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| 型号： | LTC3634EUFD#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 5.5 A DUAL SWITCHING CONTROLLER, 4600 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封装： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件页数： | 14/28页 |
| 文件大小： | 359K |
| 代理商： | LTC3634EUFD#TRPBF |
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LTC3634
21
3634f
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can
be expressed as:
% Efficiency = 100% – (L1 + L2 + L3 +…)
where L1, L2, etc. are the individual losses as a percentage
of input power. Although all dissipative elements in the
circuitproducelosses,threemainsourcesusuallyaccount
for most of the losses in LTC3634 circuits: 1) conduction
losses, 2) switching losses and quiescent power loss 3)
transition losses and other losses.
1. Conduction losses are calculated from the DC resis-
tances of the internal switches, RSW, and external
inductor, RL. In continuous mode, the average output
current flows through inductor L but is “chopped”
between the internal top and bottom power MOSFETs.
Thus, the series resistance looking into the SW pin is a
function of both top and bottom MOSFET RDS(ON) and
the duty cycle (DC) as follows:
RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC)
TheRDS(ON)forboththetopandbottomMOSFETscanbe
obtained from the Typical Performance Characteristics
curves. So to calculate conduction losses:
Conduction Loss = IOUT2 (RSW + RL)
2. The internal LDO supplies the power to the INTVCC rail.
The total power loss here is the sum of the switching
losses and quiescent current losses from the control
circuitry.
Each time a power MOSFET gate is switched from low
to high to low again, a packet of charge dQ moves from
VIN to ground. The resulting dQ/dt is a current out of
INTVCC that is typically much larger than the DC control
bias current. In continuous mode, IGATECHG = f (QT +
QB),whereQTandQBarethegatechargesoftheinternal
top and bottom power MOSFETs and f is the switching
frequency. For estimation purposes, (QT + QB) on each
LTC3634 regulator channel is approximately 2.3nC.
To calculate the total power loss from the LDO load,
simply add the gate charge current and quiescent cur-
rent and multiply by VIN:
PLDO = (IGATECHG + IQ) VIN
3.Otherhiddenlossessuchastransitionloss,coppertrace
resistances, and internal load currents can account for
additional efficiency degradations in the overall power
system. Transition loss arises from the brief amount of
time the top power MOSFET spends in the saturated
region during switch node transitions. The LTC3634
internalpowerdevicesswitchquicklyenoughthatthese
losses are not significant compared to other sources.
Other losses, including diode conduction losses during
dead-time and inductor core losses, generally account
for less than 2% total additional loss.
Thermal Considerations
The LTC3634 requires the exposed package back-plane
metal (PGND) to be well soldered to the PC board to
provide good thermal contact. This gives the QFN and
TSSOP packages exceptional thermal properties, which
are necessary to prevent excessive self-heating of the part
in normal operation.
In a majority of applications, the LTC3634 does not dis-
sipate much heat due to its high efficiency and low thermal
resistance of its exposed-back QFN package. However, in
applications where the LTC3634 is running at high ambi-
ent temperature, high VIN, high switching frequency, and
maximum output current load, the heat dissipated may
exceed the maximum junction temperature of the part. If
the junction temperature reaches approximately 160°C,
bothpowerswitcheswillbeturnedoffuntilthetemperature
returns to 150°C.
To prevent the LTC3634 from exceeding the maximum
junction temperature of 125°C, 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 tempera-
ture rise is given by:
TRISE = PD θJA
applicaTions inForMaTion
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3634HFE#PBF | 制造商:Linear Technology 功能描述:IC CONV DDR DDR2 DDR3 28TSSOP 制造商:Linear Technology 功能描述:BUCK 15V 3A 500KHZ-4MHZ TS 制造商:Linear Technology 功能描述:DP-SWREG/Monolithic, 15V Dual 3A Monolithic Step Down Regulator for DDR Power 制造商:Linear Technology 功能描述:DC-DC REGULATOR, BUCK, ADJ, TSSOP-28, Primary Input Voltage:15V, No. of Outputs:2, Output Current:3A, No. of Pins:28, Operating Temperature Min:-40C, Operating Temperature Max:150C, MSL:MSL 1 - Unlimited, Package / Case:28-TSSOP , RoHS Compliant: Yes |
| LTC3634HFE#TRPBF | 制造商:Linear Technology 功能描述:IC REG 15V 3A STEP DOWN 28-TSSOP |
| LTC3634HUFD#PBF | 制造商:Linear Technology 功能描述:IC CONV DDR DDR2 DDR3 28-QFN 制造商:Linear Technology 功能描述:BUCK 15V 3A 500KHZ-4MHZ QF 制造商:Linear Technology 功能描述:DC-DC REGULATOR, BUCK, ADJ, QFN-28, Primary Input Voltage:15V, No. of Outputs:2, Output Current:3A, No. of Pins:28, Operating Temperature Min:-40C, Operating Temperature Max:150C, MSL:MSL 1 - Unlimited, Package / Case:28-QFN , RoHS Compliant: Yes |
| LTC3634HUFD#TRPBF | 制造商:Linear Technology 功能描述:IC REG 15V 3A STEP DOWN 28-QFN 制造商:Linear Technology 功能描述:DC-DC REGULATOR, BUCK, ADJ, QFN-28, Primary Input Voltage:15V, No. of Outputs:2, Output Current:3A, No. of Pins:28, Operating Temperature Min:-40C, Operating Temperature Max:150C, MSL:-, Package / Case:28-QFN , RoHS Compliant: Yes |
| LTC3634IFE#PBF | 功能描述:IC CONV DDR DDR2 DDR3 28TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:43 系列:- 应用:控制器，Intel VR11 输入电压:5 V ~ 12 V 输出数:1 输出电压:0.5 V ~ 1.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-VFQFN 裸露焊盘 供应商设备封装:48-QFN（7x7） 包装:管件 |
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