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参数资料
| 型号： | LTC3852IUDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR DOUBLER PWM 24-QFN |
| 标准包装： | 73 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 810kHz |
| 占空比： | 99% |
| 电源电压： | 2.7 V ~ 38 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 是 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3852
APPLICATIONS INFORMATION
V IN2
INTV CC
BOOST
TG
V IN
INDUCTOR
Accepting larger values of D I L 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 D I L = 0.3(I MAX ). The maximum
D I L occurs at the maximum input voltage.
LTC3852
SW
L
DCR
V OUT
The inductor value also has secondary effects. The tran-
BG
sition to Burst Mode operation begins when the average
GND2
SENSE +
SENSE –
C1*
R1**
R2
inductor current required results in a peak current below
≈10% of the current limit determined by R SENSE . Lower
inductor values (higher D I L ) will cause this to occur at
lower load currents, which can cause a dip in ef?ciency in
R1||R2 ? C1 =
*PLACE C1 NEAR SENSE + , SENSE – PINS
**PLACE R1 NEAR INDUCTOR
L
DCR
R SENSE(EQ) = DCR
R2
R1 + R2
3852 F03
the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to increase.
Figure 3. Current Mode Control Using the Inductor DCR
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant
frequency architectures by preventing sub-harmonic
oscillations at high duty cycles. It is accomplished internally
by adding a compensating ramp to the inductor current
signal. Normally, this results in a reduction of maximum
inductor peak current for duty cycles >40%. However, the
LTC3852 uses a novel scheme that allows the maximum
inductor peak current to remain unaffected throughout
all duty cycles.
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use of
smaller inductor and capacitor values. A higher frequency
generally results in lower ef?ciency because of MOSFET
gate charge 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 D I L decreases with higher
inductance or frequency and increases with higher V IN :
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High ef?ciency converters generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of more expensive ferrite or molypermalloy
cores. Actual core loss is independent of core size for a
?xed inductor value, but it is very dependent on inductance
selected. As inductance increases, core losses go down.
Unfortunately, increased inductance requires more turns
of wire and therefore copper losses will increase.
Ferrite designs have very low core loss and are preferred
at high switching frequencies, so design goals can con-
centrate on copper loss and preventing saturation. Ferrite
core material saturates “hard,” which means that induc-
tance 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 and Schottky Diode (Optional)
Selection
Two external power MOSFETs must be selected for the
LTC3852 controller: one N-channel MOSFET for the top
(main) switch, and one N-channel MOSFET for the bottom
V OUT ? 1 – OUT ?
ΔI L =
1
f ?L
? V ?
? V IN ?
(synchronous) switch.
3852f
16
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| LTC3853EUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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