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参数资料
| 型号： | LTC3788EGN-1#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-28 |
| 文件页数： | 8/30页 |
| 文件大小： | 384K |
| 代理商： | LTC3788EGN-1#TRPBF |
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LTC3788-1
16
37881fb
applicaTions inForMaTion
due to the extra switching losses incurred through R1.
However,DCRsensingeliminatesasenseresistor,reduces
conduction losses and provides higher efficiency at heavy
loads.Peakefficiencyisaboutthesamewitheithermethod.
Inductor Value Calculation
The operating frequency and inductor selection are inter-
relatedinthathigheroperatingfrequenciesallowtheuseof
smaller inductor and capacitor values. Why would anyone
ever choose to operate at lower frequencies with larger
components?Theanswerisefficiency.Ahigherfrequency
generally results in lower efficiency because of MOSFET
gate charge and switching losses. In addition to this basic
trade-off, the effect of inductor value on ripple current and
low current operation must also be considered.
The inductor value has a direct effect on ripple current.
The inductor ripple current IL decreases with higher
inductance or frequency and increases with higher VIN:
IL =
VIN
f L
1
VIN
VOUT
Accepting larger values of IL allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is IL = 0.3(IMAX). The maximum
IL occurs at VIN = 1/2 VOUT.
The inductor value also has secondary effects. The tran-
sition to Burst Mode operation begins when the average
inductor current required results in a peak current below
10% of the current limit determined by RSENSE. Lower
inductor values (higher IL) will cause this to occur at
lower load currents, which can cause a dip in efficiency in
the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to decrease.
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efficiency converters generally cannot
affordthecorelossfoundinlowcostpowderedironcores,
forcingtheuseofmoreexpensiveferriteormolypermalloy
cores. Actual core loss is independent of core size for a
fixedinductorvalue,butitisverydependentoninductance
selected. As inductance increases, core losses go down.
Unfortunately,becauseincreasedinductancerequiresmore
turns of wire, copper losses will increase.
Ferrite core inductors have very low core loss and are
preferred at high switching frequencies, so design goals
can concentrate on copper loss and preventing satura-
tion. Ferrite core material saturates “hard,” which means
that inductance collapses abruptly when the peak design
current is exceeded. This results in an abrupt increase in
inductor ripple current and consequent output voltage
ripple. Do not allow the core to saturate!
Power MOSFET Selection
Two external power MOSFETs must be selected for each
controller in the LTC3788-1: one N-channel MOSFET for
the bottom (main) switch, and one N-channel MOSFET
for the top (synchronous) switch.
The peak-to-peak gate drive levels are set by the INTVCC
voltage. This voltage is typically 5.2V during start-up
(see EXTVCC pin connection). Consequently, logic-level
threshold MOSFETs must be used in most applications.
The only exception is if low input voltage is expected (VIN
< 5V); then, sub-logic level threshold MOSFETs (VGS(TH)
< 3V) should be used. Pay close attention to the BVDSS
specification for the MOSFETs as well; many of the logic
level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFETs include the
on-resistance RDS(ON), Miller capacitance CMILLER, input
voltage and maximum output current. Miller capacitance,
CMILLER, can be approximated from the gate charge curve
usually provided on the MOSFET manufacturer’s data
sheet. CMILLER is equal to the increase in gate charge
along the horizontal axis while the curve is approximately
flat divided by the specified change in VDS. This result is
then multiplied by the ratio of the application applied VDS
to the gate charge curve specified VDS. When the IC is
operating in continuous mode, the duty cycles for the top
and bottom MOSFETs are given by:
Main SwitchDuty Cycle
=
VOUT VIN
VOUT
Synchronous SwitchDuty Cycle
=
VIN
VOUT
相关PDF资料 |
PDF描述 |
|---|---|
| LTC3789EGN#TRPBF | 0.1 A SWITCHING CONTROLLER, 710 kHz SWITCHING FREQ-MAX, PDSO28 |
| LTC3789EUFD#TRPBF | 0.1 A SWITCHING CONTROLLER, 710 kHz SWITCHING FREQ-MAX, PQCC28 |
| LTC3789EGN#PBF | 0.1 A SWITCHING CONTROLLER, 710 kHz SWITCHING FREQ-MAX, PDSO28 |
| LTC3789IUFD#PBF | 0.1 A SWITCHING CONTROLLER, 710 kHz SWITCHING FREQ-MAX, PQCC28 |
| LTC3789IGN#TRPBF | 0.1 A SWITCHING CONTROLLER, 710 kHz SWITCHING FREQ-MAX, PDSO28 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3788EUH#PBF | 功能描述:IC REG CTRLR BST PWM CM 32-QFN 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 |
| LTC3788EUH#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 32-QFN 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 |
| LTC3788IGN-1#PBF | 功能描述:IC REG CTRLR BST PWM CM 28-SSOP 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 |
| LTC3788IGN-1#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 28-SSOP 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 |
| LTC3788IUH#PBF | 功能描述:IC REG CTRLR BST PWM CM 32-QFN 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 |
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