基于UCC29950 CCM PFC 和·LLC Combo 控制器

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基于UCC29950 CCM PFC 和·LLC Combo 控制器

　　1 特性

　　高效功率因数校正 (PFC) 和半桥谐振逻辑链路控制 (LLC) 组合控制器

　　连续导通模式 (CCM) 升压功率因数校正

　　支持自偏置或辅助(外部)偏置工作模式

　　完全内部补偿的 PFC 环路

　　3 步轻松设计 PFC 级

　　(设计电压反馈、电流反馈和功率级)

　　100kHz 固定 PFC 频率，具有抖动特性，可确保符合 EMI 标准

　　真正的输入功率限制，独立于线路电压

　　固定 LLC 频率工作范围为 70kHz 至 350kHz

　　死区变化范围为 LLC 半桥功率级的整个负载范围，可扩展零电压开关 (ZVS) 范围

　　三级 LLC 过流保护

　　Hiccup 工作模式，可提供连续过载和短路保护

　　低待机功耗，由高压启动金属氧化物半导体场效应晶体管 (MOSFET) 和 X-Cap 放电功能共同实现

　　内置软启动和转换器排序功能，可简化设计

　　交流线路欠压保护，具有故障指示器

　　PFC 总线过压和欠压保护

　　过温保护

　　用于扩展功率级的外部栅极驱动器

　　小外形尺寸集成电路 (SOIC)-16 封装

　　2 应用

　　离线交流-直流服务器电源(通过 80 PLUS® 铜牌/银牌/金牌认证)

　　工业 DIN 导轨和开放式电源

　　游戏机和打印机电源

　　高密度适配器

　　照明驱动器

　　3 说明

　　UCC29950 可为交流-直流转换器提供 LLC 转换器级和 CCM 升压功率因数校正 (PFC) 级，从而实现全部控制功能。 这款转换器经过了优化，非常便于使用。

　　凭借专有 CCM PFC 算法，系统能够获得高效率、更小的转换器尺寸以及高功率因数等诸多优势。 集成的 LLC 控制器可实现高效直流-直流转换级，利用软开关来降低电磁干扰 (EMI) 噪声。 这款组合控制器兼具 PFC 控制和 LLC 控制，使得控制算法能够充分利用来自两级的信息。

　　该控制器包含一个启动控制电路，此电路采用耗尽型 MOSFET 且内置器件电源管理功能，可最大程度降低外部元件需求，并且有助于降低系统实现成本。

　　为进一步降低待机功耗，该控制器还集成了 X-Cap 放电电路。 UCC29950 实现了一整套系统保护功能，其中包括交流线路欠压保护、PFC 总线欠压 PFC 和 LLC、过流保护和热关断保护。

　　The SUFG and SUFS are the control pins for an external start-up depletion mode FET. The use of a switched device here eliminates the static power dissipation in a conventional resistive start-up approach where a drop resistor from the rectified AC line to VCC is typically used. As a result standby power consumption is reduced.

　　Connect the FET gate to SUFG and its source to SUFS. The drain of the FET is connected to the rectified AC voltage. SUFG and SUFS control the initial charging of the capacitor on the VCC rail during start-up in the Self-Bias mode of operation. In this mode SUFG tracks SUFS as CVCC is charged and VCC rises. When VCC reaches VCCSB(start) (typically 16.2 V) SUFG goes low. This turns the start-up FET off and the PFC and LLC gate outputs start running. SUFG remains low unless VCC falls below VCCSB_UVLO(stop) (typically 7.9 V) or an X-Cap discharge is required. If VCC falls below VCCSB_UVLO(stop) then SUFG goes high to turn the start-up FET on and recharge CVCC back up to VCCSB_START.

　　SUFG and SUFS also provide an X-Cap discharge function in both Aux Bias and Self Bias Modes. This function is described fully in Active X-Cap Discharge.

　　If the UCC29950 is used in Aux Bias Mode then VCC is supplied by an external source and the external depletion mode FET is used only to provide the X-Cap discharge function. SUFG is at 0 V after a time TMODE_SEL_READ has elapsed during power up after CVCC exceeds VCCSTART. SUFG goes high whenever an X-Cap discharge is required. If the start up FET is not used and X-Cap discharge is not desired then SUFS should be connected to VCC and SUFG should be left open circuit.

　　The UCC29950 combines all the functions necessary to control a Boost PFC and LLC power system. It is packaged in an SOIC-16 package. The SUFG and SUFS pins allow the system designer to use an external depletion mode MOSFET to provide start up power instead of using a dissipative resistor. The use of high-impedance voltage sensing networks further reduces standby power. The combo device uses information from both PFC and LLC stages to optimize the system efficiency, transient response and standby power. The controller can be operated with bias current supplied from a small external PSU (Aux Bias) or from a winding on the LLC transformer (Self Bias). In Aux Bias Mode, the MD_SEL/PS_ON pin allows the user to turn on the PFC stage alone or both PFC and LLC stages.

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　　An LLC stage is typically used to convert the PFC stage output to an isolated final voltage for system use. The UCC29950 provides all the primary-side functions needed to control such a second stage. The input to the FB pin is an isolated control signal from the output. This signal is fed into a voltage-to-frequency converter (VCO). The VCO inserts an appropriate dead time and the resulting signals are routed through some on-chip drivers connected to the GD1 and GD2 outputs. The dead time is shortest at low LLC frequencies and is increased automatically as frequency is increased. A three level Over-Current Protection (OCP) function stops the GD1 and GD2 signals if the current signal at the LLC_CS pin goes outside of a defined current vs time profile.