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LTC1629-6

16296f

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Desktop Computers

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Internet Servers

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Large Memory Arrays

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DC Power Distribution Systems

APPLICATIO S

PolyPhase, Synchronous

Step-Down Switching Regulator

The LTC

1629-6 is a PolyPhase

synchronous stepdown

current mode switching regulator controller with 0.6V

reference 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 300kHz 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

multiplies the fundamental frequency by the number

of channels 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

LTC1629-6 includes a power good output pin that

indicates when the output voltage is inside the ±10%

tolerance window.

Figure 1. High Current Dual Phase Step-Down Converter

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Reduces Required Input Capacitance and Power

Supply Induced Noise

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True Remote Sensing Differential Amplifier

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0.6V,

1% Voltage Reference Accuracy

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PolyPhase Controller Operates from Two to Twelve

Phases

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Current Mode Control Ensures Current Sharing

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Phase-Lockable Fixed Frequency: 150kHz to 300kHz

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1.8MHz Effective Switching Frequency Capability

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OPTI-LOOP

Compensation Reduces C

OUT

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Power Good Output Voltage Monitor

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Wide V

Range: 4V to 36V Operation

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Very Low Dropout Operation: 99% Duty Cycle

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Adjustable Soft-Start Current Ramping

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Internal Current Foldback Plus Shutdown Timer

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Overvoltage Soft-Latch Eliminates Nuisance Trips

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Micropower Shutdown

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Available in 28-Lead SSOP Package

1629 TA01

TG1

BOOST1

SW1

BG1

PGND

SENSE1

–

TG2

BOOST2

SW2

BG2

INTV

SENSE2

–

CLKOUT

RUN/SS

EAIN

DIFFOUT

–

LTC1629-6

SGND

0.1µF

PGOOD

0.1µF

10k

3300pF

10Ω

1.5k

60.4k

10µF ×6

35V

CERAMIC

OUT

270µF ×4

L1, L2: CEPH149-IROMC-HC

OUT

: T510E108K004AS

D1, D2: UPS840

M1, M3: Si7840DP

M2, M4: Si7440DP

OUT

0.7V/40A

1µH

0.002Ω

5V TO 15V

1µH

×2

0.47µF

10µF CER

X5R

0.002Ω

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

, 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.

Summary of content (28 pages)

