TLOW and THIGH window, or the T_CRIT_A line for
temperatures which exceed T_CRIT. The lines are programmable for mode and polarity.
1.1 TEMPERATURE COMPARISON
LM76 provides a window comparison against a lower (TLOW)
and upper (THIGH) trip point. A second upper trip point
(T_CRIT) functions as a critical alarm shutdown. Figure 3 depicts the comparison function as well as the modes of operation.
1.2 DEFAULT SETTINGS
The LM76 always powers up in a known state. LM76 power
up default conditions are:
1.1.1 Status Bits
The internal Status bits operate as follows:
“True”: Temperature above a THIGH or T_CRIT is “true” for
those respective bits. A “true” for TLOW is temperature below
TLOW.
“ False”: Assuming temperature has previously crossed
above THIGH or T_CRIT, then the temperature must drop below the points corresponding THYST(THIGH − THYST or
T_CRIT − THYST) in order for the condition to be false. For
TLOW, assuming temperature has previously crossed below
TLOW, a “false” occurs when temperature goes above TLOW +
THYST.
The Status bits are not affected by reads or any other actions,
and always represent the state of temperature vs. setpoints.
1. Comparator Interrupt Mode
2. TLOW set to 10°C
3. THIGH set to 64°C
4. T_CRIT set to 80°C
5. THYST set to 2°C
6. INT and T_CRIT_A active low
7. Pointer set to “00”; Temperature Register
The LM76 registers will always reset to these default values
when the power supply voltage is brought up from zero volts
as the supply crosses the voltage level plotted in the following
curve. The LM76 registers will reset again when the power
supply drops below the voltage plotted in this curve.
Average Power on Reset Voltage
vs Temperature
1.1.2 Hardwire Outputs
The T_CRIT_A hardwire output mirrors the T_CRIT_A flag,
when the flag is true, the T_CRIT_A output is asserted at all
times regardless of mode. Reading the LM76 has no effect
on the T_CRIT_A output, although the internal conversion is
restarted.
The behavior of the INT hardwire output is as follows:
Comparator Interrupt Mode (Default): User reading part
resets output until next measurement completes. If condition
is still true, output is set again at end of next conversion cycle.
For example, if a user never reads the part, and temperature
goes below TLOW then INT becomes active. It would stay that
way until temperature goes above TLOW + THYST. However if
the user reads the part, the output would be reset. At the end
of the next conversion cycle, if the condition is true, it is set
again. If not, it remains reset.
Event Interrupt Mode: User reading part resets output until
next condition "event" occurs (in other words, output is only
set once for a true condition, if reset by a read, it remains reset
until the next triggering threshold has been crossed). Conversely, if a user never read the part, the output would stay
set indefinitely after the first event that set the output. An
“event” for Event Interrupt Mode is defined as:
10101518
1.3 SERIAL BUS INTERFACE
The LM76 operates as a slave on the Serial Bus, so the SCL
line is an input (no clock is generated by the LM76) and the
SDA line is a bi-directional serial data line. According to Serial
Bus specifications, the LM76 has a 7-bit slave address. The
five most significant bits of the slave address are hard wired
inside the LM76 and are “10010”. The two least significant bits
of the address are assigned to pins A1–A0, and are set by
connecting these pins to ground for a low, (0); or to +VS for a
high, (1).
Therefore, the complete slave address is:
1.
2.
Transitioning upward across a setpoint, or
Transitioning downward across a setpoint's
corresponding hysteresis (after having exceeded that
setpoint).
For example, if a user never read the part, and temperature
went below TLOW then INT would become active. It would stay
that way forever if a user never read the part.
However if the user read the part, the output would be reset.
Even if the condition is true, it will remain reset. The temperature must cross above TLOW + THYST to set the output again.
1
MSB
7
0
0
1
0
A1
A0
LSB
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LM76
In either mode, reading any register in the LM76 restarts the
conversion. This allows a designer to know exactly when the
LM76 begins a comparison. This prevents unnecessary Interrupts just after reprogramming setpoints. Typically, system
Interrupt inputs are masked prior to reprogramming trip
points. By doing a read just after resetting trip points, but prior
to unmasking, unexpected Interrupts are prevented.
Avoid programming setpoints so close that their hysteresis
values overlap. An example would be that with a THYST value
of 2°C then setting THIGH and TLOW to within 4°C of each other
will violate this restriction. To be more specific, with THYST set
to 2°C assume THIGH set to 64°C. If TLOW is set equal to, or
higher than 60°C this restriction is violated.
1.0 Functional Description
LM76
10101506
Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn't read, the outputs would go low and stay that way until the LM76 is read.
