LTC3736-2 Linear Technology, LTC3736-2 Datasheet - Page 13

• Manufacturer Part Number: LTC3736-2
• Description: Synchronous Controller
• Manufacturer: Linear Technology

OPERATIO
SW1 (V)
SW2 (V)
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
tion by itself, remember that power losses are propor-
tional to I
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 pro-
I
I
I
L1
L2
IN
RMS
Figure 2. Example Waveforms for a Single Phase
Dual Controller vs the 2-Phase LTC3736-2
Dual Controller
to 0.91A
Single Phase
RMS
2
, meaning that actual power wasted is
U
RMS
(Refer to Functional Diagram)
. While this is an impressive reduc-
Dual Controller
2-Phase
37362 F02
tection circuitry. Improvements in both conducted and
radiated EMI also directly accrue as a result of the reduced
RMS input current and voltage. Significant 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 opera-
tion is a function of the relative duty cycles of the two
controllers, 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 control-
lers with 2.5V and 1.8V outputs over a wide input voltage
range.
It can be readily seen that the advantages of 2-phase
operation 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 3. RMS Input Current Comparison
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
2
V
V
OUT1
OUT2
3
= 2.5V/2A
= 1.8V/2A
4
INPUT VOLTAGE (V)
DUAL CONTROLER
SINGLE PHASE
5
6
DUAL CONTROLER
7
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2-PHASE
8
LTC3736-2
9
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10
13
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