LTC3890

14

3890f

With 2-phase operation, the two channels of the dual

switching regulator are operated 180 degrees out of phase.

This effectively interleaves the current pulses drawn by the

switches, greatly reducing the overlap time where they add

together. The result is a significant reduction in total RMS

input current, which in turn allows less expensive input

capacitors to be used, reduces shielding requirements for

EMI and improves real world operating efficiency.

Figure 1 compares the input waveforms for a representa-

tive single-phase dual switching regulator to the LTC3890

2-phase dual switching regulator. An actual measurement of

the RMS input current under these conditions shows that

meaning that the actual power wasted is reduced by a fac-

tor 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/connector resistances

and protection circuitry. 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

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 channel

operating at maximum current and 50% duty cycle.

3890 F01

5V SWITCH

20V/DIV

3.3V SWITCH

20V/DIV

INPUT CURRENT

5A/DIV

INPUT VOLTAGE

500mV/DIV

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

INPUT VOLTAGE (V)

0

3.0

2.5

2.0

1.5

1.0

0.5

0

10

20

30

40

3890 F02

SINGLE PHASE

DUAL CONTROLLER

2-PHASE

DUAL CONTROLLER