LTC3737 Datasheet, PDF (11/24 Pages) Linear Technology – Dual 2-Phase, No RSENSE DC/DC Controller with Output Tracking

U
OPERATIO (Refer to Functional Diagram)
Single Phase
Dual Controller
2-Phase
Dual Controller
SW1 (V)
SW2 (V)
I_L1
LTC3737
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 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 4 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.
I_L2
I_IN
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Figure 3. Example Waveforms for a Single Phase
Dual Controller vs the 2-Phase LTC3737
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 pro-
portional to I_RMS2, 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 pro-
tection circuitry. Improvements in both conducted and
radiated EMI also directly accrue as a result of the reduced
2.0
1.8
1.6
SINGLE PHASE
DUAL CONTROLER
1.4
1.2
2-PHASE
DUAL CONTROLER
1.0
0.8
0.6
0.4
0.2 ^VOUT1 ^{= 2.5V/2A}
V_OUT2 = 1.8V/2A
0
23 4 56
78
9 10
INPUT VOLTAGE (V)
3737 F04
Figure 4. RMS Input Current Comparison
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.
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