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FEATURES
Wide V
Range: 4V to 36V Operation
IN
Reduces Required Input Capacitance and Power
Supply Induced Noise
±
1% Output Voltage Accuracy
Phase-Lockable Fixed Frequency: 250kHz to 550kHz
True Remote Sensing Differential Amplifier
TM
PolyPhase
Extends from Two to Twelve Phases
Reduces the Size and Value of Inductors
Current Mode Control Ensures Current Sharing
1.1MHz Effective Switching Frequency (2-Phase)
®
OPTI-LOOP
Compensation Reduces C
Power Good Output Voltage Indicator
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Internal Current Foldback Plus Shutdown Timer
Overvoltage Soft-Latch Eliminates Nuisance Trips
Available in 5mm × 5mm QFN
and 28-Lead SSOP Packages
U
APPLICATIO S
Desktop Computers/Servers
Large Memory Arrays
DC Power Distribution Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a registered trademark of Linear Technology Corporation.
PolyPhase is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
S
0.1µF
3.3k
1000pF
S
16k
S
16k
C
OUT
D1, D2: UP5840
Step-Down Switching Regulator
OUT
10Ω
LTC3729
V
TG1
IN
S
BOOST1
0.47µF
SW1
S
RUN/SS
BG1
PGND
PGOOD
+
SENSE1
I
TH
–
SENSE1
TG2
S
SGND
BOOST2
0.47µF
SW2
S
S
V
BG2
DIFFOUT
EAIN
INTV
S
CC
10µF
–
+
V
SENSE2
OS
+
–
V
SENSE2
OS
: T510E108K004AS
L1, L2: CEPH149-IROMC
Figure 1. High Current Dual Phase Step-Down Converter
550kHz, PolyPhase,
High Efficiency, Synchronous
DESCRIPTIO
®
The LTC
3729 is a multiple phase, synchronous step-
down current mode switching regulator controller that
drives N-channel external power MOSFET stages in a
phase-lockable fixed frequency architecture. The PolyPhase
controller drives its two output stages out of phase at
frequencies up to 550kHz to minimize the RMS ripple
currents in both input and output capacitors. The output
clock signal allows expansion for up to 12 evenly phased
controllers for systems requiring 15A to 200A of output
current. The multiple phase technique effectively multi-
plies the fundamental frequency by the number of chan-
nels used, improving transient response while operating
each channel at an optimum frequency for efficiency.
Thermal design is also simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply's positive and negative
output terminals as required for high current applications.
A RUN/SS pin provides both soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
dissipation during short-circuit conditions when the
overcurrent latchoff is disabled. OPTI-LOOP compensa-
tion allows the transient response to be optimized over a
wide range of output capacitance and ESR values. The
LTC3729 includes a power good output pin that indicates
when the output is within ±7.5% of the designed set point.
M1
0.002Ω
L1
M2
D1
0.8µH
×2
M3
0.002Ω
L2
M4
0.8µH
×2
D2
M1, M3: IRF7811W
M2, M4: IRF7822
LTC3729
V
IN
5V TO 28V
10µF
35V
CERAMIC
×4
V
OUT
1.6V/40A
+
C
OUT
1000µF ×2
4V
3729 TA01
sn3729 3729fas
1
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Related Manuals for Linear Technology LTC3729
Summary of Contents for Linear Technology LTC3729
- Page 1 ESR values. The LTC3729 includes a power good output pin that indicates , LTC and LT are registered trademarks of Linear Technology Corporation. OPTI-LOOP is a registered trademark of Linear Technology Corporation. when the output is within ±7.5% of the designed set point.
- Page 2 LTC3729 ABSOLUTE AXI U RATI GS (Note 1) Input Supply Voltage (V )......36V to – 0.3V Voltage ..........2.7V to – 0.3V Topside Driver Voltages (BOOST1,2) ..42V to – 0.3V Peak Output Current <1µs(TGL1,2, BG1,2) ....5A Switch Voltage (SW1, 2) ......36V to – 5 V INTV RMS Output Current ........