PAGE 1
LTC1629-6 PolyPhase, Synchronous Step-Down Switching Regulator DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Reduces Required Input Capacitance and Power Supply Induced Noise True Remote Sensing Differential Amplifier 0.6V, ±1% Voltage Reference Accuracy PolyPhase Controller Operates from Two to Twelve Phases Current Mode Control Ensures Current Sharing Phase-Lockable Fixed Frequency: 150kHz to 300kHz 1.
PAGE 2
LTC1629-6 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage (VIN).........................36V to – 0.3V Topside Driver Voltages (BOOST1,2) .........42V to – 0.3V Switch Voltage (SW1, 2) .............................36V to – 5 V SENSE1+, SENSE2 +, SENSE1–, SENSE2 – Voltages ........................ (1.1)INTVCC to – 0.3V EAIN, VOS+, VOS–, EXTVCC, INTVCC, RUN/SS, PGOOD Voltages ...........................7V to – 0.3V Boosted Driver Voltage (BOOST-SW) ..........
PAGE 3
LTC1629-6 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VRUN/SS = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX ISCL RUN/SS Discharge Current Soft Short Condition VEAIN = 0.4V; VRUN/SS = 4.5V 0.5 2 4 ISDLDO Shutdown Latch Disable Current VEAIN = 0.4V 1.
PAGE 4
LTC1629-6 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VRUN/SS = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.995 1 1.
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LTC1629-6 U W TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Input Voltage and Mode INTVCC and EXTVCC Switch Voltage vs Temperature EXTVCC Voltage Drop 1000 250 5.05 EXTVCC VOLTAGE DROP (mV) SUPPLY CURRENT (µA) 800 EXTVCC PIN OPEN 600 400 200 INTVCC AND EXTVCC SWITCH VOLTAGE (V) ON 200 150 100 50 SHUTDOWN 0 0 20 15 10 25 INPUT VOLTAGE (V) 5 30 0 35 10 0 30 20 CURRENT (mA) 40 1629 G04 4.85 4.80 EXTVCC SWITCHOVER THRESHOLD 4.
PAGE 6
LTC1629-6 U W TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation VITH vs VRUN/SS 2.5 FCB = 0V VIN = 15V FIGURE 1 100 VOSENSE = 0.7V 2.0 –0.2 50 ISENSE (µA) –0.1 VITH (V) NORMALIZED VOUT (%) 0.0 SENSE Pins Total Source Current 1.5 1.0 –0.3 0 –50 0.5 –0.
PAGE 7
LTC1629-6 U W TYPICAL PERFOR A CE CHARACTERISTICS Current Sense Pin Input Current vs Temperature EXTVCC Switch Resistance vs Temperature 10 350 VOUT = 5V VPLLFLTR = 2.4V 33 31 29 27 25 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 300 8 6 4 200 VPLLFLTR = 0V 150 100 50 50 25 0 75 TEMPERATURE (°C) 1629 G23 100 0 – 50 – 25 125 50 25 75 0 TEMPERATURE (°C) 1629 G24 Undervoltage Lockout vs Temperature 100 125 1629 G25 Shutdown Latch Thresholds vs Temperature 4.
PAGE 8
LTC1629-6 U U U PI FU CTIO S PLLIN (Pin 6): External Synchronization Input to Phase Detector. This pin is internally terminated to SGND with 50kΩ. The phase-locked loop will force the rising top gate signal of controller 1 to be synchronized with the rising edge of the PLLIN signal. PHASMD (Pin 7): Control Input to Phase Selector which determines the phase relationships between controller 1, controller 2 and the CLKOUT signal.
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LTC1629-6 W FU CTIO AL DIAGRA U U PLLIN PHASE DET FIN 50k PLLLPF RLP CLKOUT CLK1 CLP OSCILLATOR INTVCC CLK2 DUPLICATE FOR SECOND CONTROLLER CHANNEL PHASMD ±2µA DROP OUT DET DIFFOUT VOS 40k – S Q R Q BOT CB TG TOP + CIN FCB SW FORCE BOT SWITCH LOGIC 40k INTVCC BOT BG PGND A1 VOS + DB BOOST PHASE LOGIC VIN – + 40k SHDN INTVCC 40k I1 PGOOD – L – + 0.66V + – + 30k SENSE + 0.86V 5(VFB) EAIN SLOPE COMP 0.54V COUT + + RSENSE – 30k SENSE – 45k 45k VOUT 2.
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LTC1629-6 U OPERATIO (Refer to Functional Diagram) Main Control Loop Low Current Operation The LTC1629-6 uses a constant frequency, current mode step-down architecture. During normal operation, the top MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the main current comparator, I1, resets the RS latch. The peak inductor current at which I1 resets the RS latch is controlled by the voltage on the ITH pin, which is the output of the error amplifier EA.
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LTC1629-6 U OPERATIO (Refer to Functional Diagram) INTVCC/EXTVCC Power Power Good (PGOOD) Power for the top and bottom MOSFET drivers and most of the IC circuitry is derived from INTVCC. When the EXTVCC pin is left open, an internal 5V low dropout regulator supplies INTVCC power. If the EXTVCC pin is taken above 4.7V, the 5V regulator is turned off and an internal switch is turned on connecting EXTVCC to INTVCC.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO 2.5 RSENSE Selection For Output Current PLLFLTR PIN VOLTAGE (V) RSENSE1, 2 are chosen based on the required output current. The LTC1629-6 current comparator has a maximum threshold of 75mV/RSENSE and an input common mode range of SGND to 1.1(INTVCC). The current comparator threshold sets the peak inductor current, yielding a maximum average output current IMAX equal to the peak value less half the peak-to-peak ripple current, ∆IL.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO VOUT k = VIN N where k = 1, 2, …, N – 1 So the number of phases used can be selected to minimize the output ripple current and therefore the output ripple voltage at the given input and output voltages. In applications having a highly varying input voltage, additional phases will produce the best results. Accepting larger values of ∆IL allows the use of low inductances, but can result in higher output voltage ripple.
