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电源散热风扇控制器 FsCT× ×A-UH5
原理及应用
化清
艹
景 海
栾 武
山东沂光电子股份有 限公 司
山东永光电子有 限公 司
,
无 服
要 :sT公 司生产的 FsCT× ×A UH5无 刷 DC风 扇速度控制器 IC,仅 需一个或两个外部元件
NTC热 敏 电阻,可 根据温度线性控制和调 节风扇速度 .这 种低成本控制器,主 要用于计算机 、
务器和通信 电源的通风散热
关键词 :FsCT× ×Aˉ UH5;风 扇控制器;低 成本;低 噪音
摘
需外部
.
(sT)公 司最近推 出 FsCT系 列无
刷 DC风 扇 电机 控 制 器 芯 片 ,是 专 门为 用 于 台式
PC、 笔记本 PC和 服 务器 电源 及其 它各种需要通 风
意法半 导体
的消 费类 设备而专 门 设计 的 。FsCT系 列风扇速 度
控 制 器 IC含 有 二 个 型 号 ,即 FsCTo7A UH5、
FsCTl1A UH5和 FsCT17A UH5,每 种 器 仵 输 出 电
压 随温 度变 化 的斜 率及 最 大 【
t扇 速 度 卜的最 低温
。
度是不 同的
1FsCT的 封装、内部结构及引脚功能
FsCT× ×Aˉ UH5(以 下简称 FsCT)采 用 5引
脚 塑料 IP队 Κ 封 装 ,重 04g,夕 卜
形如 图 1(a)所
'六
。
电路 、滞 后 比较器 、接通 调节器 、驱动器及 NPN
晶体管输 出级等 ,其 内部结构 与外部 电路如图 1(b)
所示 。
FsCT的 引脚功能如表 1所 列 。
表 1引 脚功能
引脚
名称
1
TEsT
2
Vcc
3
CND
4
oN
5
oUT
功能说 明
测试 脚 ,该 脚必须 不被连接
工 作 DC电 压 ,范 围为 9~15V
地 ,在 内部连接到芯片散热 片 Tab
模式接通 和大断选 择 端
输 出端 ,外 部连接
PNP晶 体管 的基极
2电 气特性 及 主要 特 点
21主 要参数
FsCT主 要参数及其指标如下
◆
电源 电压 Vcc:9~15Vac;
:
◆
◆
工 作 电流 Icc:11mA(典 型值 );
输 出灌 电流 I。 L(外 部 PNP管 基 极 电流 ):
≥ 10mA;
接 通 模式输 出最低 电压 V。 L:055V(最 大
值是 07V);
◆
接通模 式风扇最低速度输 出电压 V。 Ms:
53V(最 人值是 55V);
◆
温度调节 门限电平 TMs:32℃ (典 型值 );
◆
关断模式接通温度 %N:71℃ (典 型值 );
◆
关断温度 T。 FF:39℃ (典 型值 );
◆ 工 作结温 Tj:0℃ ~125℃ 。
三 种 IC的 输 出温度斜率 KsL、 风扇最大速 度最
◆
(b)内 部 结 构及 外部 元 件连接
图 1 FsCT× ×A UH5的 外形封装 、内部 结 构
和外部连接
FSCT内 置温 度传感器 、参考 电压 、开/关 选择
'
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2000年 第 8期
(总 第 45期 )《 中ΘV彳 博 览》
臼
o`
●●
助 c无 mo∶og
低温度 T。 L和 在 V。 LlT=3V下 的 Tab温 度
差另刂, 女口表 2所 歹刂。
Ksd mW℃
)
T° L(℃ )
FsCT11A-UH5
:
η
(2)
)
`3(℃
'°
FsCT17A-UH5
81
107
'°
FsCTO7A-UH5
FsCT具 有 以下几方面 的特 点
(1)芯 片集成 了温度传感器 ,输 出模拟 电压
(Ⅴ 。
vT)与 %b温 度成 正 比 ,线 性控制外部与无刷
风扇 电机 串联在 一 起 的 PNP晶 体管 ,从 而控制风扇
:
;
(2)外 部 晶体管 的线性控制减小 了声学噪音
在绿色模式操 作期间 ,由 于大 的滞后特性有效 抑制
,
了开/关 振荡
由于 PNP晶 体 管 作 为线 性 放 大器 工 作 ,与
PWM控 制 电路 比较 ,有 较小的 EMI和 声学噪声b
当 FSCT的 脚 0N悬 空或在该脚施加 一 个逻辑
高 电平 电压 时 ,接 通模式被激活 。在该模式下 ,输
出电压 V∞ T根 据结温 (TJ)出 现 三种特性
