LTC3728LCGN-PBF Datasheet, PDF (15/38 Pages) Linear Technology – Dual, 550kHz, 2-Phase Synchronous Regulators

LTC3728L/LTC3728LX
operation (Refer to Functional Diagram)
duty cycles which, in turn, are dependent upon the input
voltage V_IN (Duty Cycle = V_OUT/V_IN). Figure 4 shows how
the RMS input current varies for single-phase and 2-phase
operation for 3.3V and 5V regulators over a wide input
voltage range.
It can readily be seen that the advantages of 2-phase opera-
tion are not just 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 chan-
nel operating at maximum current and 50% duty cycle.
A final question: If 2-phase operation offers such an ad-
vantage over single-phase operation for dual switching
regulators, why hasn’t it been done before? The answer
is that, while simple in concept, it is hard to implement.
Constant-frequency, current mode switching regulators
require an oscillator derived slope compensation signal
to allow stable operation of each regulator at over 50%
duty cycle. This signal is relatively easy to derive in
single-phase dual switching regulators, but required the
development of a new and proprietary technique to allow
2-phase operation. In addition, isolation between the two
channels becomes more critical with 2-phase operation
because switch transitions in one channel could potentially
disrupt the operation of the other channel.
These 2-phase parts are proof that these hurdles have
been surmounted. They offer unique advantages for the
ever expanding number of high efficiency power supplies
required in portable electronics.
3.0
SINGLE PHASE
2.5
DUAL CONTROLLER
2.0
1.5
2-PHASE
DUAL CONTROLLER
1.0
0.5 _{VO1 = 5V/3A}
V_O2 = 3.3V/3A
0
0
10
20
30
INPUT VOLTAGE (V)
40
3728 F04
Figure 4. RMS Input Current Comparison
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