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参数资料
| 型号： | LT3574EMS#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/24页 |
| 文件大小： | 0K |
| 描述： | IC REG FLYBK ISO ADJ .65A 16MSOP |
| 标准包装： | 2,500 |
| 类型： | 回扫，隔离 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 60V |
| 输入电压： | 3 V ~ 40 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 40kHz ~ 1MHz |
| 电流 - 输出： | 650mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TFSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-MSOP |
| 相关产品： | 732-2669-2-ND - TRANS FLYBACK LT3748 20UH SMD 732-2669-6-ND - TRANS FLYBACK LT3748 20UH SMD 732-2668-6-ND - TRANS FLYBACK LT3748 14UH SMD 732-2667-6-ND - TRANS FLYBACK LT3748 500UH SMD 732-2666-6-ND - TRANS FLYBACK LT3748 12UH SMD 732-2665-6-ND - TRANS FLYBACK LT3748 12UH SMD 732-2664-6-ND - TRANS FLYBACK LT3748 15UH SMD 732-2663-6-ND - TRANS FLYBACK LT3748 15UH SMD 732-2662-6-ND - TRANS FLYBACK LT3748 8UH SMD 732-2661-6-ND - TRANS FLYBACK LT3748 8UH SMD 更多... |
LT3574
APPLICATIONS INFORMATION
? ? V F ? I SEC ( ES R )
V OUT = V BG ?
A ? FLBK ? =
? V ? V BG
= V BG ?
? R FB ? ? 1 ?
? R REF ? ? ? ? A ? ?
= ? FB ? ?
D V F R 1 D V TC
? R FB 1 D V TC R FB
D V F / D T
D T
? ? V F
? R FB ? ? 1 ?
V OUT BG ?
? ? ? N
? R REF PS A ?
? ? TC ? ? – I SEC ( ESR )
ERRORAMPLIFIER—PSEUDODCTHEORY
In the Block Diagram, the R REF (R4) and R FB (R3) resistors
can be found. They are external resistors used to program
the output voltage. The LT3574 operates much the same way
as traditional current mode switchers, the major difference
being a different type of error amplifier which derives its
feedback information from the flyback pulse.
Operation is as follows: when the output switch, Q1, turns
off, its collector voltage rises above the V IN rail. The am-
plitude of this flyback pulse, i.e., the difference between
it and V IN , is given as:
V FLBK = (V OUT + V F + I SEC ? ESR) ? N PS
V F = D1 forward voltage
I SEC = Transformer secondary current
ESR = Total impedance of secondary circuit
N PS = Transformer effective primary-to-secondary
turns ratio
The flyback voltage is then converted to a current by
the action of R FB and Q2. Nearly all of this current flows
through resistor R REF to form a ground-referred voltage.
This voltage is fed into the flyback error amplifier. The
flyback error amplifier samples this output voltage infor-
mation when the secondary side winding current is zero.
The error amplifier uses a bandgap voltage, 1.23V, as the
reference voltage.
The relatively high gain in the overall loop will then cause
the voltage at the R REF resistor to be nearly equal to the
bandgap reference voltage V BG . The relationship between
V FLBK and V BG may then be expressed as:
or ,
? R FB ? R REF
V FLBK
A = Ratio of Q1 I C to I E , typically ≈ 0.986
V BG = Internal bandgap reference
In combination with the previous V FLBK expression yields
an expression for V OUT , in terms of the internal reference,
programming resistors, transformer turns ratio and diode
forward voltage drop:
? R FB ? ? 1 ?
? ?
? R REF ? ? A N PS ?
Additionally, it includes the effect of nonzero secondary
output impedance (ESR). This term can be assumed to
be zero in boundary control mode. More details will be
discussed in the next section.
Temperature Compensation
The first term in the V OUT equation does not have a tem-
perature dependence, but the diode forward drop has a
significant negative temperature coefficient. To compen-
sate for this, a positive temperature coefficient current
source is connected to the R REF pin. The current is set by
a resistor to ground connected to the T C pin. To cancel the
temperature coefficient, the following equation is used:
or ,
D T R TC N PS D T
R TC = ? ? ≈
N PS N PS
( D V F / D T ) = Diode’s forward voltage temperature
coefficient
( D V TC / D T) = 2mV
V TC = 0.55V
The resistor value given by this equation should also be
verified experimentally, and adjusted if necessary to achieve
optimal regulation over temperature.
The revised output voltage is as follows:
= V
?
? V ? R FB
? R TC ? N PS A
3574f
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3574IMS | 制造商:LINER 制造商全称:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
| LT3574IMS#PBF | 功能描述:IC REG FLYBK ISO ADJ .65A 16MSOP 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 |
| LT3574IMS#TRPBF | 功能描述:IC REG FLYBK ISO ADJ .65A 16MSOP 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 |
| LT3574IMSPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
| LT3574IMSTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
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