FIGURE 3. Temperature Response Diagram
1.4 TEMPERATURE DATA FORMAT
Temperature data can be read from the Temperature and Set
Point registers; and written to the Set Point registers. Temperature data can be read at any time, although reading faster
than the conversion time of the LM76 will prevent data from
being updated. Temperature data is represented by a 13-bit,
two's complement word with an LSB (Least Significant Bit)
equal to 0.0625°C:
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Temperature
Digital Output
Binary
8
Hex
+130°C
0 1000 0 010 0000
08 20h
+125°C
0 0111 1101 0000
07 D0h
+80°C
0 0101 1010 0000
05 90h
+64°C
0 0100 0000 0000
04 00h
+25°C
0 0001 1001 0000
01 90h
+10°C
0 0000 1010 0000
00 A0h
+2°C
0 0000 0010 0000
00 20h
+0.0625°C
0 0000 0000 0001
00 01h
0°C
00 0000 0000
00 00h
−0.0625°C
1 1111 1111 1111
1F FFh
−25°C
1 1110 0111 0000
1E 70h
−55°C
1 1100 1001 0000
1C 90h
1.7 FAULT QUEUE
A fault queue of up to 4 faults is provided to prevent false
tripping when the LM76 is used in noisy environments. The 4
faults must occur consecutively to set flags as well as INT and
T_CRIT_A outputs. The fault queue is enabled by setting bit
4 of the Configuration Register high (see Section 1.11).
1.6 INT AND T_CRIT_A OUTPUT
The INT and T_CRIT_A outputs are open-drain outputs and
do not have internal pull-ups. A "high" level will not be ob1.8 INTERNAL REGISTER STRUCTURE
10101507
There are four data registers in the LM76, selected by the
Pointer register. At power-up the Pointer is set to “00”; the
location for the Temperature Register. The Pointer register
latches the last location it was set to. In Interrupt Mode, a read
from the LM76 resets the INT output. Placing the device in
Shutdown mode resets the INT and T_CRIT_A outputs. All
registers are read and write, except the Temperature register
which is read only.
A write to the LM76 will always include the address byte and
the Pointer byte. A write to the Configuration register requires
one data byte, while the TLOW, THIGH, and T_CRIT registers
require two data bytes.
Reading the LM76 can take place either of two ways: If the
location latched in the Pointer is correct (most of the time it is
expected that the Pointer will point to the Temperature register because it will be the data most frequently read from the
LM76), then the read can simply consist of an address byte,
followed by retrieving the corresponding number of data
bytes. If the Pointer needs to be set, then an address byte,
pointer byte, repeat start, and another address byte plus required number of data bytes will accomplish a read.
The first data byte is the most significant byte with most significant bit first, permitting only as much data as necessary to
be read to determine the temperature condition. For instance,
if the first four bits of the temperature data indicates a critical
condition, the host processor could immediately take action
to remedy the excessive temperature. At the end of a read,
the LM76 can accept either Acknowledge or No Acknowledge
from the Master (No Acknowledge is typically used as a signal
for the slave that the Master has read its last byte).
An inadvertent 8-bit read from a 16-bit register, with the D7
bit low, can cause the LM76 to stop in a state where the SDA
line is held low as shown in Figure 4. This can prevent any
further bus communication until at least 9 additional clock cy-
9
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LM76
served on these pins until pull-up current is provided from
some external source, typically a pull-up resistor. Choice of
resistor value depends on many system factors but, in general, the pull-up resistor should be as large as possible. This
will minimize any errors due to internal heating of the LM76.
The maximum resistance of the pull up, based on LM76 specification for High Level Output Current, to provide a 2 volt high
level, is 30K ohms.
1.5 SHUTDOWN MODE
Shutdown mode is enabled by setting the shutdown bit in the
Configuration register via the Serial Bus. Shutdown mode reduces power supply current to 5 μA typical. T_CRIT_A is reset
if previously set. Since conversions are stoped during shutdown, T_CRIT_A and INT will not be operational. The Serial
Bus interface remains active. Activity on the clock and data
lines of the Serial Bus may slightly increase shutdown mode
quiescent current. Registers can be read from and written to
in shutdown mode. The LM76 takes miliseconds to respond
to the shutdown command.
LM76
cles have occurred. Alternatively, the master can issue clock
cycles until SDA goes high, at which time issuing a “Stop”
condition will reset the LM76.
10101508
FIGURE 4. Inadvertent 8-Bit Read from 16-Bit Register where D7 is Zero (“0”)
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10
LM76
1.9 POINTER REGISTER
(Selects which registers will be read from or written to):
P7
P6
P5
P4
P3
0
0
0
0
0
P2
P1
P0
Register Select
P0–P2: Register Select:
P2
P1
P0
0
0
0
Temperature (Read only) (Power-up default)-
Register
0
0
1
Configuration (Read/Write)
0
1
0
THYST (Read/Write)
0
1
1
T_CRIT (Read/Write)
1
0
0
TLOW (Read/Write)
1
0
1
THIGH (Read/Write)
P3–P7: Must be kept zero.
1.10 TEMPERATURE REGISTER
(Read Only):
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
Sign
MSB
Bit 10
Bit 9
Bit 8
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
CRIT
D1
D0
HIGH
LOW
Status Bits
D0–D2: Status Bits
D3–D15: Temperature Data. One LSB = 0.0625°C. Two's complement format.
1.11 CONFIGURATION REGISTER
(Read/Write):
D7
D6
0
D5
0
D4
0
Fault Queue
D3
D2
D1
D0
INT Polarity
T_CRIT_A
Polarity
INT Mode
Shutdown
D0: Shutdown - When set to 1 the LM76 goes to low power shutdown mode. Power up default of “0”.