(a〉 着 Tl<TMs,为 防 止风扇 电机 失速 ,Vc,LlT被
:
22主 要特点
速度
接 AppⅡc油 Ⅱ
管 ,一 个 10111A的 基极 电流 ,其 发射 结正 向压 降
Ⅴ:E约 lV。 若风扇 电源 电压 VFsN+=12V,那 么施加
到风扇 上的 电压则为
V弘 M=VFANfV:E VouT=12V1V-V。 uT〓 11VV° uT
TV3存 在
表 2三 种 IC参 数 比较
型号
R引 ecrc尼
:
oN脚 (4脚 )输 出逻辑高 电平 (≥ 1V),
或者 oN脚 悬 空 ,选 择接通模式 ;若 在 0N脚 输 入
一 个逻辑低 电平 (≤ 03V),则 选择关断模式
(3)在
限制
;
(b)若
TMs<TJ(ToL,Vclt T随 结温被线性调节
;
(c)若 TJ)T° Lγ c,tlT被 钳位于其最小值 Vc,L(典
型值是 055Ⅴ ,最 大不超 过 07V)上 。
当在 0N脚 施加 一 个逻辑低 电平 电压 时 ,FsCT
进 入 关断模式 。在该模式 下 ,一 旦温 度超过 T。 N值
一 个滞后控制允 许系统转换到导通模式 。当系统冷
却到 T。 FF温 度 以下时 ,风 扇 则重新关断 。图 2示 出
了两种 工 作模式不 同温度 下的输 出特性 。
,
;
(4)高 集成度 可只需用 一 个 (PNP晶 体管 )
或两个 (一 只 100nF的 电容和 一 只 PNP晶 体管 )元
件
;
(5)输 出驱动 电流不低 于 10IllA,可 控制 12V,
200nlA的 DC风 扇 电机 。
3工 作 原 理
FsCT芯 片 上 的温度传感 器 ,直 接 由硅 特性产
生 。它是 一 个正 比于绝对温度 的精密 电压参考 ,其
・
硅热 电压 Vt为 :Vr=
Kr
1(℃ 〉
(1)
图2
日
公式 中 ,K为 玻尔 兹曼常数 ,T为 绝对温 度 (Κ ),
lQ℃
「
Ⅱ
这种感测方法 ,呈 现 一 个 +2mV/℃ 的正温度系
数 。与晶体管 BE结 电压 V:E传 感方法 (带 圪mw
q〓 16× 1σ
℃温 度系数 ,有 时用于热保护 )比 较 ,有 更高 的精
度 。信 号经过处理 ,可 提供期望的输 出电压范 围 。
众所周知 ,无 刷 DC电 机 的优 点是有 一 个类似
线性 的速度一 电压特性 。因此 ,风 扇速度随施加到
它 上 面 的电压变化而线性变化 。 当 FsCT的 %b感
测 的温度变化时 ,它 的输 出电压 V。 F也 随之改变
并 且 V∞ T随 温度升高而减小 ,施 加到风扇 电机上
的电压则随温度升高而增大 。对于外部 PNP晶 体
,
t「
VOUT与
Tj关 系曲线
当温度低 于 TMs(37℃
)时 ,V。 uT被 钳位在
V。 Ms电 平 上 。由于 V。 Ms最 大值是
55V,根 据公式
(2)可 知 ,风 扇 上 的电压为 55V。 该 电压在大多
数风扇 电机 的失速 电压之 上 ,从 而保证在接通模式
风扇总是运转 ,避 免 了在低温下 因电压太低而 出现
虚假关断 。
当 FsCT脚 oN上 的信号为低 电平 时 ,输 出电
(Vc,LlT)为
压
高 电平 ,风 扇 因电机 上 电压过低而停
止运转 。
在 关 断模 式 ,风 扇 能够 节 约 能量 消耗 。对 于
12V、 ⒛ 0mA的 DC电 机 ,风 扇关 闭能节省 05~
25W的 功率 。在模式关断期间 ,FsCT不 能丢 失温
/
囤
⒛ OzI年 第
8期
(总 第 zIs期 )《 十Θ 唿 俦傅 览》
o山
￠
Po”e`sIJPP,s口
r,,锣
TBc△ moJog/R贺 cJrch设 AppI记a劫刀
度控制 。事实上 ,在 温度过高时 ,风 扇 自动接通 。
当温度低 于 %FF时 ,为 保持节 能优 点 ,风 扇返 回到
关断模式 。
在关断模式 FsCT的 温度变化 情况如 图 3所 示 。
曲线示 出的三 种情况如下
:
`●
:∶
通 状态 ,如 曲线③ 。
例如 ,FsCT17A UH5用 于 一 个 200W的 计算
机 电源 中 (FsCT17A uH5放 置 到半导体功率器件
散热器上 ),对 于 一 个 乃w的 功率消耗 ,第 一 种情
况可 以达到 。在此情况下 ,TJ稳 定在 ω ℃左 右 ,总
