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参数资料
| 型号： | MAX5974EETE+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 20/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBACK PWM 16-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 1 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 占空比： | 82% |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 16-WFQFN 裸露焊盘 |
| 包装： | 管件 |
MAX5974E/MAX5974F
Current-Mode PWM Controllers for
Low-Cost Flyback Supplies
= V OUT ×
C IN = IN G SS
Applications Information
Startup Time Considerations
The bypass capacitor at IN, C IN , supplies current
immediately after the devices wake up (see the Typical
Application Circuit ). Large values of C IN increase the
startup time, but also supply gate charge for more
cycles during initial startup. If the value of C IN is too
small, V IN drops below 7V because NDRV does not have
enough time to switch and build up sufficient voltage
across the tertiary output, which powers the device. The
device goes back into UVLO and does not start. Use a
low-leakage capacitor for C IN .
Typically, offline power supplies keep startup times to
less than 500ms even in low-line conditions (85V AC
input for universal offline or 36V DC for telecom applica-
tions). Size the startup resistor, R IN , to supply both the
maximum startup bias of the device (150 F A) and the
charging current for C IN . C IN must be charged to 16V
within the desired 500ms time period. C IN must store
enough charge to deliver current to the device for at
least the soft-start time (t SS ) set by C SS . To calculate the
approximate amount of capacitance required, use the
following formula:
I G = Q GTOT f SW
(I + I )(t )
V HYST
where I IN is the ICs’ internal supply current (1.8mA)
after startup, Q GTOT is the total gate charge for the
n-channel and p-channel FETs, f SW is the ICs’ switch-
ing frequency, V HYST is the bootstrap UVLO hysteresis
(9V typ), and t SS is the soft-start time. R IN is then cal-
culated as follows:
where V S(MIN) is the minimum input supply voltage for
the application (36V for telecom), V INUVR is the boot-
strap UVLO wake-up level (16V), and I START is the IN
supply current at startup (150 F A max).
Choose a higher value for R IN than the one calculated
above if a longer startup time can be tolerated in order
to minimize power loss on this resistor.
Bias Circuit
An out-of-phase tertiary winding is needed to power the
bias circuit. The voltage across the tertiary V T during the
off-time is:
V
where V OUT is the output voltage and N T /N S is the turns
ratio from the tertiary to the secondary winding. Select the
turns ratio so that V T is above the UVLO shutdown level
(7.35V max) by a margin determined by the holdup time
needed to “ride through” a brownout.
Layout Recommendations
Typically, there are two sources of noise emission in a
switching power supply: high di/dt loops and high dV/dt
surfaces. For example, traces that carry the drain current
often form high di/dt loops. Similarly, the heatsink of the
main MOSFET presents a dV/dt source; therefore, mini-
mize the surface area of the MOSFET heatsink as much
as possible. Keep all PCB traces carrying switching cur-
rents as short as possible to minimize current loops. Use
a ground plane for best results.
For universal AC input design, follow all applicable
safety regulations. Offline power supplies can require
UL, VDE, and other similar agency approvals.
Refer to the MAX5974E Evaluation Kit data sheet for a
20
R IN ?
V S(MIN) ? V INUVR
I START
recommended layout and component values.
Maxim Integrated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX5974EETE+ | 功能描述:电流型 PWM 控制器 Current-Mode PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX5974EETE+T | 功能描述:电流型 PWM 控制器 Current-Mode PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX5974EEVKIT# | 功能描述:电流型 PWM 控制器 MAX5974E Eval Kit RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX5974FETE+ | 功能描述:电流型 PWM 控制器 Current-Mode PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX5974FETE+T | 功能描述:电流型 PWM 控制器 Current-Mode PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
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