- Page 3 LTC3729 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C. V = 15V, V = 5V unless otherwise noted. RUN/SS SYMBOL PARAMETER CONDITIONS UNITS Reference Voltage Line Regulation = 3.6V to 30V (Note 3) 0.002...
- Page 4 Note 6: The LTC3729E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating Note 3: The LTC3729 is tested in a feedback loop that servos V to a temperature range are assured by design, characterization and correlation...
- Page 5 LTC3729 TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Input Voltage INTV and EXTV Switch and Mode EXTV Voltage Drop Voltage vs Temperature 1000 5.05 INTV VOLTAGE 5.00 4.95 4.90 4.85 4.80 EXTV SWITCHOVER THRESHOLD 4.75 SHUTDOWN 4.70 – 50 –...
- Page 6 LTC3729 TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation vs V SENSE Pins Total Source Current RUN/SS FCB = 0V = 0.7V OSENSE = 15V FIGURE 1 –0.1 –0.2 –0.3 –50 –0.4 –100 LOAD CURRENT (A) COMMON MODE VOLTAGE (V) RUN/SS...
- Page 7 LTC3729 TYPICAL PERFOR A CE CHARACTERISTICS Current Sense Pin Input Current EXTV Switch Resistance Oscillator Frequency vs Temperature vs Temperature vs Temperature = 5V = 2.4V PLLFLTR = 1.2V PLLFLTR = 0V PLLFLTR –50 –25 –50 –25 – 50 – 25 TEMPERATURE (°C)
- Page 8 LTC3729 PI FU CTIO S G Package/UH Package PLLFLTR (Pin 5/Pin 2): The Phase-Locked Loop’s Low SW2, SW1 (Pins 17, 26/Pins 15, 25): Switch Node Pass Filter is tied to this pin. Alternatively, this pin can be Connections to Inductors. Voltage swing at these pins is...
- Page 9 LTC3729 FU CTIO AL DIAGRA PLLIN INTV PHASE DET DUPLICATE FOR SECOND BOOST CONTROLLER CHANNEL PLLLPF DROP CLKOUT CLK1 OSCILLATOR CLK2 FORCE BOT SWITCH PHASMD INTV LOGIC PHASE LOGIC ±2µA DIFFOUT PGND – SHDN INTV – – SENSE – 0.86V SENSE –...
- Page 10 Input capacitance ESR requirements and efficiency losses leased allowing normal operation to resume. When the RUN/SS pin is low, all LTC3729 functions are shut down. are substantially reduced because the peak current drawn from the input capacitor is effectively divided by the...
- Page 11 ±7.5% of its nominal output level as determined by APPLICATIO S I FOR ATIO Selection For Output Current The basic LTC3729 application circuit is shown in Figure 1 SENSE on the first page. External component selection is driven are chosen based on the required output...
- Page 12 Operating Frequency stages to run at a lower fundamental frequency, enhancing efficiency. The LTC3729 uses a constant frequency, phase-lockable architecture with the frequency determined by an internal The inductor value has a direct effect on ripple current. The inductor ripple current ∆I capacitor.
- Page 13 When the powdered iron cores, forcing the use of more expensive ® LTC3729 is operating in continuous mode the duty factors ferrite, molypermalloy, or Kool Mµ cores. Actual core for the top and bottom MOSFETs of each output stage are...
- Page 14 LTC3729 APPLICATIO S I FOR ATIO and C Selection 1 δ MAIN DS ON In continuous mode, the source current of each top N-channel MOSFET is a square wave of duty cycle V ...
- Page 15 ) and SENSE regulator powers the drivers and internal circuitry of the > 1/(8Nf)(R LTC3729. The INTV pin regulator can supply up to 50mA SENSE peak and must be bypassed to power ground with a The emergence of very low ESR capacitors in small, minimum of 4.7µF tantalum or electrolytic capacitor.