D1: Interrupt mode - 0 is Comparator Interrupt mode, 1 is Event Interrupt mode. Power up default of “0”.
D2, D3: T_CRIT_A and INT Polarity - 0 is active low, 1 is active high. Outputs are open-drain. Power up default of “0”
D4: Fault Queue - When set to 1 the Fault Queu is enabled, see Section 1.7. Power up default of “0”.
D5–D7: These bits are used for production testing and must be kept zero for normal operation.
1.12 THYST, TLOW, THIGH AND T_CRIT_A REGISTERS
(Read/Write):
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
Sign
MSB
Bit 10
Bit 9
Bit 8
Bit7
Bit6
Bit5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
X
X
X
D0–D2: Undefined
D3–D15: THYST, TLOW, THIGH or T_CRIT Trip Temperature Data. Power up default is TLOW = 10°C, THIGH = 64°C, T_CRIT = 80°C,
THYST = 2°C.
THYST is subtracted from THIGH, and T_CRIT, and added to TLOW.
Avoid programming setpoints so close that their hysteresis values overlap. See Section 1.1.
11
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LM76
2.0 I2C Timing Diagrams
10101509
Typical 2-Byte Read From Preset Pointer Location Such as Temp or Comparison Registers
10101510
Typical Pointer Set Followed by Immediate Read for 2-Byte Register such as Temp or Comparison Registers
10101511
Typical 1-Byte Read from Configuration Register with Preset Pointer
FIGURE 5. Timing Diagrams
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12
LM76
10101512
Typical Pointer Set Followed by Immediate Read from Configuration Register
10101513
Configuration Register Write
10101514
Comparison Register Write
FIGURE 6. Timing Diagrams
13
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LM76
issue an interrupt, service the interrupt, and reprogram the
window according to the desired granularity of the temperature scale. The reprogrammed window will now have the
current temperature inside it, ready to issue an interrupt
whenever the temperature deviates from the current window.
To understand this graph, assume that at the left hand side
the system is at some nominal temperature. For the 1st event
temperature rises above the upper window limit, THIGH, causing INT to go active. The system responds to the interrupt by
querying the LM76's status bits and determines that THIGH
was exceeded, indicating that temperature is rising. The system then reprograms the temperature limits to a value higher
by an amount equal to the desired granularity. Note that in
Event Interrupt Mode, reprogramming the limits has caused
a second, known, interrupt to be issued since temperature
has been returned within the window. In Comparator Interrupt
Mode, the LM76 simply stops issuing interrupts.
The 2nd event is another identical rise in temperature. The
3rd event is typical of a drop in temperature. This is one of the
conditions that demonstrates the power of the LM76, as the
user receives notification that a lower limit is exceeded in such
a way that temperature is dropping.
The Critical Alarm Event activates the separate T_CRIT_A
output. Typically, this would feed circuitry separate from the
processor on the assumption that if the system reached this
temperature, the processor might not be responding.
3.0 Application Hints
The temperature response graph in Figure 7 depicts a typical
application designed to meet ACPI requirements. In this type
of application, the temperature scale is given an arbitrary value of "granularity", or the window within which temperature
notification events should occur. The LM76 can be programmed to the window size chosen by the designer, and will
issue interrupts to the processor whenever the window limits
have been crossed. The internal flags permit quick determination of whether the temperature is rising or falling.
The T_CRIT limit would typically use its separate output to
activate hardware shutdown circuitry separate from the processor. This is done because it is expected that if temperature
has gotten this high that the processor may not be responding. The separate circuitry can then shut down the system,
usually by shutting down the power supply.
Note that the INT and T_CRIT_A outputs are separate, but
can be wire-or'd together. Alternatively the T_CRIT_A can be
diode or'd to the INT line in such a way that a T_CRIT_A event
activates the INT line, but an INT event does not activate the
T_CRIT_A line. This may be useful in the event that it is desirable to notify both the processor and separate T_CRIT_A
shutdown circuitry of a critical temperature alarm at the same
time (maybe the processor is still working and can coordinate
a graceful shutdown with the separate shutdown circuit).
To implement ACPI compatible sensing it is necessary to
sense whenever the temperature goes outside the window,
10101515
Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn't read, the outputs would go low and stay that way until the LM76 is read.
FIGURE 7. Temperature Response Diagram for ACPI Implementation
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14
LM76
4.0 Typical Applications
10101516
FIGURE 8. Typical Application
10101519
FIGURE 9. ACPI Compatible Terminal Alarm Shutdown. By powering the LM76 from auxiliary output of the power supply,
a non-functioning overheated computer can be powered down to preserve as much of the system as possible.
15
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LM76
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead (0.150″ Wide) Molded Small Outline Package (SOP), JEDEC
Order Number LM76CNM-3, LM76CNMX-3, LM76CHM-5 or LM76CHM-5X
NS Package Number M08A
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16
LM76 ±0.5°C, ±1°C, 12-Bit + Sign Digital Temperature Sensor and Thermal Window Comparator
with Two-Wire Interface
Notes
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