LTC3890EGN-1#PBF Linear Technology, LTC3890EGN-1#PBF Datasheet - Page 14

• Manufacturer Part Number: LTC3890EGN-1#PBF
• Description: IC BUCK SYNC ADJ 25A DUAL 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3890EGN-1#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 24 V
• Current - Output: 25A
• Frequency - Switching: 50kHz ~ 900kHz
• Voltage - Input: 4 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Primary Input Voltage: 12V
• No. Of Outputs: 2
• Output Voltage: 24V
• Output Current: 25A
• No. Of Pins: 32
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Min: 4V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

OPERATION
With 2-phase operation, the two channels of the dual
switching regulator are operated 180 degrees out-of-phase.
This effectively interleaves the current pulses drawn by the
switches, greatly reducing the overlap time where they add
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.
Figure 1 compares the input waveforms for a representa-
tive single-phase dual switching regulator to the LTC3890
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.
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
LTC3890
14
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
. While this is an impressive reduction in itself,
(Refer to the Functional Diagram)
I
IN(MEAS)
= 2.53A
RMS
RMS
RMS
INPUT CURRENT
INPUT VOLTAGE
3.3V SWITCH
2
5V SWITCH
500mV/DIV
,
20V/DIV
20V/DIV
5A/DIV
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 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.
IN
Figure 2. RMS Input Current Comparison
3.0
2.5
2.0
1.5
1.0
0.5
(Duty Cycle = V
0
0
I
IN(MEAS)
V
V
O1
O2
= 5V/3A
= 3.3V/3A
= 1.55A
10
INPUT VOLTAGE (V)
DUAL CONTROLLER
RMS
OUT
2-PHASE
SINGLE PHASE
DUAL CONTROLLER
20
/V
IN
). Figure 2 shows how
3890 F01
30
3890 F02
40
3890fa