LTC3541EDD#TRPBF【PDF 15/20 页】IC REG DL BCK/LINEAR SYNC 10-DFN

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LTC3541

3541fa

PPLICATIO S I FOR ATIO

proportional to frequency. Both the DC bias and gate charge

losses are proportional to V

and thus their effects will

be more pronounced at higher supply voltages.

2. I

R losses are calculated from the resistances of the

internal switches, R

, and external inductor R

. In con-

tinuous mode, the average output current flowing through

inductor L is chopped between the main switch and the

synchronous switch. Thus, the series resistance looking

into the SW pin is a function of both top and bottom

MOSFET R

DS(ON)

and the duty cycle (DC) as follows:

= (R

DS(ON)TOP

)(DC) + (R

DS(ON)BOT

)(1 DC)

The R

DS(ON)

for both the top and bottom MOSFETs can

be obtained from the Typical Performance Characteristics

curves. Thus, to obtain I

R losses, simply add R

and multiply the result by the square of the average

output current.

3. Losses in the VLDO/linear regulator are due to the DC bias

currents as given in the Electrical Characteristics and to the

OUT

) voltage drop across the internal output device

transistor.

Other losses when the buck and VLDO are in operation

(ENBUCK and ENVLDO equal logic high), including C

and C

OUT

ESR dissipative losses and inductor core losses,

generally account for less than 2% total additional loss.

THERMAL CONSIDERATIONS

The LTC3541 requires the package backplane metal (GND

pin) to be well soldered to the PC board. This gives the

DFN package exceptional thermal properties. The power

handling capability of the device will be limited by the

maximum rated junction temperature of 125癈. The

LTC3541 has internal thermal limiting designed to protect

the device during momentary overload conditions. For

continuous normal conditions, the maximum junction

temperature rating of 125癈 must not be exceeded. It is

important to give careful consideration to all sources of

thermal resistance from junction to ambient. Additional

heat sources mounted nearby must also be considered.

For surface mount devices, heat sinking is accomplished

by using the heat-spreading capabilities of the PC board

and its copper traces. Copper board stiffeners and plated

through holes can also be used to spread the heat gener-

ated by power devices.

To avoid the LTC3541 exceeding the maximum junction

temperature, some thermal analysis is required. 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:

= P

" ?/DIV>

where P

is the power dissipated by the regulator and ?/DIV>

is the thermal resistance from the junction of the die to

the ambient temperature.

The junction temperature, T

, is given by:

= T

+ T

where T

is the ambient temperature.

As an example, consider the LTC3541 with an input voltage

of 2.9V, an LV

voltage of 1.8V, an LV

OUT

voltage of

1.5V, a load current of 200mA for the buck, a load cur-

rent of 300mA for the VLDO and an ambient temperature

of 85癈. From the typical performance graph of switch

resistance, the R

DS(ON)

of the P-channel switch at 85癈 is

approximately 0.25?The R

DS(ON)

of the N-channel switch

is approximately 0.4? Therefore, power dissipated by the

part is approximately:

= (I

LOADBUCK

)

" R

+ (I

LOADVLDO

)

(LV

OUT

) = 167mW

For the 3mm ?3mm DFN package, the ?/DIV>

is 43癈/W.

Thus, the junction temperature of the regulator is:

= 85癈 + (0.167)(43) = 92癈

which is well below the maximum junction temperature

of 125癈.

Note that at higher supply voltages, the junction tempera-

ture is lower due to reduced switch resistance R

DS(ON)

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LTC3541EDD-1#PBF 功能描述:IC REG DL BCK/LINEAR SYNC 10-DFN RoHS:是类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2）功能:任何功能输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器电压/电流 - 输出 2:控制器电压/电流 - 输出 3:控制器带 LED 驱动器:无带监控器:无带序列发生器:是电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*

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LTC3541EDD-1-PBF 制造商:LINER 制造商全称:Linear Technology 功能描述:High Efficiency Buck + VLDO Regulator

LTC3541EDD-1-TRPBF 制造商:LINER 制造商全称:Linear Technology 功能描述:High Efficiency Buck + VLDO Regulator

LTC3541EDD-2 制造商:LINER 制造商全称:Linear Technology 功能描述:High Efficiency Buck + VLDO Regulator

LTC3541EDD-2#PBF 功能描述:IC REG DL BCK/LINEAR SYNC 10-DFN RoHS:是类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2）功能:任何功能输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器电压/电流 - 输出 2:控制器电压/电流 - 输出 3:控制器带 LED 驱动器:无带监控器:无带序列发生器:是电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*

LTC3541EDD-2#TRPBF 功能描述:IC REG DL BCK/LINEAR SYNC 10-DFN RoHS:是类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2）功能:任何功能输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器电压/电流 - 输出 2:控制器电压/电流 - 输出 3:控制器带 LED 驱动器:无带监控器:无带序列发生器:是电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*

LTC3541EDD-3 制造商:LINER 制造商全称:Linear Technology 功能描述:High Efficiency Buck + VLDO Regulator

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