LTC3890
operaTion (Refer to the Functional Diagram)
With 2-phase operation, the two channels of the dual
switchingregulatorareoperated180degreesout-of-phase.
Thiseffectivelyinterleavesthecurrentpulsesdrawnbythe
switches,greatlyreducingtheoverlaptimewheretheyadd
together. The result is a significant reduction in total RMS
input current, which in turn allows less expensive input
capacitors to be used, reduces shielding requirements for
EMI and improves real world operating efficiency.
voltage V (Duty Cycle = V /V ). Figure 2 shows how
IN
OUT IN
theRMSinputcurrentvariesforsingle-phaseand2-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 op-
eration are not just limited to a narrow operating range,
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.
Figure 1 compares the input waveforms for a representa-
tive single-phase dual switching regulator to the LTC3890
2-phasedualswitchingregulator.Anactualmeasurementof
the RMS input current under these conditions shows that
3.0
SINGLE PHASE
2-phaseoperationdroppedtheinputcurrentfrom2.53A
RMS
DUAL CONTROLLER
2.5
2.0
1.5
1.0
0.5
0
to1.55A
.Whilethisisanimpressivereductioninitself,
RMS
2
rememberthatthepowerlossesareproportionaltoI
,
RMS
meaning that the actual power wasted is reduced by a fac-
tor of 2.66. The reduced input ripple voltage also means
less power is lost in the input power path, which could
include batteries, 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.
2-PHASE
DUAL CONTROLLER
V
O1
V
O2
= 5V/3A
= 3.3V/3A
0
10
20
30
40
INPUT VOLTAGE (V)
3890 F02
Of course, the improvement afforded by 2-phase opera-
tion is a function of the dual switching regulator’s relative
duty cycles which, in turn, are dependent upon the input
Figure 2. RMS Input Current Comparison
5V SWITCH
20V/DIV
3.3V SWITCH
20V/DIV
INPUT CURRENT
5A/DIV
INPUT VOLTAGE
500mV/DIV
3890 F01
I
= 2.53A
I = 1.55A
IN(MEAS) RMS
IN(MEAS)
RMS
Figure 1. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for Dual Switching Regulators
Converting 12V to 5V and 3.3V at 3A Each. The Reduced Input Ripple with the 2-Phase Regulator Allows
Less Expensive Input Capacitors, Reduces Shielding Requirements for EMI and Improves Efficiency
3890fb
14
Linear Systems [ Linear Systems ]
