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参数资料
| 型号： | LTC3546EUFD |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 4000 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封装： | 4 X 5 MM, PLASTIC, MO-220, QFN-28 |
| 文件页数： | 15/28页 |
| 文件大小： | 356K |
| 代理商： | LTC3546EUFD |
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LTC3546
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APPLICATIONS INFORMATION
tion to exceed the maximum junction temperature of the
part. In a majority of applications, the LTC3546 does not
dissipate much heat due to its high efciency. However, in
applications where the LTC3546 is running at high ambient
temperature with low supply voltage and high duty cycles,
such as in dropout, the heat dissipated may exceed the
maximum junction temperature of the part. If the junction
temperature reaches approximately 150°C, both switches
in both regulators will be turned off and the SW nodes will
become high impedance.
To avoid the LTC3546 from exceeding the maximum junc-
tion temperature, the user will need to do some thermal
analysis. The goal of the thermal analysis is to determine
whether the power dissipated exceeds the maximum
junction temperature of the part. The temperature rise is
given by:
TRISE = PD θJA
where PD is the power dissipated by the regulator and θJA
is the thermal resistance from the junction of the die to
the ambient temperature.
The junction temperature, TJ, is given by:
TJ = TRISE + TAMBIENT
As an example, consider the case when the LTC3546 is
in dropout in both regulators at an input voltage of 3.3V
with load currents of 3A (SW1D externally connected to
SW2) and 1A. From the Typical Performance Character-
istics graph of Switch Resistance, the RDS(ON) resistance
of the 3A P-channel switch parallel combination of SW2
and SW1D is 0.06Ω and the RDS(ON) of the 1A P-channel
switch is 0.18Ω. The power dissipated by the part is:
PD = I12 RDS(ON)1 + I22 RDS(ON)2
PD = 32 0.064 + 12 0.19
PD = 0.77W
The UFD package junction-to-ambient thermal resistance,
θJA, is about 34°C/W. Therefore, the junction temperature
of the regulator operating in a 85°C ambient temperature
is approximately:
TJ = 0.77 34 + 85
TJ = 111.2°C
This junction temperature is obtained from an RDS(ON) at
25°C. At 125°C the RDS(ON) increases by about 30%. This
will put the junction temperature at 122°C. If the supply is
lower, like 2.25V, the RDS(ON) is higher still. Special care
needs to be taken if the part is expected to be operating
in dropout so that the maximum junction temperature of
125°C is not exceeded.
Design Example
As a design example, consider using the LTC3546 in a
portable application with a Li-Ion battery. The battery
provides a VIN = 2.25V to 4.2V. One output requires 1.8V
at 2.5A in active mode, and 1mA in standby mode. The
other output requires 1.2V at 800mA in active mode,
and 500μA in stand-by mode. Since both loads still need
power in stand-by, Burst Mode operation is selected for
good low load efciency.
First, determine what frequency should be used. Higher
frequency results in a lower inductor value for a given ΔIL
(ΔIL is estimated as 0.35ILOAD(MAX)). Reasonable values
for wire wound surface mount inductors are in the 1μH
and up. Look at the different frequencies with the ΔIL =
0.35ILOAD(MAX).
CONVERTER OUTPUT
ILOAD(MAX)
ΔIL
SW2/SW1D, 1.2V
2.5A
875mA
SW1, 1.8V
800mA
280mA
Using the 1.5MHz frequency setting (FREQ = 143k to GNDA)
we get the following equations for L1 and L2.
L1=
1.2V
1.5MHz 280mA
1
1.2V
4.2V
= 2H
L2 =
1.8V
1.5MHz 875mA
1
1.8V
4.2V
= 0.78H
Use 1μH and 2.2μH.
COUT selection is typically based on load step rather
than the ripple requirements. The minimum required
capacitance will increase with a decrease in compensa-
tion loop bandwidth and/or increases in maximum load
step or output voltage tolerance. A good starting point is
about 22μF per ampere of output current for a nominal
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| LTC3546EUFD#PBF | 功能描述:IC REG BUCK SYNC ADJ 1A/2A 28QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:MIC23xxx HyperLight Load™ Regulators 标准包装:5,000 系列:HyperLight Load® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.8V 输入电压:2.7 V ~ 5.5 V PWM 型:混合物 频率 - 开关:4MHz 电流 - 输出:2A 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘，8-MLF? 包装:带卷 (TR) 供应商设备封装:8-MLF?（2x2） 产品目录页面:1094 (CN2011-ZH PDF) 其它名称:576-3303-2 |
| LTC3546EUFD#TRPBF | 功能描述:IC REG BUCK SYNC ADJ 1A/2A 28QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LTC3546EUFDPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Synchronous, 3A/1A or 2A/2A Confi gurable Step-Down DC/DC Regulator |
| LTC3546EUFDTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Synchronous, 3A/1A or 2A/2A Confi gurable Step-Down DC/DC Regulator |
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