Datasheet

LTC3708
12
3708fb
OPERATION
(Refer to Functional Diagram)
While this is an impressive reduction in itself, remember
that the power losses are proportional to I
2
RMS
, meaning
that the actual power wasted is reduced by a factor of
2.66. The reduced input ripple current also means that
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
voltage, V
IN
. 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 opera-
tion are not just limited to a narrow operating range, but in
INPUT VOLTAGE (V)
0
INPUT RMS CURRENT (A)
3.0
2.5
2.0
1.5
1.0
0.5
0
10 20 30 40
3708 F02
SINGLE PHASE
DUAL CONTROLLER
2-PHASE
DUAL CONTROLLER
V
O1
= 5V/3A
V
O2
= 3.3V/3A
Figure 2. RMS Input Current Comparison
fact extend over a wide region. A good rule of thumb for
most applications is that 2-phase operation will reduce the
input capacitance requirement to that for just one channel
operating at maximum current and 50% duty cycle.