- Page 16 LTC3729 APPLICATIO S I FOR ATIO maximum junction temperature rating for the LTC3729 to EXTV and the V pin, to prevent current from backfeeding be exceeded. The supply current is dominated by the gate charge supply current, in addition to the current drawn Significant efficiency gains can be realized by powering from the differential amplifier output.
- Page 17 A small pull-up current (>5µA) supplied to the RUN/ The LTC3729 has a true remote voltage sense capablity. SS pin will prevent the overcurrent latch from operating. The sensing connections should be returned from the load The following explanation describes how the functions back to the differential amplifier’s inputs through a com-...
- Page 18 µ 1 25 RAMP µ By pulling the RUN/SS pin below 0.8V the LTC3729 is put into low current shutdown (I < 40µA). RUN/SS can be driven directly from logic as shown in Figure 6. Diode D1 *OPTIONAL TO DEFEAT OVERCURRENT LATCHOFF...
- Page 19 Minimum On-Time Considerations Minimum on-time t is the smallest time duration 2.4V ON(MIN) that the LTC3729 is capable of turning on the top MOSFET. PHASE DETECTOR It is determined by internal timing delays and the gate EXTERNAL charge required to turn on the top MOSFET. Low duty cycle...
- Page 20 GATECHG are the gate charges of the topside and bottom side 3729 F08 MOSFETs. Figure 8. Active Voltage Positioning Applied to the LTC3729 Supplying INTV power through the EXTV switch input The resistive load reduces the DC loop gain while main-...
- Page 21 200µF to 300µF of capacitance having a resulting from the step change in output current may not maximum of 10mΩ to 20mΩ of ESR. The LTC3729 be within the bandwidth of the feedback loop, so this signal PolyPhase architecture typically halves to quarters this cannot be used to determine phase margin.
- Page 22 LTC3729 APPLICATIO S I FOR ATIO Design Example (Using Two Phases) The power dissipation on the topside MOSFET can be easily estimated. Using a Siliconix Si4420DY for example; As a design example, assume V = 5V (nominal), V = 5.5V = 0.013Ω, C...
- Page 23 1) Are the signal and power grounds segregated? The Incidentally, since the load no longer dissipates power in LTC3729 signal ground pin should return to the (–) plate the shorted condition, total system power dissipation is of C separately.
- Page 24 LTC3729 APPLICATIO S I FOR ATIO The diagram in Figure 9 illustrates all branch currents in a bottom plate(s) of the input capacitor(s) with a short 2-phase switching regulator. It becomes very clear after isolated PC trace since very high switched currents are studying the current waveforms why it is critical to keep present.
- Page 25 LTC3729 APPLICATIO S I FOR ATIO currents are reduced by using an additional phase. The Simplified Visual Explanation of How a 2-Phase input current peaks drop in half and the frequency is Controller Reduces Both Input and Output RMS Ripple doubled for a 2-phase converter.
- Page 26 LTC3729 TYPICAL APPLICATIO S OPTIONAL SYNC 0.003Ω CLOCK IN 1000pF RUN/SS CLKOUT 0.33µF SENSE1 0.47µF – SENSE1 8.06k, 1% MBRS EAIN BOOST1 10Ω 340T3 PLLFLTR LTC3729 1µF 0.33µF PLLIN 3X330µF, 6.3V PHASMD EXTV 1µF,6.3V 6800pF 22µF 2X150µF POSCAP INTV 6.3V...
- Page 27 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
- Page 28 550kHz, 2-Phase Dual Output Synchronous Step-Down Controller SSOP and QFN Packages Burst Mode is a registered trademark of Linear Technology Corporation. Adaptive Power is a trademark of Linear Technology Corporation. sn3729 3729fas LT/CPI 0302 1.5K REV A • PRINTED IN USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417...
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