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| 型号： | MIC2585-1MYTS |
| 厂商： | Micrel Inc |
| 文件页数： | 25/28页 |
| 文件大小： | 273K |
| 描述： | IC CTRLR HOT SWAP DUAL 24-TSSOP |
| 标准包装： | 62 |
| 类型： | 热交换控制器 |
| 应用： | 通用 |
| 内部开关： | 无 |
| 电源电压： | 1 V ~ 13.2 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 24-TSSOP |
| 包装： | 管件 |
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March 2005
25
MIC2584/2585
MIC2584/2585
Micrel
higher pulsed power without damage than its continuous
dissipation ratings would imply. The reason for this is that, like
everything else, thermal devices (silicon die, lead frames,
etc.) have thermal inertia.
In terms related directly to the specification and use of power
MOSFETs, this is known as transient thermal impedance,
or Z
?J-A)
. Almost all power MOSFET data sheets give a
Transient Thermal Impedance Curve. For example, take the
following case: V
IN
= 12V, t
OCSLOW
has been set to 100msec,
I
LOAD(CONT. MAX)
is 1.2A, the slow-trip threshold is 50mV
nominal, and the fast-trip threshold is 100mV. If the output is
accidentally connected to a 6& load, the output current from
the MOSFET will be regulated to 1.2A for 100ms (t
OCSLOW
)
before the part trips. During that time, the dissipation in the
MOSFET is given by:
P = E x I E
MOSFET
= [12V-(1.2A)(6&)] = 4.8V
P
MOSFET
= (4.8V x 1.2A) = 5.76W for 100msec.
At first glance, it would appear that a really hefty MOSFET is
required to withstand this sort of fault condition. This is where
the transient thermal impedance curves become very useful.
Figure 13 shows the curve for the Vishay (Siliconix) Si4410DY,
a commonly used SO-8 power MOSFET.
Taking the simplest case first, well assume that once a fault
event such as the one in question occurs, it will be a long time,
10 minutes or more, before the fault is isolated and the
channel is reset. In such a case, we can approximate this as
a single pulse event, that is to say, theres no significant duty
cycle. Then, reading up from the X-axis at the point where
Square Wave Pulse Duration is equal to 0.1sec (=100msec),
we see that the Z
?J-A)
of this MOSFET to a highly infrequent
event of this duration is only 8% of its continuous R
?J-A)
.
This particular part is specified as having an R
?J-A)
of
50癈/W for intervals of 10 seconds or less. Thus:
Assume T
A
= 55癈 maximum, 1 square inch of copper at the
drain leads, no airflow.
Recalling from our previous approximation hint, the part has
an R
ON
of (0.0335/2) = 17m& at 25癈.
Assume it has been carrying just about 1.2A for some time.
When performing this calculation, be sure to use the highest
anticipated ambient temperature (T
A(MAX)
) in which the
MOSFET will be operating as the starting temperature, and
find the operating junction temperature increase (T
J
) from
that point. Then, as shown next, the final junction temperature
is found by adding T
A(MAX)
and T
J
. Since this is not a closed-
form equation, getting a close approximation may take one or
two iterations, But its not a hard calculation to perform, and
tends to converge quickly.
Then the starting (steady-state)T
J
is:
T
J
E T
A(MAX)
+ T
J
E T
A(MAX)
+ [R
ON
+ (T
A(MAX)
T
A
)(0.005/癈)(R
ON
)]
x I
2
x R
?J-A)
T
J
E 55癈 + [17m& + (55癈-25癈)(0.005)(17m&)]
x (1.2A)
2
x (50癈/W)
T
J
E (55癈 + (0.02815W)(50癈/W)
E 54.6癈
Iterate the calculation once to see if this value is within a few
percent of the expected final value. For this iteration we will
start with T
J
equal to the already calculated value of 54.6癈:
T
J
E T
A
+ [17m& + (54.6癈-25癈)(0.005)(17m&)]
x (1.2A)
2
x (50癈/W)
T
J
E ( 55癈 + (0.02832W)(50癈/W) E 56.42癈
So our original approximation of 56.4癈 was very close to the
correct value. We will use T
J
= 56癈.
Finally, add (5.76W)(50癈/W)(0.08) = 23癈 to the steady-state
T
J
to get T
J(TRANSIENT MAX.)
= 79癈. This is an acceptable
maximum junction temperature for this part.
2
1
0.1
0.01
10
4
10
3
10
2
10
1
1
10
30
0.2
0.1
0.05
0.02
Single Pulse
Duty Cycle = 0.5
1. Duty Cycle, D =
2. Per Unit Base = R
thJA
= 50?/SPAN>C/W
3. T
JM
T
A
= P
DM
Z
thJA
(t)
t
1
t
2
t
1
t
2
Notes:
4. Surface Mounted
P
DM
Normalized Thermal Transient Impedance, Junction-to-Ambient
Square Wave Pulse Duration (sec)
Figure 13. Transient Thermal Impedance
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MIC2585-1MYTS TR | 功能描述:热插拔功率分布 Dual Channel Hot-Swap Controller - 100mV Threshold (Lead Free) RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube |
| MIC2585-2JBTS | 功能描述:IC CTRLR HOT SWAP DUAL 24-TSSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:100 系列:- 类型:热插拔开关 应用:通用 内部开关:是 电流限制:可调 电源电压:9 V ~ 13.2 V 工作温度:-40°C ~ 150°C 安装类型:表面贴装 封装/外壳:10-WFDFN 裸露焊盘 供应商设备封装:10-TDFN-EP（3x3） 包装:管件 |
| MIC2585-2JBTS TR | 功能描述:IC CTRLR HOT SWAP DUAL 24-TSSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:100 系列:- 类型:热插拔开关 应用:通用 内部开关:是 电流限制:可调 电源电压:9 V ~ 13.2 V 工作温度:-40°C ~ 150°C 安装类型:表面贴装 封装/外壳:10-WFDFN 裸露焊盘 供应商设备封装:10-TDFN-EP（3x3） 包装:管件 |
| MIC2585-2JYTS | 功能描述:热插拔功率分布 Dual Channel Hot-Swap Controller - 100mV Threshold - Lead Free RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube |
| MIC2585-2JYTS TR | 功能描述:热插拔功率分布 Dual Channel Hot-Swap Controller - 100mV Threshold - Lead Free RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube |
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