LTC3836_15 Datasheet, PDF (13/30 Pages) Linear Technology – Dual 2-Phase, No RSENSETM Low VIN Synchronous Controller

LTC3836
OPERATION (Refer to Functional Diagram)
Figure 2 shows example waveforms for a single phase dual
controller versus a 2-phase LTC3836 system. In this case,
two outputs of different voltage, each drawing the same
load current are derived from a single input supply. In this
example, 2-phase operation could halve the RMS input
capacitor current. While this is an impressive reduction
by itself, remember that power losses are proportional
to I_RMS2, meaning that just one-fourth the actual power
is wasted.
Single Phase
Dual Controller
2-Phase
Dual Controller
SW1 (V)
SW2 (V)
The reduced input ripple current also means that less power
is lost in the input power path, which could include batter-
ies, 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. 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 3 depicts how the RMS input current varies
for single phase and 2-phase dual controllers with 2.5V and
1.8V outputs. 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.
I_L1
I_L2
I_IN
3836 F02
Figure 2. Example Waveforms for a Single Phase
Dual Controller vs the 2-Phase LTC3836
2.0
1.8
SINGLE PHASE
DUAL CONTROLLER
1.6
1.4
1.2
1.0
0.8
2-PHASE
0.6
DUAL CONTROLLER
0.4
0.2 ^VOUT1 ^{= 2.5V/2A}
V_OUT2 = 1.8V/2A
0
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
3836 F03
Figure 3. RMS Input Current Comparison
3836fb
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