High Efficiency, High Density 3-Phase Supply Delivers 60A with Power Saving Stage Shedding, Active Voltage Positioning and Nonlinear Control for Superior Load Step Response Design Note 489 Jian Li and Kerry Holliday Introduction The LTC ®3829 is a feature-rich single output 3-phase synchronous buck controller that meets the power density demands of modern high speed, high capacity data processing systems, telecom systems, industrial equipment and DC power distribution systems. The LTC3829’s features include: • 4.5V to 38V input range and 0.6V to 5V output range
• 3-phase operation for low input current ripple and output voltage ripple with Stage Shedding™ mode to yield high light load efficiency • On-chip drivers in a 38-pin 5mm × 7mm QFN (or 38-pin FE) package to satisfy demanding space requirements L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks and Stage Shedding is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. VIN
VIN 10μF 16V X5R
2.2Ω VIN
100k 0.1μF DIFFOUT
30.1k
13.5k
13 14
40.2k
15
VOSENSE
–
1
VOSENSE
+
2 0Ω
66.5Ω DIFFOUT EXTVCC PGOOD ITEMP
38 4 23 17 37 39 9
RUN
IFAST
MODE
ILIM
VIN INTVCC
VFB
BOOST1
ITH ISET
TG1
DIFFN
SW1
DIFFP
BG1
DIFFOUT
BOOST2
EXTVCC PGOOD
TG2
ITEMP
SW2
GND
BG2 BOOST3
TK/SS
5 C21 1000pF
6
7 C22 1000pF
4.7μF 16V
Q1
L1 0.33μH
D1 CMDSH-3
Q3
Q4
8 11 C23 1000pF
TG3 SW3 BG3
S1P
180μF 16V
S1N
25 RSENSE1 0.001Ω
24 33 32
0.1μF
SW1
30
BG1
0.1μF
10μF 16V X5R
Q1,Q5,Q9: RJK0305DPB Q3,Q4,Q7,Q8,Q11,Q12: RJK0330DPB
TG2
28
SW2
29
BG2
VOSENSE+ Q5
D3 CMDSH-3
L2 0.33μH
S2P
S2N VOUT
19 20
330μF 2.5V SANYO w2
+
VIN
26 27
100μF 6.3V X5R
TG1
31 D2 CMDSH-3
LTC3829
AVP
SENSE1+
CSS 0.1μF
CLKOUT
VIN 7V TO 14V
+
GND
36
SENSE3+
1nF
34
SENSE2–
CLKOUT
PLLIN
47pF
SENSE1– SENSE2+
20.0k
FREQ
18 16 10 35 3
180μF 16V
INTVCC
PLLIN
SENSE3–
100pF
MODE RUN 40.2k
+
0.1μF
Q7
RSENSE2 0.001Ω
Q8
10Ω 330μF 2.5V SANYO w2
100μF 6.3V X5R
21
+
22 VIN
12
10Ω 10μF 16V X5R
R26 100Ω S3N
VOSENSE
–
R25 100Ω S3P
TG3
R24 100Ω S2N R23 100Ω
Q9
L3 0.33μH
Q11
Q12
SW3
S2P
S3P
R22 100Ω S1N R21 100Ω
BG3
S1P
S3N
RSENSE3 0.001Ω
100μF 6.3V X5R
+
330μF 2.5V SANYO w2 DN489 F01
Figure 1. A 1.5V/60A 3-Phase Converter Featuring the LTC3829 04/11/489
GND
VOUT 1.5V 60A
• Remote output voltage sensing and inductor DCR temperature compensation for accurate regulation • Active voltage positioning (AVP) and nonlinear control ensure impressive load transient performance 1.5V/60A, 3-Phase Power Supply Figure 1 shows a 7V to 14V input, 1.5V/60A output application. The LTC3829’s three channels run 120° out-of-phase, which reduces input RMS current ripple and output voltage ripple compared to single-channel solutions. Each phase uses one top MOSFET and two bottom MOSFETs to provide up to 20A of output current. The LTC3829 includes unique features that maximize efficiency, including strong gate drivers, short dead times and a programmable Stage Shedding mode, where two of the three phases shut down at light load. Onset of Stage Shedding mode can be programmed from no load to 30% load. Figure 2 shows the efficiency of this regulator at over 86.5% with a 12V input and a 1.5V/60A output with Stage Shedding mode, dramatically increasing light load efficiency. The current mode control architecture of the LTC3829 ensures that DC load current is evenly distributed among the three channels, as shown in Figure 3. Dynamic, cycleby-cycle current sharing performance is similarly tight in the face of load transients. 90
1 PHASE
3 PHASE
A fast and controlled transient response is another important requirement for modern power supplies. The LTC3829 includes two features that reduce the peakto-peak output voltage excursion during a load step: programmable nonlinear control or programmable active voltage positioning (AVP). Figure 4 shows the transient response without these features enabled. Figure 5 shows that nonlinear control improves peak-to-peak response by 17%. Figure 6 shows that AVP can achieve a 50% reduction in the amplitude of voltage spikes. Conclusion The LTC3829’s tiny 5mm × 7mm 38-pin QFN package belies its expansive feature set. It produces high efficiency with a combination of strong integrated drivers and Stage Shedding/Burst Mode® operation. It supports temperature compensated DCR sensing for high reliability. AVP and nonlinear control improve transient response with minimum output capacitance. Voltage tracking, multichip operation and external sync capability fill out its menu of features. The LTC3829 is ideal for high current applications such as telecom and datacom systems, industrial and computer systems.
IO 20A/DIV
85
EFFICIENCY (%)
200mV
VO 100mV/DIV
60A
100μs/DIV VIN = 12V VO = 1.5V fSW = 400kHz L = 330nH RSENSE = 1mΩ QT = RJK0305DPB QB = 2w RJK0330DPB
80
DN489 F04
Figure 4. Transient Performance without AVP and Nonlinear Control 166mV
VO 100mV/DIV
STAGE SHEDDING CCM 75 1
10 LOAD CURRENT (A)
100 DN489 F02
Figure 2. Efficiency Comparison of Stage Shedding vs CCM VOLTAGE ACROSS SENSE RESISTOR (mV)
22 18
60A
100μs/DIV
VIN = 12V VO = 1.5V
20
IO 20A/DIV
DN489 F05
Figure 5. Transient Performance with Nonlinear Control
16 14 12
VO 100mV/DIV
10 8
125mV
6 4 FIRST PHASE SECOND PHASE THIRD PHASE
2 0 –2
0
10
20 30 40 LOAD CURRENT (A)
50
60
DN489 F03
IO 20A/DIV
60A
100μs/DIV
DN489 F06
Figure 6. Transient Performance with AVP
Figure 3. Current Sharing Performance Between Phases Data Sheet Download
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