LTC3826_15 Datasheet, PDF(14/36 Page) Linear Technology – 30A IQ, Dual, 2-Phase Synchronous Step-Down Controller

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LTC3826_15 Datasheet, PDF (14/36 Pages) Linear Technology – 30A IQ, Dual, 2-Phase Synchronous Step-Down Controller

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LTC3826

OPERATION (Refer to Functional Diagram)

THEORY AND BENEFITS OF 2-PHASE OPERATION

Why the need for 2-phase operation? Up until the 2-phase

family, constant-frequency dual switching regulators

operated both channels in phase (i.e., single-phase

operation). This means that both switches turned on at

the same time, causing current pulses of up to twice the

amplitude of those for one regulator to be drawn from the

input capacitor and battery. These large amplitude current

pulses increased the total RMS current ï¬owing from the

input capacitor, requiring the use of more expensive input

capacitors and increasing both EMI and losses in the input

capacitor and battery.

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 signiï¬cant 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 efï¬ciency.

Figure 1 compares the input waveforms for a representa-

tive single-phase dual switching regulator to the LTC3826

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

proportional to IRMS2, meaning that the actual power wasted

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

voltage also means less power is lost in the input power

5V SWITCH

20V/DIV

3.3V SWITCH

20V/DIV

INPUT CURRENT

5A/DIV

INPUT VOLTAGE

500mV/DIV

IIN(MEAS) = 2.53ARMS

(a)

3826 F01a

IIN(MEAS) = 1.55ARMS

(b)

3826 F01b

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 Efï¬ciency

3826fc

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