LTC3835 datasheet(14/40 Pages) LINER

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LTC3890-3

38903f

For more information www.linear.com/3890-3

operaTion (Refer to the Functional Diagram)

Figure 1. 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 2-Phase Regulator Allows

Less Expensive Input Capacitors, Reduces Shielding Requirements for EMI and Improves Efficiency

Figure 2. RMS Input Current Comparison

Figure1comparestheinputwaveformsforarepresentative

single-phase dual switching regulator to the LTC3890-3

2-phase dual switching regulator. An actual measure-

ment of the RMS input current under these conditions

shows that 2-phase operation dropped the input current

from 2.53ARMS to 1.55ARMS. While this is an impressive

reduction in itself, remember that the power losses are

proportionaltoIRMS2,meaningthattheactualpowerwasted

is reduced by a factor of 2.66. The reduced input ripple

voltage also means less power is lost in the input power

path, which could include batteries, switches, trace/con-

nectorresistancesandprotectioncircuitry.Improvements

in both conducted and radiated EMI also directly accrue

as a result of the reduced RMS input current and voltage.

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 2 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 op-

eration are not just limited to a narrow operating range,

for most applications is that 2-phase operation will reduce

the input capacitor requirement to that for just one chan-

nel operating at maximum current and 50% duty cycle.

IIN(MEAS) = 2.53ARMS

IIN(MEAS) = 1.55ARMS

38903 F01

5V SWITCH

20V/DIV

3.3V SWITCH

20V/DIV

INPUT CURRENT

5A/DIV

INPUT VOLTAGE

500mV/DIV

INPUT VOLTAGE (V)

3.0

2.5

2.0

1.5

1.0

0.5

38903 F02

SINGLE PHASE

DUAL CONTROLLER

2-PHASE

DUAL CONTROLLER

VO1 = 5V/3A

VO2 = 3.3V/3A

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