5
DEMO MANUAL DC236
DESIGN-READY SWITCHERS
Theory and Benefits of 2-Phase Operation
The LTC1628 dual high efficiency DC/DC controller brings
the considerable benefits of 2-phase operation to portable
applications for the first time. Notebook computers, PDAs,
handheld terminals and automotive electronics will all
benefit from the lower input filtering requirement, reduced
electromagnetic interference (EMI) and increased effi-
ciency associated with 2-phase operation.
Why the need for 2-phase operation? Before the LTC1628,
constant-frequency dual switching regulators operated
both channels in phase (i.e., 1-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 capaci-
tor and battery. These large amplitude current pulses
increased the total RMS current flowing 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 com-
ing from the switches, greatly reducing the overlap time
where they add together. The result is a significant reduc-
tion 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 3 compares the input waveforms for a representa-
tive 1-phase dual switching regulator to the new LTC1628
2-phase dual switching regulator. An actual measurement
of the RMS input current under these conditions shows
5V SWITCH: 20V/DIV
3.3V SWITCH: 20V/DIV
INPUT CURRENT: 5A/DIV
INPUT VOLTAGE: 500mV/DIV
(a)
I
IN(MEAS)
= 2.53A
RMS
DC236 F03a
Typical Single-Phase
(b)
I
IN(MEAS)
= 1.55A
RMS
DC236 F03b
LTC1628 2-Phase
Figure 3. Input Waveforms Comparing Single-Phase and 2-Phase 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
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