Linear公司的LTC7821是混合降壓同步電源轉(zhuǎn)換控制器，把軟開關(guān)電荷泵拓?fù)浜屯?a href="http://www.nxhydt.com/tags/降壓轉(zhuǎn)換器/" target="_blank">降壓轉(zhuǎn)換器組合起來，提供高達(dá)97%的效率和更好的EMI性能，VIN輸入電壓10V-72V，可鎖相固定頻率200kHz到1.5MHz，輸出電壓精度±1%，可編CCM，DCM或突發(fā)模式工作，主要用在中間總線轉(zhuǎn)換，大電流分布電源系統(tǒng)，通信，數(shù)據(jù)通信和存儲系統(tǒng)。本文介紹了LTC7821主要特性，框圖，應(yīng)用電路，以及演示板DC2513A主要指標(biāo)，測量建立圖，電路圖和材料清單。

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應(yīng)用：

Intermediate Bus Converters

High Current Distributed Power Systems

Telecom， Datacom， and Storage Systems

圖1.LTC7821框圖

圖2.LTC7821應(yīng)用電路圖（1）

圖3.LTC7821應(yīng)用電路圖（2）：500kHz，48V/9V，20A降壓轉(zhuǎn)換器

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主要指標(biāo)：

圖4.演示板DC2513A測量建立圖

圖5.演示板DC2513A電路圖

演示板DC2513A材料清單：