LTC3707-SYNC 데이터 시트보기 (PDF) - Linear Technology

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LTC3707-SYNC

High Efficiency, 2-Phase Synchronous Step-Down Switching Regulator

Linear Technology 

LTC3707-SYNC

U

OPERATIO (Refer to Functional Diagram)

5V SWITCH

20V/DIV

3.3V SWITCH

20V/DIV

INPUT CURRENT

5A/DIV

INPUT VOLTAGE

500mV/DIV

IIN(MEAS) = 2.53ARMS

(a)

3707 F03a

IIN(MEAS) = 1.55ARMS

(b)

3707 F03b

Figure 3. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for

Dual Switching Regulators Converting 12V to 5V and 3.3V at 3A Each. The Reduced Input

Ripple with the LTC1628 2-Phase Regulator Allows Less Expensive Input Capacitors,

Reduces Shielding Requirements for EMI and Improves Efficiency

Of course, the improvement afforded by 2-phase opera-

tion is a function of the dual switching regulator’s relative

duty cycles which, in turn, are dependent upon the input

voltage VIN (Duty Cycle = VOUT/VIN). Figure 4 shows how

the RMS input current varies for single-phase and 2-phase

operation for 3.3V and 5V regulators over a wide input

voltage range.

It can readily be seen that the advantages of 2-phase

operation are not just limited to a narrow operating range,

but in fact extend over a wide region. A good rule of thumb

for most applications is that 2-phase operation will reduce

the input capacitor requirement to that for just one channel

operating at maximum current and 50% duty cycle.

A final question: If 2-phase operation offers such an

advantage over single-phase operation for dual switching

regulators, why hasn’t it been done before? The answer is

that, while simple in concept, it is hard to implement.

Constant-frequency current mode switching regulators

require an oscillator derived “slope compensation” signal

to allow stable operation of each regulator at over 50%

duty cycle. This signal is relatively easy to derive in single-

phase dual switching regulators, but required the develop-

ment of a new and proprietary technique to allow 2-phase

operation. In addition, isolation between the two channels

becomes more critical with 2-phase operation because

switch transitions in one channel could potentially disrupt

the operation of the other channel.

The LTC1628 family of parts is proof that these hurdles

have been surmounted. The new device offers unique

advantages for the ever-expanding number of high effi-

ciency power supplies required in portable electronics.

3.0

SINGLE PHASE

2.5

DUAL CONTROLLER

2.0

1.5

2-PHASE

DUAL CONTROLLER

1.0

0.5

VO1 = 5V/3A

VO2 = 3.3V/3A

0

0

10

20

30

INPUT VOLTAGE (V)

40

3707 F04

Figure 4. RMS Input Current Comparison

3707sf

12

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