是低于 T。 N(71℃ )。 第 二 种情况可 以达 到 50W的
功率消耗 ,由 于 一 个大 的滞 后值 (30℃ ),开 /关 周
期 (Tp)至 少为 15分 钟 ,大 大减小 了每小时风扇
启动 次数 。第 三 种情况能达到不低 于 75W的 功率
消耗 ,电 源环境温度稳定 在 42℃ 左右 。
4安 装 考 虑
图 3 温度 变化 情 况
FsCT的 %b直 接连接到接地脚 (GND脚 ),
当 FsCT被 粘 结到散热器 上 时 ,如 果该散热器与
FsCT的 Tab是 在不 同的电压上 ,在 Tab与 散热器
之 问必须加进 电隔离垫片 。为减小热 阻 ,宜 使用夹
片将 1PPAK壳 体与散热器紧紧压在 一起 ,如 图 4
所示 。
5结 束 语
FsCT× ×A-UH5是 一种低成本 电源散热风 扇
U形 夹片将 FsCT与 散 热器 夹牢
(1)当 加热功率太低 时 ,TJ<ToN,风 扇停 留
在关断状态 ,如 (图 3)曲 线①
(2)加 热功率高于第 一 种情况 ,TJ可 升至 T。 N
以上 ,但 因该功率仍然较低 ,Tl叉 降至 T。 FF。 当温
度再次升高到 T。 N时 ,风 扇又开始运转 ,于 是形成
开/关 周期 (Tp),如 曲线②
(3)加 热功率高于第 二 种情况 ,TJ总 是高于
图 4用
;
速度控制器 ,在 应 用 中仅 需外加 一 两个元件 ,无 需
使用 NTC热 敏 电阻 ,并 消除 了开/关 振荡和噪声 。
FsCT内 置温 度传感器 ,根 据温度来执行风扇速 度
的线性控制 与调节 。无刷 DC风 扇 电机 串接在 由
FsCT驱 动 的 PNp晶 体管的发射极 (集 电极接地 ),
FsCT的 输 出电压与其 %b的 温度成正 比,用 作线
性控制 PNP晶 体管 ,施 加到 电机上 的 电压相应变
化 ,从 而 使风 扇速 度 改变 (其 中包括 风扇 停 止运
转 )。 ◆
,风 扇在加热功率不减 小的情况下 ,停 留在接
T。 可
2004年 第 8期
(总 第 45期 )《 中0呻 诤博 览》
FSCTxxA-UH5
®
A.S.D.TM
Application Specific Discretes
FAN SPEED CONTROLER
APPLICATIONS
COMPUTER AND SERVER POWER SUPPLY
TELECOM
LOW COST VENTILATION
■
■
■
FEATURES
Built in thermal sensor
Brushless DC fan speed control
Linear control and regulation of the fan speed
according to the temperature
Green OFF mode operation with automatic
turn- ON in case of overtemperature
Voltage limitation above fan stall voltage
Built in linear temperature sensor
5
■
1
■
IPPAK
■
■
Fig. 1: Block Diagram.
■
■
ON
BENEFITS
Low cost integrated fan speed control
High integration: only one or two external components
Reduced acoustic noise because of the linear
control of the external transistor
Power supply noise rejection
Good thermal coupling with heater
Reduced ON/OFF oscillation because of large
hysteresis
High current capability (base current higher
than 10 mA)
Higher accuracy than discrete circuit with NTC
BIAS
FSCTxxA-UH5
■
■
F
VCC
ON/OFF
HIGH
ON/OFF
LOW
VOLTAGE
REF.
