LTC3728LEGN-1#PBF Linear Technology, LTC3728LEGN-1#PBF Datasheet - Page 12

• Manufacturer Part Number: LTC3728LEGN-1#PBF
• Description: IC REG SYNC DUAL 28-SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3728LEGN-1#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 7 V
• Current - Output: 3A
• Frequency - Switching: 250kHz ~ 550kHz
• Voltage - Input: 4.5 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

OPERATION
LTC3728L-1
Figure 3 compares the input waveforms for a representa-
tive single-phase dual switching regulator to the LTC1628
2-phase dual switching regulator. An actual measurement of
the RMS input current under these conditions shows that 2-
phase operation dropped the input current from 2.53A
to 1.55A
remember that the power losses are proportional to I
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.
12
RMS
Figure 3. 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 LTC1628 2-Phase Regulator Allows
Less Expensive Input Capacitors, Reduces Shielding Requirements for EMI and Improves Effi ciency
. While this is an impressive reduction in itself,
(Refer to Functional Diagram)
I
IN(MEAS)
(a)
= 2.53A
RMS
Figure 4. RMS Input Current Comparison
3.0
2.5
2.0
1.5
1.0
0.5
0
0
V
V
O1
O2
3728L1 F03a
= 5V/3A
= 3.3V/3A
10
RMS
INPUT VOLTAGE (V)
RMS
INPUT CURRENT
INPUT VOLTAGE
DUAL CONTROLLER
3.3V SWITCH
5V SWITCH
500mV/DIV
2
20V/DIV
20V/DIV
5A/DIV
,
SINGLE PHASE
DUAL CONTROLLER
2-PHASE
20
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.
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 channel
operating at maximum current and 50% duty cycle.
30
3728L1 F04
IN
(Duty Cycle = V
40
I
IN(MEAS)
(b)
= 1.55A
RMS
OUT
/V
3728L1 F03b
IN
). Figure 4 shows how
3728l1fc