原标题：ST EVL400W－EUPL7 400W开关电源解决方案

　　ST公司的EVL400W-EUPL7是基于L4984, L6699和SRK2001的12V/400W开关电源(SMPS)演示板.而L4984D电流模式PFC控制器和线路调制的固定关断时间(LM-FOT)控制.专用的LM-FOT调制器允许升压PFC转换器固定频率操作,只要是工作在连续导通模式(CCM).EVL400W-EUPL7演示板是12V 400W转换器,特别设计用于AC/DC适配器,具有宽输入火线电压范围,在轻负载时有非常低的功耗和良好的平均效率.演示板基于两级方案:基于CCM升压PFC控制器(采用L4984)的前端PFC预调节级和下行LLC谐振半桥转换器(采用L6699设计).在次级边,同步整流(SR)由SRK2001来实现,保证了有非常高的整流效率,因此仅需要小型的散热器.本文介绍了L4984D主要特性和框图,演示板EVL400W-EUPL7主要特性,电路图,以及演示板中的主板,控制板和整流板的材清单,PCB设计图.

　　The L4984D is a current-mode PFC controller operating with line-modulated fixed-off-time (LM-FOT) control. A proprietary LM-FOT modulator allows fixed-frequency operation for boost PFC converters as long as they are operated in CCM (continuous conduction mode).

　　The chip comes in a 10-pin SO package and offers a low-cost solution for CCM-operated boost PFC pre-regulators in EN61000-3-2 and JEIDA-MITI compliant applications, in a power range that spans from few hundred W to 1 KW and above.

　　The highly linear multiplier includes a special circuit, able to reduce the crossover distortion of the AC input current, that allows wide-range-mains operation with a reasonably low THD, even over a large load range.

　　The output voltage is controlled by means of a voltage-mode error amplifier and an accurate (1% at Tj = 25 C) internal voltage reference. Loop stability is optimized by the voltage feedforward function (1/V2correction), which in this IC uses a proprietary technique that also significantly improves line transient response in the case of mains drops and surges (“bi-directional”).

　　The device features low consumption and includes a disable function suitable for IC remote on/off. These features allow use in applications which also comply with the latest energy saving requirements (Blue Angel, ENERGY STAR, Energy 2000, etc.).

　　In addition to overvoltage protection able to keep the output voltage under control during transient conditions, the IC is also provided with protection against feedback loop failures or erroneous settings. Other onboard protection functions allow that brownout conditions and boost inductor saturation can be safely handled. Soft-start limits peak current and extends off-time to prevent flux runaway in the initial cycles.

　　The totem pole output stage, capable of 600 mA source and 800 mA sink current, is suitable for big MOSFETs or IGBT drive.

　　L4984D主要特性:

　　Line-modulated fixed-off-time (LM-FOT) control of CCM-operated PFC pre-regulators

　　Proprietary LM-FOT modulator for nearly fixed-frequency operation

　　Proprietary multiplier design for minimum THD of AC input current

　　Fast “bi-directional” input voltage feedforward (1/V2correction)

　　Accurate adjustable output overvoltage protection

　　Protection against feedback loop failure (latched shutdown)

　　Inductor saturation protection

　　AC brownout detection

　　Digital leading-edge blanking on current sense

　　Soft-start

　　1% (at Tj = 25 C) internal reference voltage

　　- 600 / + 800 mA totem pole gate driver with active pull-down during UVLO and voltage clamp

　　SSOP10 package

　　12 V - 400 W adapter based on L4984,L6699 and SRK2001

　　演示板EVL400W-EUPL7主要特性:

　　The EVL400W-EUPL7 demonstration board is a 12 V - 400 W converter, tailored for the typical specification of an AC/DC adapter with wide input mains range, very low power consumption at light load and good average efficiency.

　　The architecture is based on a two-stage approach: a front-end PFC pre-regulator based

　　on a CCM (continuous conduction mode) boost PFC controller using the L4984, and a

　　downstream LLC resonant half-bridge converter, designed around the L6699.

　　At the secondary side, synchronous rectification is implemented by means of the SRK2001 that assures a very high rectification efficiency with consequent small Heat Sink required.

　　The PFC section uses a proprietary LM-FOT (line-modulated fixed-off-time) that allows control methodology at fixed frequency operation for boost PFC converters as long as its operating in CCM.

　　The LLC section uses the L6699, a double-ended controller specific to series-resonant half-bridge topology. The output voltage regulation is obtained by modulating the operating frequency.

　　The main focus of this demonstration board is the light-load efficiency, achieved through the burst mode function of both PFC and LLC controllers with the self-adaptive deadtime of the L6699, modulated by the internal logic according to the half-bridge node transition times, which allows the maximization of the transformer magnetizing inductance, reducing the primary current at light load operation.

　　An active high voltage start-up circuitry based on a depletion MOSFET provides a very fast start-up time and minimizes the residual consumption during normal operation to a

　　negligible level.

　　图1. L4984D框图

　　图2.评估板EVL400W-EUPL7外形图