ON
REGULATION
HYSTERESIS
COMPARATOR
OUT
■
■
HYST.-EN
TEMP.
SENSOR
COUT=
100nF
VT
DRIVER
■
■
GND
■
■
GENERAL DESCRIPTION
The FSCTxxA-UH5 is a high-integrated low cost fan speed controller suitable for PC desktops, notebooks
and server power supplies and also all kind of equipments where low cost ventilation system is needed. An
internal thermal sensor connected to the tab is used to regulate the fan speed. A continuous analog voltage
proportional to the tab temperature is produced at the OUT terminal and can control linearly an external
PNP transistor (Fan Transistor) connected in series with a Brushless DC Fan, in order to vary its speed.
The ON control terminal can be used to select two operation modes. If not connected (high impedance
state) ON mode is selected by default.
In Mode ON, the fan speed is regulated according to the tab temperature of the FSCT by adjusting the Vbe
voltage of the PNP fan Transistor. In low temperature conditions, the fan transistor voltage is limited to
about 5.5V (for a 12V fan) in order to guarantee a minimum voltage across the fan above its stalling voltage
and to keep it running (see figure 3).
This regulation is implemented with a high Fan supply voltage rejection.
The mode OFF allows to operate in green Mode. The fan is stopped as long as the temperature remains
below the TON threshold. When the temperature rises above TON the fan is forced to ON and the speed is
regulated according to the temperature as in the same way as mode ON. When temperature falls below
TOFF, the fan is automatically turned OFF. The hysteresis has been dimensioned large enough to reduce
ON/OFF oscillations during the green mode operation.
May 2003 - Ed: 1A
1/11
FSCTxxA-UH5
PINT OUT DESIGNATION
Pint Out
designation
Description
Pin
TEST
Test pin (must not be connected)
1
VCC
Operating DC supply
2
GND
Ground (internally connected to the tab)
3
ON
Mode ON and OFF selection
4
OUT
Output (connect to PNP fan transistor base)
5
ABSOLUTE MAXIMUM RATINGS
Symbol
VCC
Tj
Tstg
TL
ESD
Parameter
Value
Unit
-0.3 to 20
V
0 to 125
°C
-65 to 150
°C
Lead temperature (double wave soldering)
260
°C
Maximum voltage at any pin
VCC
V
Minimum voltage at any pin
-0.3
V
2
kV
Supply voltage referenced to GND
Operating junction temperature
Storage temperature
Electrostatic discharge immunity at each terminal
(human body model)
ELECTRICAL CHARACTERISTICS (Continue)
VCC from 9Vdc to 15Vdc, Cout = 100nF, Tj = 0°C to 125°C, otherwise specified
Symbol
Parameter
Test conditions
Value
Min.
Typ.
Max.
1.1
3
Unit
SUPPLY
ICCmax
Operating supply current VON = 5V or 0V
VCC = 12V
mA
DRIVER
IOL
Sinking current capability VOUT = VOL and Tj = 125°C
at the OUT terminal
ILEAK
Maximum sink leakage
VOUT = 20V, VON = 0V
current at OUT pin (mode Tj = 50°C
OFF)
VOL
Minimum voltage at the
VON = 5V, Tj = 125°C
OUT terminal (mode ON)
OUT voltage for minimum fan speed (mode
ON)
VOMS
KSL
2/11
10
mA
10
µA
0.55
0.7
V
VON = 5V, Tj from 0°C to TMS
5.3
5.5
V
Static line regulation
VCC = 9V to 15V, VON = 5V
Tj = 25°C
0.5
VOUT temperature slope
VOUT = 80% FSCT17A-UH5
VOMS to
FSCT11A-UH5
20% VOMS
FSCT07A-UH5
mV/V
155
165
175
100
107
114
68
72
77
mV/°C
FSCTxxA-UH5
ELECTRICAL CHARACTERISTICS (Continue)
VCC within the supply voltage range, Cout = 100nF, Tj = 0°C to 125°C, otherwise specified
Symbol
Parameter
Value
Test conditions
Min.
Typ.
TEMPERATURE MANAGEMENT (all T° threshold are guaranteed by design)
Max.
