LTC3890EGN-1 LINER [Linear Technology], LTC3890EGN-1 Datasheet - Page 14

• Manufacturer Part Number: LTC3890EGN-1
• Description: 60V Low IQ, Dual, 2-Phase Synchronous Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

OPERATION
LTC3890-1
together. The result is a signifi cant 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 effi ciency.
Figure 1 compares the input waveforms for a representative
single-phase dual switching regulator to the LTC3890-1
2-phase dual switching regulator. An actual measure-
ment of the RMS input current under these conditions
shows that 2-phase operation dropped the input current
from 2.53A
reduction in itself, remember that the power losses are
proportional to I
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 conducted and radiated EMI also
directly accrue as a result of the reduced RMS input cur-
rent and voltage.
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
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.
14
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 Effi ciency
IN
RMS
(Duty Cycle = V
to 1.55A
RMS
(Refer to the Functional Diagram)
2
, meaning that the actual power
RMS
OUT
. While this is an impressive
I
IN(MEAS)
/V
IN
). Figure 2 shows how
= 2.53A
RMS
INPUT CURRENT
INPUT VOLTAGE
3.3V SWITCH
5V SWITCH
500mV/DIV
20V/DIV
20V/DIV
5A/DIV
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 fi rst page is a basic LTC3890-1 ap-
plication circuit. External component selection is driven
by the load requirement, and begins with the selection of
R
are selected. Finally, C
SENSE
and the inductor value. Next, the power MOSFETs
3.0
2.5
2.0
1.5
1.0
0.5
Figure 2. RMS Input Current Comparison
0
0
V
V
I
IN(MEAS)
O1
O2
= 5V/3A
= 3.3V/3A
10
= 1.55A
INPUT VOLTAGE (V)
IN
DUAL CONTROLLER
and C
RMS
SINGLE PHASE
DUAL CONTROLLER
2-PHASE
20
OUT
38901 F01
are selected
30
38901 F02
40
38901f