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| 型号： | LT1339CSW#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM CM 20-SOIC |
| 标准包装： | 1,000 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 150kHz |
| 占空比： | 90% |
| 电源电压： | 最高 60V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 20-SOIC（0.295"，7.50mm 宽） |
| 包装： | 带卷 (TR) |
LT1339
APPLICATIO N S I N FOR M ATIO N
the converter input supply is enabled with no voltage on
the LT1339 12V IN pin, the LT1339 driver output clamps
will not be activated. To prevent turn-on, an external
current path must be used to bleed off charge on the
switch MOSFET gates. High value bleed resistors (50k to
250k) should be connected between the TG and SW pins
and between BG and PGND. This provides discharge paths
for the switch MOSFET gates, preventing parasitic turn-on
and damage to the MOSFETs.
Inductor Selection
Oscillator Synchronization
The LT1339 oscillator generates a modified sawtooth
waveform at the C T pin between low and high thresholds
of about 0.8V (vl) and 2.5V (vh) respectively. The oscillator
can be synchronized by driving a TTL level pulse into the
SYNC pin. This inputs to a one-shot circuit that reduces the
oscillator high threshold to 2V for about 200ns. The SYNC
input signal should have minimum high/low times of ≥ 1 μ s.
SYNC
The inductor for an LT1339 converter is selected based on
output power, operating frequency and efficiency require-
ments. Generally, the selection of inductor value can be
2.5V
2V
(vh)
reduced to desired maximum ripple current in the inductor
( ? I). For a buck converter, the minimum inductor value for
a desired maximum operating ripple current can be deter-
0.8V
FREE RUN
SYNCHRONIZED
V CT
(vl)
( V OUT ) ( V IN ? V OUT )
( )( I ? f O )( V IN )
mined using the following relation:
L MIN =
Figure 4. Free Run and Synchronized Oscillator
Waveforms (at C T Pin)
Slope Compensation
1339 F04
( V OUT ) ( V IN ? V OUT )
( )( )( L f O )( V IN )
where f O = operating frequency. Given an inductor value
(L), the peak inductor current is the sum of the average
inductor current (I AVG )and half the inductor ripple current
( ? I), or:
I PK = I AVG +
2
The inductor core type is determined by peak current and
efficiency requirements. The inductor core must with-
stand peak current without saturating, and series winding
resistance and core losses should be kept as small as is
practical to maximize conversion efficiency.
The LT1339 peak current limit threshold is 40% greater than
the average current limit threshold. Slope compensation
effects reduce this margin as duty cycle increases. This
margin must be maintained to prevent peak current limit
from corrupting the programmed value for average current
limit. Programming the peak ripple current to less than 15%
of the desired average current limit value will assure porper
operation of the average current limit feature through 90%
duty cycle (see Slope Compensation section).
12
Current mode switching regulators that operate with a
duty cycle greater than 50% and have continuous inductor
current can exhibit duty cycle instability. While a regulator
will not be damaged and may even continue to function
acceptably during this type of subharmonic oscillation, an
irritating high-pitched squeal is usually produced.
The criterion for current mode duty cycle instability is met
when the increasing slope of the inductor ripple current is
less than the decreasing slope, which is the case at duty
cycles greater than 50%. This condition is illustrated in
Figure 5a. The inductor ripple current starts at I 1 , at the
beginning of each oscillator switch cycle. Current
increases at a rate S1 until the current reaches the control
trip level I 2 . The controller servo loop then disables the
main switch (and enables the synchronous switch) and
inductor current begins to decrease at a rate S2. If the
current switch point (I 2 ) is perturbed slightly and
increased by ? I, the cycle time ends such that the mini-
mum current point is increased by a factor of (1 + S2/S1)
to start the next cycle. On each successive cycle, this error
is multiplied by a factor of S2/S1. Therefore, if S2/S1 is
≥ 1, the system is unstable.
sn1339 1339fas
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1339I | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Power Synchronous DC/DC Controller |
| LT1339IN | 功能描述:IC REG CTRLR BST PWM CM 20-DIP RoHS:否 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 |
| LT1339IN#PBF | 功能描述:IC REG CTRLR BST PWM CM 20-DIP 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 |
| LT1339ISW | 功能描述:IC REG CTRLR BST PWM CM 20-SOIC RoHS:否 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 |
| LT1339ISW#PBF | 功能描述:IC REG CTRLR BST PWM CM 20-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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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