Unit
TMS
Temperature regulation VOUT = VOMS
VON = 5V
threshold
32
37
42
°C
TON
OFF mode switch ON
temperature
VCC = 12V
VON = 0V
66
71
76
°C
TOFF
OFF mode switch OFF
temperature
VCC = 12V
VON = 0V
34
39
44
°C
TOL
Minimum temperature
for maximum speed
VCC = 12V
VON = 5V
VOUT = VOL
FSCT17A-UH5
61
66
71
°C
FSCT11A-UH5
76
81
86
FSCT07A-UH5
97
102
107
FSCT17A-UH5
49
52
55
FSCT11A-UH5
56
59
62
FSCT07A-UH5
66
69
72
TV3
Tab temperature for
VOUT = 3V (*)
(see figure 3)
VOUT = 3V
VON = 5V
°C
ON SIGNAL
VIH
Voltage range for ON mode
VIL
Voltage range for OFF mode
IS
Source current at the
ON pin (see figure 2)
VCC = 12V
ON terminal shorted to ground
1
V
10
0.3
V
25
µA
(*) +/- 3°C absolute temperature dispersion applicable on all VOUT range between VOMS and VOL
THERMAL PARAMETERS
Symbol
Rth(j-c)
Parameter
Thermal resistance junction to case
Value
Unit
3
°C/W
Fig. 2: "ON" input schematic diagram.
VCC
IS
To other blocks
50k
ON
3/11
FSCTxxA-UH5
Fig. 3: Temperature slopes.
VOUT(VDC)
VOMS = 5.3V
5
UH
A17 /°C
CT mV
FS 165
FS
CT
11
FS
CT
7m A-U
0
H5
V/
72 7A-U
°C
mV
H
/°C 5
10
VOUT = 3V
VOL = 0.6V
Tj(°C)
TMS=37
TV3 TOL=66
TV3 TOL=81
TOL=102
TV3
Fig. 4: ICC versus VCC for mode ON.
Fig. 5: ICC versus VCC test circuit (mode ON).
VCC
ICC(mA)
A
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
ICC
Tj = 25°C
VON 1V
Tj = 125°C
3.8k
ON
Test
9
11
13
15
VCC(V)
4/11
VFAN 12V
17
19
VCC
OUT
GND
100nF
FSCTxxA-UH5
DETAILED DESCRIPTION & APPLICATION INFORMATION
1. OUTPUT CHARACTERISTIC VERSUS TEMPERATURE
1.1 FAN speed control
As it's well known, BRUSHLESS DC motors present the advantage of a quasi-linear speed-voltage characteristic. Hence, the fan speed is varying linearly versus the voltage which is applied across its terminals.
The FSCT Integrated Circuit provides at its OUT terminal, a voltage which changes versus the temperature
sensed through its tab. This OUT voltage decreases as temperature increases, following two modes of operation. By connecting this OUT terminal to the Base of a PNP transistor, as shown in figure 1, the FAN
voltage will increase with the sensed temperature.
The FAN voltage is given by the following equation: V FAN = V FAN + − V EB − V OUT (1)
Typically, for a 12 V VFAN+ and a 1 V VEB voltage, this gives: V FAN (V ) = 11 − V OUT (V ) (2)
It can be noticed that the PNP operates as a linear amplifier. This avoids EMI and acoustic noise compared
to Pulse Width Modulation control circuits.
1.2 ON/OFF Mode Selection
The figure 6 gives the algorithm flowchart of the FSCT behavior. First, two modes of operation are distinguished by the ON pin signal.
Mode ON: activated when ON pin is at High Level or Not Connected (thanks to an internal Pull-up
curren source "IS")
Mode OFF: activated when ON pin is at Low Level.
■
■
During Mode ON, the OUT voltage follows a three-parts characteristic, according to its junction temperature (Tj):
Tj < TMS: in this case, VOUT is limited to VOMS to avoid stalling the fan rotor
TMS < Tj < TOL: VOUT is linearly regulated versus the junction temperature
Tj > TOL: in this case, VOUT is clamped to its minimum value (VOL).
■
■
■
During Mode OFF, an Hysteresis control allows
the system to switch to mode ON only if the temperature exceeds the TON value. The Fan is turned
back off, if the system is cooled enough to lower
the temperature below TOFF.
The figure 7 sums up the FSCT Output characteristic versus the temperature, for the two operation
modes.
