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| 型号： | MAX5974EETE+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 14/22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
Detailed Description
The MAX5974_ are optimized for controlling a 25W
to 50W synchronous rectification flyback converter in
continuous-conduction mode. The main switch gate
driver (NDRV) and the output synchronous rectifier
driver (AUXDRV) are sized to optimize efficiency for 25W
design. The features-rich devices are ideal for PoE IEEE
802.3af/at-powered devices.
The MAX5974E offers a 16V bootstrap UVLO wake-up
level with a 9V wide hysteresis. The low startup and
operating currents allow the use of a smaller storage
capacitor at the input without compromising startup and
hold times. The MAX5974E is well-suited for universal
input (rectified 85V AC to 265V AC) or telecom (-36V DC
to -72V DC) power supplies.
The MAX5974F has a UVLO rising threshold of 8.4V and
can accommodate for low-input voltage (12V DC to 24V
DC) power sources such as wall adapters.
Power supplies designed with the MAX5974E use a
high-value startup resistor, R IN , that charges a reservoir
capacitor, C IN (see the Typical Application Circuit ).
During this initial period, while the voltage is less than
the internal bootstrap UVLO threshold, the device typi-
cally consumes only 100 F A of quiescent current. This
low startup current and the large bootstrap UVLO hys-
teresis help to minimize the power dissipation across R IN
even at the high end of the universal AC input voltage
(265V AC).
Feed-forward maximum duty-cycle clamping detects chang-
es in line conditions and adjusts the maximum duty cycle
accordingly to eliminate the clamp voltage’s (i.e., the main
power FET’s drain voltage) dependence on the input voltage.
For EMI-sensitive applications, the programmable fre-
quency dithering feature allows up to Q 10% variation in
the switching frequency. This spread-spectrum modula-
tion technique spreads the energy of switching harmon-
ics over a wider band while reducing their peaks, help-
ing to meet stringent EMI goals.
The devices include a cycle-by-cycle current limit
that turns off the main and AUX drivers whenever the
internally set threshold of 400mV is exceeded. Eight
consecutive occurrences of current-limit events trigger
hiccup mode, which protects external components by
halting switching for a period of time (t RSTRT ) and allow-
ing the overload current to dissipate in the load and
14
body diode of the synchronous rectifier before soft-start
is reattempted.
Current-Mode Control Loop
The advantages of current-mode control over voltage-
mode control are twofold. First, there is the feed-forward
characteristic brought on by the controller’s ability to adjust
for variations in the input voltage on a cycle-by-cycle basis.
Second, the stability requirements of the current-mode
controller are reduced to that of a single-pole system,
unlike the double pole in voltage-mode control.
The devices use a current-mode control loop where the
scaled output of the error amplifier (COMP) is compared
to a slope-compensated current-sense signal at CSSC.
Input Clamp
When the device is enabled, an internal 18V input clamp
is active. During an overvoltage condition, the clamp
prevents the voltage at the supply input IN from rising
above 18.5V (typ).
When the device is disabled, the input clamp circuitry is
also disabled.
Enable Input
The enable input is used to enable or disable the device.
Driving EN low disables the device. Note that the inter-
nal 18V input clamp is also disabled when EN is low.
Therefore, an external 18V zener diode is needed for
certain operating conditions as described in the follow-
ing sections.
UVLO on Power Source
The enable input has an accurate threshold of 1.26V
(max). For applications that require a UVLO on the-
power source, connect a resistive divider from the power
source to EN to GND as shown in Figure 1. A zener
diode between IN and GND is required to prevent the
NDRV and AUXDRV gate-drive voltages from exceeding
20V, the maximum allowed gate voltage of power FETs.
The external zener diode should clamp in the following
range:
20V > V Z > V UVLO(MAX)
where V Z is the zener voltage and V UVLO(MAX) is the
maximum wakeup level (16.5V or 8.85V depending
on the device version). A 18V zener diode is the best
choice.
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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