LTC1628CG-SYNC Ver la hoja de datos (PDF) - Linear Technology

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LTC1628CG-SYNC

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

Linear Technology 

LTC1628-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)

DC236 F03a

IIN(MEAS) = 1.55ARMS

(b)

DC236 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-SYNC 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-SYNC is proof that these hurdles have been

surmounted. The new device offers unique advantages for

the ever-expanding number of high efficiency power sup-

plies 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

1628 F04

Figure 4. RMS Input Current Comparison

12

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