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| 型号： | LT1425CS#TR |
| 厂商： | Linear Technology |
| 文件页数： | 15/20页 |
| 文件大小： | 0K |
| 描述： | IC REG FLYBK ISOLATED .2A 16SOIC |
| 标准包装： | 2,500 |
| 类型： | 回扫，隔离 |
| 输出数： | 1 |
| 输入电压： | 2.8 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 285kHz |
| 电流 - 输出： | 200mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-SOIC |
LT1425
) ) ) )
(t ED + t EN ) 2
L SEC
I OUT(MIN) =
APPLICATIO NS INFORMATION
1 f(V OUT )
2
where,
f = Switching frequency (nominally 285kHz)
L SEC = Transformer secondary side inductance
V OUT = Output voltage
t ED = Enable delay time
minimum switch ON time, irrespective of current trip
point. If the duty cycle exhibited by this minimum ON time
is greater than the ratio of secondary winding voltage
(referred-to-primary) divided by input voltage, then peak
current will not be controlled at the nominal value, and will
cycle-by-cycle ratchet up to some higher level. Expressed
mathematically, the requirement to maintain short-circuit
control is:
)
t EN = Minimum enable time
Note that generally, depending on the particulars of input
and output voltages and transformer inductance, one of
(t ON )(f) <
)
V F + (I SC )(R SEC )
(V IN )(N SP )
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”
constrained, or “minimum flyback pulse time” constrained.
(A final note —L PRI and L SEC refer to transformer induc-
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.)
MAXIMUM LOAD/SHORT-CIRCUIT CONSIDERATIONS
The LT1425 is a current mode controller. It uses the V C
node voltage as an input to a current comparator which
turns off the output switch on a cycle-by-cycle basis as
this peak current is reached. The internal clamp on the V C
node, nominally 1.9V, then acts as an output switch peak
current limit. This action becomes the switch current limit
specification. The maximum available output power is
then determined by the switch current limit, which is
somewhat duty cycle dependent due to internal slope
compensation action.
Short-circuit conditions are handled by the same mecha-
nism. The output switch turns on, peak current is quickly
reached and the switch is turned off. Because the output
switch is only on for a small fraction of the available period,
internal power dissipation is controlled. (The LT1425
contains an internal overtemperature shutdown circuit,
that disables switch action, just in case.)
While the majority of users will not experience a problem,
there is however, a possibility of loss of current limit under
where,
t ON = Output switch minimum ON time
f = Switching frequency
I SC = Short-circuit output current
V F = Output diode forward voltage at I SC
R SEC = Resistance of transformer secondary
V IN = Input voltage
N SP = Secondary-to-primary turns ratio
(N SEC /N PRI )
Trouble will typically only be encountered in applications
with a relatively high product of input voltage times
secondary-to-primary turns ratio. Additionally, several
real world effects such as transformer leakage inductance,
AC winding losses and output switch voltage drop com-
bine to make this simple theoretical calculation a conser-
vative estimate. In cases where short-circuit protection is
mandatory and this theoretical calculation indicates cause
for concern, the prototype should be observed directly as
follows: short the output while observing the V SW signal
with an oscilloscope. The measured output switch ON
time can then be compared against the specifications for
minimum t ON .
THERMAL CONSIDERATIONS
Care should be taken to ensure that the worst-case input
voltage and load current conditions do not cause exces-
sive die temperatures. The narrow 16-pin package is rated
at 75 ° C/W.
certain conditions. Remember that the LT1425 exhibits a
15
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| LT1425IS | 功能描述:IC REG FLYBK ISOLATED .2A 16SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1425IS#PBF | 功能描述:IC REG FLYBK ISOLATED .2A 16SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:MIC23xxx HyperLight Load™ Regulators 标准包装:5,000 系列:HyperLight Load® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.8V 输入电压:2.7 V ~ 5.5 V PWM 型:混合物 频率 - 开关:4MHz 电流 - 输出:2A 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘，8-MLF? 包装:带卷 (TR) 供应商设备封装:8-MLF?（2x2） 产品目录页面:1094 (CN2011-ZH PDF) 其它名称:576-3303-2 |
| LT1425IS#TR | 功能描述:IC REG FLYBK ISOLATED .2A 16SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1425IS#TRPBF | 功能描述:IC REG FLYBK ISOLATED .2A 16SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1425ISPBF | 制造商:Linear Technology 功能描述:Sw. Regulator Isolated Flyback SOIC16 |
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