1.3 Minimum speed (mode ON)
Mode ON allows users to ensure that the FAN will
be always ON, whatever the ambient temperature
is.
The OUT voltage is clamped to VOMS for low temperature (below TMS = 37 °C typically).
The VOMS has been set to 5.5 V max , thus the
minimum voltage applied across the FAN is 5.5 V
(according to Equation 2). This voltage is above
stalling value of most fans and will then ensure that
the controlled FAN will always run, in mode ON,
avoiding spurious turn-off due to too low voltage at
low temperature. Annoying noises due to FAN
repetitive starts up are also suppressed.
Fig. 6: FSCT behavior flow-chart.
BEGIN
ON is
LOW
?
yes
FAN OFF (V OUT = V CC)
no
Tj > T ON
?
no
yes
FAN ON
VOUT = V OMS – kSL.(Tj – TMS)
OR
VOUT = V OMS IF Tj < T MS
OR
VOUT = V OL IF Tj > T OL
FAN ON
VOUT = V OMS – kSL.(Tj – TMS)
OR
VOUT = V OL IF Tj > T OL
Tj < T OFF
?
no
yes
FAN OFF
VOUT = V CC
5/11
FSCTxxA-UH5
2. Hysteresis control (mode OFF)
FSCT can be shut down by the ON signal. When, this signal is low, the OUT pin is at high level, i.e. the FAN
is turned off.
This mode enables to save the energy wasted by the FAN in case of operations at very low output power.
For a 12 V supply voltage, the shut-down of the FAN brings a 0.5 to 2.5 W power saving (for a 200 mA 12 V
DC motor).
During the mode OFF, the FSCT doesn't lose temperature control; indeed, in case of over-temperature,
the FAN is automatically switched on. This safety feature protects the power supply or the semiconductor
devices from unexpected over-temperature.
In order to keep the energy saving benefit, the FSCT turns back off the FAN when the temperature falls below TOFF threshold.
In practice, three cases can appear for a constant applied heating power (for instance, the output power of
the power supply where the FSCT is used) (cf. figure 8):
Case 1: the heating power is too low, and keeps Tj below TON. The FAN remains OFF.
Case 2: the heating power is high enough to raise Tj above TON. But, as this power is quite low, Tj falls
down TOFF, and the temperature starts again to increase, up to TON. This results in a FAN ON/OFF periodical cycle.
Case 3: the heating power is higher that in case 2, so that Tj remains above TOFF. The FAN stays ON
in that case, unless the heating power decreases.
For example, with a 200 W computer power supply, working with a FSCT17 device put on the power semiconductors heatsink, Case 1 could be reached for a 25 W output power consumption (Tj will stabilize
around 60 °C, i.e. below typical TON).
Case 2 could be reached for a 50 W power consumption. Then, thanks to the large Hysteresis value (30 °C
typ.), the ON/OFF period (refer to TP on figure 8) lasts approximately 15 minutes. This is long enough to
avoid too many FAN starts-up cycle per hour.
Case 3 could be reached for a 75W, or higher, power consumption. For 75W, the power supply ambient
temperature stabilizes itself around 42°C.
It should be noted that, for Case 3, such steady state points of operation, are allowed due to the fact that the
OUT voltage follows the same linear law as that in ON mode. Then, the Hysteresis control is smarter than a
simple ON/OFF control mode.
■
■
■
Fig. 7: OUT voltage versus junction temperature.
VOUT
VCC
Mode OFF
VOMS
Mode ON
VOL
TMS
6/11
TOFF TOL
TON
Tj(°C)
FSCTxxA-UH5
Fig. 8: Temperature evolution cases in mode OFF.
Tj
TP
TON
TOFF
3
2
1
Time
3. Internal temperature sensor
3.1 Temperature sensor linear response
FSCT devices feature an internal temperature sensor. This sensor results directly from silicon properties. It
is actually a voltage reference which is proportional to the absolute temperature, as it is an image of the Silicon thermal voltage "Vt" (refer to the following equation).
k : Boltzmann cons tant
k ⋅T
with: T : absolute temperature (K )
Vt =
q
q = 16
. ⋅ 10 −19C
This sensing method, which presents a positive temperature coefficient of +2mV/°C is preferred to a VBE
sensing method (-2mV/°C, sometimes used in thermal protections) because of its better accuracy (low impact of process dispersions).
