Linear公司的LTC7821是混合降压同步电源转换控制器,把软开关电荷泵拓扑和同步降压转换器组合起来,提供高达97%的效率和更好的EMI性能,VIN输入电压10V-72V,可锁相固定频率200kHz到1.5MHz,输出电压精度±1%,可编CCM,DCM或突发模式工作,主要用在中间总线转换,大电流分布电源系统,通信,数据通信和存储系统.本文介绍了LTC7821主要特性,框图,应用电路,以及演示板DC2513A主要指标,测量建立图,电路图和材料清单.

The LTC®7821 uses a proprietary architecture that mergesa soft switching charge pump topology with a synchronousstep-down converter to provide superior efficiencyand EMI performance compared to traditional switchingarchitectures.

In a typical 48V to 12V application, efficiency of greaterthan 97% is attainable with the LTC7821 switching at500kHz. The same efficiency can only be achieved with atraditional controller switching at one-third the frequency.

Higher switching frequencies allow the use of smaller inductancesthat yield faster transient response and smallersolution size.

The LTC7821 can be easily paralleled to provide higheroutput currents with its accurate current sharing capabilityand frequency synchronization function.

LTC7821主要特性:

Wide VIN Range: 10V to 72V (80V ABS Max)

Soft Switching for Low Noise Operation

Phase-Lockable Fixed Frequency 200kHz to 1.5MHz

±1% Output Voltage Accuracy

RSENSE or DCR Current Sensing

Programmable CCM, DCM, or Burst Mode® Operation

CLKOUT Pin for Multiphase Operation

Short Circuit Protected

EXTVCC Input for Improved Efficiency

Monotonic Output Voltage Start-Up

Optional External Reference

32-Pin (5mm × 5mm) QFN

LTC7821应用:

Intermediate Bus Converters

High Current Distributed Power Systems

Telecom, Datacom, and Storage Systems

图1.LTC7821框图

图2.LTC7821应用电路图(1)

图3.LTC7821应用电路图(2):500kHz,48V/9V,20A降压转换器

演示板DC2513A

Demonstration circuit 2513A is a high efficiency, highpower density hybrid converter. It can deliver 12V/20Awith an input voltage from 36V to 72V. This demo boardfeatures the LTC®7821, which uses an architecture thatmerges soft-switching switched-capacitor topology witha traditional step-down converter to provide superiorefficiency compared to the traditional switching architectures.

It offers a high efficiency/high density and costeffective solution for nonisolated intermediate bus applicationsin power distribution, datacom and telecom aswell as emerging 48V automotive systems.

External MOSFETs switch at a 500kHz fixed frequency forthis demo board and can be programmed from 200kHz to1.5MHz. The LTC7821’s powerful 1Ω N-channel MOSFET gate drivers maximize efficiency and can drive multipleMOSFETs in parallel for higher power applications. Due toits current mode control architecture, multiple LTC7821scan be operated in a parallel, multiphase configurationwith excellent current sharing and low output voltageripple to enable much higher power applications. Otherbenefits include low EMI emissions due to a soft-switchedfront end and reduced MOSFET stress.

The LTC7821 design eliminates the inrush current typicallyassociated with switched capacitor circuits by prebalancingthe capacitors on start-up. The LTC7821 alsomonitors system voltage, current and temperature forfaults, and uses a sense resistor for overcurrent protection.

It stops switching and pulls the FAULT pin low whena fault condition occurs. An onboard timer can be set forappropriate restart/retry times.

Additional features include ±1% output voltage accuracyover temperature, a clock output for multiphase operation,a power good output signal, short-circuit protection,monotonic output voltage start-up, optional external reference,undervoltage lockout and internal charge balancecircuitry.

The LTC7821 data sheet must be used in conjunction withthis demo board manual.

演示板DC2513A主要指标:

图4.演示板DC2513A测量建立图

图5.演示板DC2513A电路图

演示板DC2513A材料清单: