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参数资料
| 型号： | L7981ATR |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, DSO8 |
| 封装： | 3 X 3 MM, 1.08 MM HEIGHT, ROHS COMPLIANT, HSOP-8 |
| 文件页数： | 21/44页 |
| 文件大小： | 1315K |
| 代理商： | L7981ATR |
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Application informations
L7981
28/44
Doc ID 15182 Rev 3
6.5
Thermal considerations
The thermal design is important to prevent the thermal shutdown of device if junction
temperature goes above 150°C. The three different sources of losses within the device are:
a)
conduction losses due to the not negligible RDSon of the power switch; these are
equal to:
Equation 29
Where D is the duty cycle of the application and the maximum RDSon over temperature is
220 m
Ω. Note that the duty cycle is theoretically given by the ratio between V
OUT and VIN,
but actually it is quite higher to compensate the losses of the regulator. So the conduction
losses increases compared with the ideal case.
b)
switching losses due to power MOSFET turn ON and OFF; these can be
calculated as:
Equation 30
Where TRISE and TFALL are the overlap times of the voltage across the power switch (VDS)
and the current flowing into it during turn ON and turn OFF phases, as shown in Figure 16.
TSW is the equivalent switching time. For this device the typical value for the equivalent
switching time is 30 ns.
c)
Quiescent current losses, calculated as:
Equation 31
where IQ is the quiescent current (IQ=2.4 mA).
The junction temperature TJ can be calculated as:
Equation 32
Where TA is the ambient temperature and PTOT is the sum of the power losses just seen.
RthJA is the equivalent thermal resistance junction to ambient of the device; it can be
calculated as the parallel of many paths of heat conduction from the junction to the ambient.
For this device the path through the exposed pad is the one conducting the largest amount
P
ON
R
DSON
I
OUT
()
2
D
=
P
SW
V
IN
I
OUT
T
RISE
T
FALL
+
()
2
------------------------------------------- Fsw
V
IN
I
OUT
T
SW
F
SW
==
P
Q
V
IN
I
Q
=
T
J
T
A
Rth
JA
P
TOT
+
=
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L7981ATR/BLK | 制造商:STMicroelectronics 功能描述:3 A STEP-DOWN SWITCHING REGULATO - Tape and Reel 制造商:STMicroelectronics 功能描述:STMicroelectronics L7981ATR/BLK Interface Misc |
| L7981TR | 功能描述:直流/直流开关调节器 3A DC 4.5 V to 28 V Adj 0.6V 250 kHz RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| L7983 | 制造商:Leviton Manufacturing Co 功能描述: |
| L7985 | 功能描述:线性稳压器 - 标准 2A Step Down REG 4.5V to 38V 250 KHz RoHS:否 制造商:STMicroelectronics 输出类型: 极性: 输出电压:1.8 V 输出电流:150 mA 负载调节: 最大输入电压:5.5 V 线路调整率: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOT-323-5L |
| L7985A | 功能描述:直流/直流开关调节器 2A DC 4.5V to 38V 250 KHz Step-Down RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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