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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