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| 型号： | LT1737IS#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 18/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO CM 16SOIC |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 125kHz |
| 占空比： | 90% |
| 电源电压： | 4.1 V ~ 20 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
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LT1737
APPLICATIO S I FOR ATIO
Output Impedance Error
An additional error source is caused by transformer sec-
ondary current flow through the real life nonzero imped-
ances of the output rectifier, transformer secondary and
output capacitor. Because the secondary current only
flows during the off portion of the duty cycle, the effective
output impedance equals the “DC” lumped secondary
impedance times the inverse of the off duty cycle. If the
output load current remains relatively constant, or, in less
critical applications, the error may be judged acceptable
and the feedback resistor divider ratio adjusted for nomi-
nal expected error. In more demanding applications, out-
put impedance error may be minimized by the use of the
load compensation function (see Load Compensation).
f = switching frequency
L PRI = transformer primary side inductance
V IN = input voltage
V OUT = output voltage
t ON = output switch minimum on time
An additional constraint has to do with the minimum
enable time. The LT1737 derives its output voltage infor-
mation from the flyback pulse. If the internal minimum
enable time pulse extends beyond the flyback pulse, loss
of regulation will occur. The onset of this condition can be
determined by setting the width of the flyback pulse equal
to the sum of the flyback enable delay, t ED , plus the
minimum enable time, t EN . Minimum power delivered to
the load is then:
[
(
1 ? f ?
? V OUT EN ED
?
) ]
MINIMUM LOAD CONSIDERATIONS
The LT1737 generally provides better low load perfor-
mance than previous generation switcher/controllers uti-
lizing indirect output voltage sensing techniques.
Specifically, it contains circuitry to detect flyback pulse
Minimum Power = ? t + t
2 ? L SEC ?
= V OUT ? I OUT
Which yields a minimum output constraint:
2
(
1 ? f ? V OUT ?
? t ED EN
?
)
“collapse,”therebysupportingoperationwellintodiscon-
tinuous mode. Nevertheless, there still remain constraints
to ultimate low load operation. These relate to the mini-
I OUT ( MIN ) =
2 ? L SEC ?
+ t
2
where
mum switch on time and the minimum enable time.
Discontinuous mode operation will be assumed in the
following theoretical derivations.
As outlined in the Operation section, the LT1737 utilizes a
minimum output switch on time, t ON . This value can be
combined with expected V IN and switching frequency to
yield an expression for minimum delivered power.
f = switching frequency
L SEC = transformer secondary side inductance
V OUT = output voltage
t ED = enable delay time
t EN = minimum enable time
Note that generally, depending on the particulars of input
(
1 ? f ?
? V IN ON
?
)
Minimum Power = ? t
2 ? L PRI ?
= V OUT ? I OUT
2
and output voltages and transformer inductance, one of
the above constraints will prove more restrictive. In other
words, the minimum load current in a particular applica-
tion will be either “output switch minimum on time”
This expression then yields a minimum output current
constraint:
constrained, or “minimum flyback pulse time” constrained.
(A final note—L PRI and L SEC refer to transformer induc-
(
? ? V IN ? t ON
)
I OUT ( MIN ) =
1 ? f ?
2 ? L PRI ? V OUT ?
2
where
tance as seen from the primary or secondary side respec-
tively. This general treatment allows these expressions to
be used when the transformer turns ratio is nonunity.)
1737fa
18
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| LT1738 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Slew Rate Controlled Ultralow Noise DC/DC Controller |
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| LT1738EG#PBF | 功能描述:IC REG CTRLR PWM CM 20-SSOP 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 |
| LT1738EG#TR | 功能描述:IC REG CTRLR PWM CM 20-SSOP 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:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 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:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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