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参数资料
| 型号： | MAX5975AETE+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 12/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO CM 16TQFN |
| 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： | 84% |
| 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 ~ 85°C |
| 封装/外壳： | 16-WFQFN 裸露焊盘 |
| 包装： | 管件 |
Current-Mode PWM Controllers with Frequency
Dithering for EMI-Sensitive Power Supplies
V EN(MAX)
Detailed Description
The MAX5975_ is optimized for controlling a 25W to
50W forward/flyback converter in continuous-conduction
mode. The power MOSFET gate driver (NDRV) is sized
to optimize efficiency for 25W design. The feature-rich
devices are ideal for PoE IEEE 802.3af/at-powered
devices.
The MAX5975A offers a bootstrap UVLO wakeup level of
20V with a wide hysteresis of 13V. The low startup and
operating currents allow the use of a smaller storage
capacitor at the input without compromising startup and
hold times. The device is well-suited for universal input
(rectified 85V AC to 265V AC) or telecom (-36V DC to
-72V DC) power supplies.
The MAX5975B has a UVLO rising threshold of 10V and
is well-suited for low-input voltage (12V DC to 24V DC)
power sources such as wall adapters.
Power supplies designed with the MAX5975A use a
high-value startup resistor, R IN , that charges a reservoir
capacitor, C IN (see the Typical Applications Circuits ).
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
changes 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 driver whenever the internally set threshold
of 400mV is exceeded. Eight consecutive occurrences
of current-limit event trigger hiccup mode, which pro-
tects external components by halting switching for a
period of time (t RSTRT ) and allowing the overload current
to dissipate in the load and body diode of the synchro-
nous rectifier before soft-start is reattempted.
12
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.
Secondly, 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.
Enable Input
The enable input EN is used to enable or disable the
device. Connect EN to IN for always enabled applica-
tions. Connecting EN to ground disables the device and
reduces current consumption to 100 F A.
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 PGND is required to prevent
IN from exceeding its absolute maximum rating of 26V
when the device is disabled. The zener diode should
be inactive below the maximum UVLO rising threshold
voltage V INUVR(MAX) (21V for the MAX5975A and 10.5V
for the MAX5975B). Design the resistive divider by first
selecting the value of R EN1 to be on the order of 100k I .
Then calculate R EN2 as follows:
R EN2 = R EN1
V S(UVLO) ? V EN(MAX)
where V EN(MAX) is the maximum enable threshold volt-
age and is equal to 1.26V and V S(UVLO) is the desired
UVLO threshold for the power source, below which the
devices are disabled.
In the case where EN is externally controlled and UVLO for
the power source is unnecessary, connect EN to IN and an
open-drain or open-collector output as shown in Figure 2.
The digital output connected to EN should be capable of
withstanding IN’s absolute maximum voltage of 26V.
Bootstrap Undervoltage Lockout
The device has an internal bootstrap UVLO that is very
useful when designing high-voltage power supplies (see
the Block Diagram ). This allows the device to bootstrap
itself during initial power-up. The MAX5975A soft-starts
when V IN exceeds the bootstrap UVLO threshold of
V INUVR (20V typ).
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX5975AETE+ | 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 |
| MAX5975AETE+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 |
| MAX5975BETE+ | 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 |
| MAX5975BETE+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 |
| MAX5975CETE+ | 制造商:Maxim Integrated Products 功能描述:CURRENT-MODE PWM CONTROLLERS WITH FREQUENCY DITHERING FOR EM - Rail/Tube |
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