ltc3827ig-1 Linear Technology Corporation, ltc3827ig-1 Datasheet - Page 12

• Manufacturer Part Number: ltc3827ig-1
• Description: Low Iq, Dual, 2-phase Synchronous Step-down Controller
• Manufacturer: Linear Technology Corporation

OPERATIO
LTC3827-1
Figure 1 compares the input waveforms for a represen-
tative single-phase dual switching regulator to the
LTC3827-1 2-phase dual switching regulator. An ac-
tual measure-ment of the RMS input current under
these conditions shows that 2-phase operation dropped
the input current from 2.53A
this is an impressive reduction in itself, remember that
the power losses are proportional to I
that the actual power wasted is reduced by a factor 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 con-
ducted and radiated EMI also directly accrue as a result
of the reduced RMS input current and voltage.
Of course, the improvement afforded by 2-phase opera-
tion is a function of the dual switching regulator’s relative
12
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
U
(Refer to Functional Diagram)
I
IN(MEAS)
RMS
= 2.53A
(a)
to 1.55A
RMS
RMS
Figure 2. RMS Input Current Comparison
3.0
2.5
2.0
1.5
1.0
0.5
0
0
RMS
2
, meaning
V
V
38271 F01a
O1
O2
= 5V/3A
= 3.3V/3A
. While
10
INPUT CURRENT
INPUT VOLTAGE
INPUT VOLTAGE (V)
3.3V SWITCH
5V SWITCH
500mV/DIV
DUAL CONTROLLER
20V/DIV
20V/DIV
5A/DIV
SINGLE PHASE
DUAL CONTROLLER
2-PHASE
20
duty cycles which, in turn, are dependent upon the input
voltage V
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
operation 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 channel
operating at maximum current and 50% duty cycle.
The schematic on the first page is a basic LTC3827-1
application circuit. External component selection is driven
by the load requirement, and begins with the selection of
R
are selected. Finally, C
SENSE
30
and the inductor value. Next, the power MOSFETs
IN
38271 F02
(Duty Cycle = V
40
I
IN(MEAS)
= 1.55A
(b)
IN
RMS
and C
OUT
/V
OUT
IN
38271 F01b
). Figure 2 shows how
are selected.
38271fd