LTC1628CG-SYNC Linear Technology, LTC1628CG-SYNC Datasheet - Page 12

• Manufacturer Part Number: LTC1628CG-SYNC
• Description: IC SW REG STEP-DOWN SYNC 28-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1628CG-SYNC

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: Adj to 0.8V
• Current - Output: 3A
• Frequency - Switching: 140kHz ~ 310kHz
• Voltage - Input: 3.5 ~ 30 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

OPERATIO
LTC1628-SYNC
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
operation 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.
A final question: If 2-phase operation offers such an
advantage over single-phase operation for dual switching
regulators, why hasn’t it been done before? The answer is
that, while simple in concept, it is hard to implement.
Constant-frequency current mode switching regulators
require an oscillator derived “slope compensation” signal
to allow stable operation of each regulator at over 50%
duty cycle. This signal is relatively easy to derive in single-
phase dual switching regulators, but required the develop-
ment of a new and proprietary technique to allow 2-phase
12
IN
(Duty Cycle = V
U
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-SYNC 2-Phase Regulator Allows Less Expensive Input Capacitors,
Reduces Shielding Requirements for EMI and Improves Efficiency
(Refer to Functional Diagram)
OUT
I
IN(MEAS)
/V
IN
= 2.53A
(a)
). Figure 4 shows how
RMS
DC236 F03a
INPUT CURRENT
INPUT VOLTAGE
3.3V SWITCH
5V SWITCH
500mV/DIV
20V/DIV
20V/DIV
5A/DIV
operation. In addition, isolation between the two channels
becomes more critical with 2-phase operation because
switch transitions in one channel could potentially disrupt
the operation of the other channel.
The LTC1628-SYNC is proof that these hurdles have been
surmounted. The new device offers unique advantages for
the ever-expanding number of high efficiency power sup-
plies required in portable electronics.
3.0
2.5
2.0
1.5
1.0
0.5
Figure 4. RMS Input Current Comparison
0
0
V
V
I
IN(MEAS)
O1
O2
= 5V/3A
= 3.3V/3A
10
= 1.55A
(b)
INPUT VOLTAGE (V)
DUAL CONTROLLER
RMS
SINGLE PHASE
DUAL CONTROLLER
2-PHASE
20
DC236 F03b
30
1628 F04
40
1628syncfa