Datasheet

LTC3736-2
13
37362fb
OPERATION
Figure 2 shows example waveforms for a single-phase
dual controller versus a 2-phase LTC3736-2 system. In this
case, 2.5V and 1.8V outputs, each drawing a load current
of 2A, are derived from a 7V (e.g., a 2-cell Li-Ion battery)
input supply. In this example, 2-phase operation would
reduce the RMS input capacitor current from 1.79A
RMS
to 0.91A
RMS
. While this is an impressive reduction by
itself, remember that power losses are proportional to
I
RMS
2
, meaning that actual power wasted is reduced by
a factor of 3.86.
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. Signifi cant cost
and board footprint savings are also realized by being able
to use smaller, less expensive, lower RMS current-rated
input capacitors.
Of course, the improvement afforded by 2-phase operation
is a function of the relative duty cycles of the two control-
lers, which in turn are dependent upon the input supply
voltage. Figure 3 depicts how the RMS input current varies
for single-phase and 2-phase dual controllers with 2.5V
and 1.8V outputs over a wide input voltage range.
It can be readily seen that the advantages of 2-phase op-
eration are not limited to a narrow operating range, but in
fact extend over a wide region. A good rule of thumb 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.
Figure 2. Example Waveforms for a Single-Phase
Dual Controller vs the 2-Phase LTC3736-2
Figure 3. RMS Input Current Comparison
Single-Phase
Dual Controller
2-Phase
Dual Controller
SW1 (V)
SW2 (V)
I
L1
I
L2
I
IN
37362 F02
INPUT VOLTAGE (V)
2
0
INPUT CAPACITOR RMS CURRENT
0.2
0.6
0.8
1.0
2.0
1.4
4
6
7
37362 F03
0.4
1.6
1.8
1.2
35
8
9
10
SINGLE-PHASE
DUAL CONTROLER
2-PHASE
DUAL CONTROLER
V
OUT1
= 2.5V/2A
V
OUT2
= 1.8V/2A
(Refer to Functional Diagram)