This signal is then processed to provide the desired OUT voltage range.
This internal sensor allows users not to use a Negative Temperature Coefficient thermistor (NTC).
Hence, users get rid of Joule effect, due to NTC bias current, that disturbs the temperature measurement.
Furthermore, the FSCT response is linear with the temperature. This simplifies the thermal study and the
heat sink rating for the power supply components or for the microprocessor.
NTC thermistors users need also to add a fixed resistor in order to get a linear thermal response from such
kind of sensor. The linear behavior is also only ensured for a restricted temperature range.
3.2 IPPAK mounting considerations
First, it should be noted that the tab is directly connected to the GND pin; then care must be taken when the
FSCT is glued to a heatsink. If this heatsink is at a differential voltage that the Ground, an electrical insulator has to be added between the tab and the heat-sink.
Using non-isolated Through-Hole package like the IPPAK offers also a lot of benefits, compared to NTC
bulbs. Indeed, NTC do not offer a flat area like IPPAK package. Users need to add some glue to ensure
contact of the NTC bulb and the heat sink, at the cost of an increase in the thermal impedance and
response.
7/6
FSCTxxA-UH5
Two components should be used to improve the heat exchange between the FSCT die and the heat sink,
that the temperature has to be monitored. These components are:
A thermal interface pad, in order to reduce the impact of air voids on the thermal impedance and to ensure an electrical insulation (if needed)
A clip to push the IPPAK against the heat sink and then to reduce also the interface thermal impedance.
Several clips can be used depending on the heat sink type:
Saddle clips (cf. figure 9) for slim heat sink;
U-clips (cf. figure 10) for thick heat sink
Dedicated clips for special shape heat sink.
■
■
■
■
■
Fig. 9: IPPAK mounted with a Saddle clip.
Fig. 10: IPPAK mounted with a U-clip.
It can be noticed that the thickness of the IPPAK package (2.3 +/- 0.1 mm) is similar to those of SOT-32 and
SOT-82 (2.55 +/- 0.15 mm). The same clips can so be used for all these packages.
3.3 Temperature measurement error
Firstly, the time constant between a temperature variation on the external side on the IPPAK tab, and the
silicon die is in the range of a few hundred of milliseconds. As temperature phenomena are extremely slow
for the targeted applications (the temperature of a MOSFET heat sink, increases typically with an 1°C per
second rate, in a power supply), the FSCT is able to react immediately to over-heating events.
Moreover, the very low junction to case thermal resistance (3 °C/W) reduces as much as possible the temperature measurement error.
We calculate, in the following, this error considering both the package and the heatsink-Tab interface thermal resistances (figure 11).
Several companies offer adhesive and isolating
materials to be used as interface between electronic devices and a heat sink. These interfaces
can be provided with a shape dedicated for the
Tab foot print. For the IPPAK package, users could
choose a shape dedicated for SOT-32, SOT-82 or
even TO-126 or TO-220 packages (the more can
do the less).
8/11
Fig. 11: IPPAK Heatsink Interface.
Interface
FSCTxxA-UH5
These interfaces offer very low thermal resistance. For example, the Sil-Pad® 800 family, from
BERGQUIST, which is designed for low cost applications and low mounting pressures, present a typical
thermal impedance of 0.45 °C.in²/W. This impedance can increase up to 0.92 °C.in²/W for a 10 psi pressure, which is below the normal atmospheric one (1 atm = 1013 hPa = 1013 x 15.4 x 10-3 = 15.6 psi).
Furthermore, a mounting clip will apply a force between 15 to 50 N. This leads to a 25 to 200 psi pressure.
In this case, the thermal impedance varies from 0.6 to 0.29 °C.in²/W for the Sil-Pad® 800 family.
For the example, we take the worst case hypothesis of a 1°C.in²/W interface between the FSCT case and
the heat sink.
We take into account only the tab surface for the heat exchange. This surface equals typically:
S = 4.7 x 5.1 mm2 = 0.037 in2
This yields to a supplementary resistance of: Rthc-h = 1/0.037 = 27°C/W
Then, the maximum power dissipated in the FSCT, for the maximum output power, is given by the following
equation:
Pmax = I CC ⋅ V CC + I OUT ⋅ V OMS
The following numerical application gives (for a 150 mA FAN DC current, a 80 gain for the PNP and a 12 V
power supply):
IOUT = 150 / 80 = 1.87mA
Pmax = 3 × 12 × 10 −3 + 187
. × 5.5 × 10 −3 = 46mW
Then, the temperature error is: ∆T = 0.046 × (3 + 27 ) = 138
. °C
The temperature sensing error can then be neglected whan one considers the operation range (from 0 to
100 °C), even with low cost interface material and without any mounting clip. For example, with a higher
pressure, thanks to a clip, this error could be divided by three.
