LTC3736-2 Datasheet, PDF (13/28 Pages) Linear Technology – Dual 2-Phase, No RSENSE Synchronous Controller with Output Tracking

U
OPERATIO (Refer to Functional Diagram)
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 reduc-
tion by itself, remember that power losses are propor-
tional 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-
SW1 (V)
Single Phase
Dual Controller
2-Phase
Dual Controller
SW2 (V)
I_L1
I_L2
I_IN
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Figure 2. Example Waveforms for a Single Phase
Dual Controller vs the 2-Phase LTC3736-2
LTC3736-2
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.
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)
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Figure 3. RMS Input Current Comparison
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