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参数资料
| 型号： | LT3845AEFE#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16 |
| 文件页数： | 8/26页 |
| 文件大小： | 284K |
| 代理商： | LT3845AEFE#PBF |
LT3845A
16
3845afa
APPLICATIONS INFORMATION
Note that RDS(ON) has a large positive temperature
dependence. The MOSFET manufacturer’s data sheet
contains a curve, RDS(ON) vs Temperature.
In the main MOSFET, transition losses are proportional
to VIN2 and can be considerably large in high voltage
applications(VIN>20V).Calculatethemaximumtransition
losses:
PTRAN(TOP) = k VIN2 IOUT(MAX) CRSS fSW
where k is a constant inversely related to the gate
driver current, approximated by k = 2 for LT3845A
applications.
The total maximum power dissipations of the MOSFET
are:
PTOP(TOTAL) = PCOND(MAIN) + PTRAN(MAIN)
PBOT(TOTAL) = PCOND(SYNC)
To achieve high supply efficiency, keep the total power
dissipation in each switch to less than 3% of the total
output power. Also, complete a thermal analysis to ensure
that the MOSFET junction temperature is not exceeded.
TJ = TA + P(TOTAL) qJA
where
qJA is the package thermal resistance and TA is the
ambient temperature. Keep the calculated TJ below the
maximum specified junction temperature, typically 150°C.
Note that when VIN is high and fSW is high, the transition
losses may dominate. A MOSFET with higher RDS(ON)
and lower CRSS may provide higher efficiency. MOSFETs
with higher voltage VDSS specification usually have higher
RDS(ON) and lower CRSS.
Choose the MOSFET VDSS specification to exceed the
maximum voltage across the drain to the source of the
MOSFET, which is VIN(MAX) plus any additional ringing
on the switch node. Ringing on the switch node can be
greatly reduced with good PCB layout and, if necessary,
an RC snubber.
In some applications, parasitic FET capacitances couple
the negative going switch node transient onto the bottom
gate drive pin of the LT3845A, causing a negative voltage
in excess of the Absolute Maximum Rating to be imposed
on that pin. Connection of a catch Schottky diode from
this pin to ground will eliminate this effect. A 1A current
rating is typically sufficient of the diode.
The internal VCC regulator is capable of sourcing up to
40mA limiting the maximum total MOSFET gate charge,
QG, to 35mA/fSW. The QG vs VGS specification is typically
provided in the MOSFET data sheet. Use QG at VGS of 8V.
If VCC is back driven from an external supply, the MOSFET
drive current is not sourced from the internal regulator
of the LT3845A and the QG of the MOSFET is not limited
by the IC. However, note that the MOSFET drive current
is supplied by the internal regulator when the external
supply back driving VCC is not available such as during
start-up or short circuit.
The manufacturer’s maximum continuous drain current
specification should exceed the peak switch current,
IOUT(MAX) + DIL/2.
During the supply start-up, the gate drive levels are set by
the VCC voltage regulator, which is approximately 8V. Once
the supply is up and running, the VCC can be back driven
by an auxiliary supply such as VOUT. It is important not
to exceed the manufacturer’s maximum VGS specification.
A standard level threshold MOSFET typically has a VGS
maximum of 20V.
Input Capacitor Selection
A local input bypass capacitor is required for buck
converters because the input current is pulsed with fast
riseandfalltimes.Theinputcapacitorselectioncriteriaare
based on the bulk capacitance and RMS current capability.
The bulk capacitance will determine the supply input ripple
voltage. The RMS current capability is used to prevent
overheating the capacitor.
The bulk capacitance is calculated based on maximum
input ripple,
DVIN:
CIN(BULK) =
IOUT(MAX) VOUT
DVIN fSW VIN(MIN)
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3845AIFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT3845AIFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT3845AMPFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT3845AMPFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT3845EFE | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Voltage Synchronous Current Mode Step-Down Controller with Adjustable Operating Frequency |
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