4. TEMPERATURE/VOLTAGE SLOPE CHANGE
The OUT voltage versus temperature characteristic of the FSCT has been designed to fit majority cases of
application, in the field of PC power supplies.
The advantage for the user is to have a minimum count of components while achieving a smart
temperature regulation.
Nevertheless, some applications require dedicated temperature regulation characteristic. Figure 13
provides an example of a solution which allows to change the ratio between PNP base voltage and the
temperature. This schematic only requires a dual
Fig. 12: Modified characteristics.
single-voltage amplifier (in DIL8 package for
example) and less than ten supplementary
resistors.
VOUT
This schematic keeps the advantage of applying a
VNEW
constant minimum voltage (VOMS) below TMS temperature. Indeed, the U1A operational amplifier
subtracts 5.1 V (thanks to the D1 Zener diode, refer to VREF) from VOUT. This means that the ratio
Mode OFF
change is only taken into account when VOUT is
VOMS
lower than 5.1 V. For higher voltages (VOMS in mode
Mode ON
ON or VCC in mode OFF), the new base to GND voltage (VNEW) remains the same (cf. figure 12).
Step-down
So, if one wants to increase accurately the
voltage-temperature ratio, i.e. that VOUT will
decrease more quickly when Tj increases, figure
TOFF
TON
Tj(°C)
13 schematics should be implemented. Indeed,
the voltage at the operational amplifier U1B (which
acts as a follower) output is:
V NEW = V OUT if V OUT > V REF
RN
V NEW = V OUT − RD ⋅ (V REF − V OUT ) otherwise
9/11
FSCTxxA-UH5
Fig. 13: Step-down OUT voltage schematic.
PARAMETERS:
RD = 33k
RN = 68k
RF = 130k
VCC
VCC
R2
{RN}
1
M1
U2
R1
5
U1A
4
{RD}
ON
TEST
2
R6
1
3
FAN MOTOR
R9
{RF}
GND
8
3
MC33172
2
OUT
+
4
1
VCC
-
2
FSCT
VCC
{RF}
U1B
VCC
R7
5V1
10/11
C1
VREF
2N2907
{RF}
{RD}
DZ
Q1
+
R4
MC33172
7
5
R3
1k
-
6
2n2
R5
{RN}
VOUT
R8
{RF}
VNEW
FSCTxxA-UH5
PACKAGE MECHANICAL DATA
IPPAK
DIMENSIONS
REF.
Millimeters
Min.
E
A
B2
C2
L2
D
L1
H
B3
B
B6
L
A1
V1
C
e
B5
G1
G
Order code
Marking
FSCT17A-UH5
FSCT17A
FSCT11A-UH5
FSCT11A
FSCT07A-UH5
FSCT07A
A
A1
B
B2
B3
B5
B6
C
C2
D
E
e
G
G1
H
L
L1
L2
V1
Typ.
2.20
0.90
0.40
5.20
Inches
Max
Min.
2.40
1.10
0.60
5.40
0.70
0.086
0.035
0.015
0.204
0.30
0.094
0.043
0.023
0.212
0.027
0.039
0.023
0.023
0.244
0.259
0.017
0.018
0.236
0.215
1.27
4.9
2.38
15.90
9.00
0.80
Max.
0.011
1.00
0.60
0.60
6.20
6.60
0.45
0.48
6.00
6.40
Typ.
0.050
5.25
2.70
16.30
9.40
1.20
0.80 1.00
10°
0.192
0.093
0.625
0.354
0.031
0.206
0.106
0.641
0.370
0.047
0.031 0.039
10°
Package
Weight
Delivery mode
Base qty
IPPAK
0.4 g
Tube
75
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of
use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by
implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to
change without notice. This publication supersedes and replaces all information previously supplied.
STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics
© 2003 STMicroelectronics - Printed in Italy - All rights reserved.
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11/11