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LTC1629-6 U U W U APPLICATIO S I FOR ATIO  2 I k( VIN )  MAX  (CRSS )( f)  N  2 I  V –V PSYNC = IN OUT  MAX  1 + δ RDS(ON) VIN  N  ( ) where δ is the temperature dependency of RDS(ON), k is a constant inversely related to the gate drive current and N is the number of stages. Both MOSFETs have I2R losses but the topside N-channel equation includes an additional term for transition losses, which peak at the highest input voltage.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO These worst-case conditions are commonly used for design because even significant deviations do not offer much relief. Note that capacitor manufacturer’s ripple current ratings are often based on only 2000 hours of life. This makes it advisable to further derate the capacitor, or to choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maximum junction temperature rating for the LTC1629-6 to be exceeded. The supply current is dominated by the gate charge supply current, in addition to the current drawn from the differential amplifier output. The gate charge is dependent on operating frequency as discussed in the Efficiency Considerations section.
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LTC1629-6 U U W U APPLICATIO S I FOR ATIO OPTIONAL EXTVCC CONNECTION 5V < VSEC < 7V + CIN + VIN LTC1629-6 LTC1629-6 VIN 1N4148 VSEC TG1 EXTVCC N-CH VIN 6.8V BAT85 N-CH 1µF BAT85 RSENSE VOUT SW1 COUT BG1 VOUT L1 + + BG1 BAT85 VN2222LL EXTVCC T1 0.22µF TG1 + RSENSE SW1 + VIN CIN COUT N-CH N-CH PGND PGND 1629 F05b 1629 F05a Figure 5a.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO current required from the input power supply. If RUN/SS has been pulled all the way to ground there is a delay before starting of approximately: tDELAY = ( ) 1.5V CSS = 1.25s / µF CSS 1.2µA The time for the output current to ramp up is then: tRAMP = 3V − 1.5V CSS = (1.25s / µF ) CSS 1.2µA By pulling the RUN/SS pin below 0.8V the LTC1629-6 is put into low current shutdown (IQ < 40µA). RUN/SS can be driven directly from logic as shown in Figure 6.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO center frequency fO. A voltage applied to the PLLFLTR pin of 1.2V corresponds to a frequency of approximately 220kHz. The nominal operating frequency range of the LTC1629-6 is 140kHz to 310kHz. The phase detector used is an edge sensitive digital type which provides zero degrees phase shift between the external and internal oscillators. This type of phase detector will not lock up on input frequencies close to the harmonics of the VCO center frequency.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: %Efficiency = 100% – (L1 + L2 + L3 + ...) where L1, L2, etc. are the individual losses as a percentage of input power.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in DC (resistive) load current.
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LTC1629-6 U U W U APPLICATIO S I FOR ATIO Although the LTC1629-6 has a maximum input voltage of 36V, most applications will be limited to 30V by the MOSFET BVDSS. 50A IPK RATING Since the output voltage is below 2.4V the output resistive divider will need to be sized to not only set the output voltage but also to absorb the sense pin input current for both channels. VIN 12V TRANSIENT VOLTAGE SUPPRESSOR GENERAL INSTRUMENT 1.5KA24A R1(MIN) = LTC1629-6 1.8 V   = 10k   = 30k  2.4V − 1.
PAGE 23
LTC1629-6 U U W U APPLICATIO S I FOR ATIO The worst-case power disipated by the synchronous MOSFET under short-circuit conditions at elevated ambient temperature and estimated 50°C junction temperature rise is: ( 5.5V − 1.8 V 5.28 A 5.5V = 360mW PSYNC = ) (1.48)(0.013Ω) 2 which is much less than normal, full-load conditions. Incidentally, since the load no longer dissipates power in the shorted condition, total system power dissipation is decreased by over 99%.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO 8) Minimize the capacitive load on the CLKOUT pin to minimize excess phase shift. Buffer if necessary with an NPN emitter follower. The diagram in Figure 9 illustrates all branch currents in a 2-phase switching regulator. It becomes very clear after studying the current waveforms why it is critical to keep the high-switching-current paths to a small physical size.
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LTC1629-6 U W U U APPLICATIO S I FOR ATIO Simplified Visual Explanation of How a 2-Phase Controller Reduces Both Input and Output RMS Ripple Current A multiphase power supply significantly reduces the amount of ripple current in both the input and output capacitors. The RMS input ripple current is divided by, and the effective ripple frequency is multiplied up by the number of phases used (assuming that the input voltage is greater than the number of phases used times the output voltage).
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LTC1629-6 U TYPICAL APPLICATIO S OPTIONAL SYNC CLOCK IN L1 2 0.33µF 3 6.04k, 1% 4 5 100pF 0.33µF 6800pF 7 8 9 27.4k, 1% 10 11 12 100pF 13 14 SENSE1 + TG1 SENSE1 – SW1 EAIN BOOST1 0.003Ω 28 27 0.47µF 26 25 M1 D7 24 VIN PLLFLTR 23 PLLIN LTC1629-6 BG1 22 5V PHASMD EXTVCC 21 ITH INTVCC 20 SGND PGND 19 VDIFFOUT BG2 18 – VOS BOOST2 17 + SW2 VOS 16 TG2 SENSE2 – 15 + PGOOD SENSE2 M2 M3 D1 B320A 10Ω 1µF 1µF,25V 2X150µF 22µF 6.3V 16V GND D2 B320A 0.47µF M4 M5 M6 L2 PGOOD 0.
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LTC1629-6 U PACKAGE DESCRIPTIO G Package 28-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 10.07 – 10.33* (.397 – .407) 28 27 26 25 24 23 22 21 20 19 18 17 16 15 7.65 – 7.90 (.301 – .311) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 5.20 – 5.38** (.205 – .212) 1.73 – 1.99 (.068 – .078) 0° – 8° .13 – .22 (.005 – .009) .55 – .95 (.022 – .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) .65 (.0256) BSC .25 – .38 (.010 – .015) .05 – .21 (.002 – .
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LTC1629-6 U TYPICAL APPLICATIO L1 0.1µF 1 2 17.8k 3 10k 4 5 6.04k 1% 100pF 1000pF 6 1000pF 3.3k 8 9 10 11 27.4k 1% 12 13 14 100pF SENSE1 + TG1 – SW1 SENSE1 EAIN BOOST1 PLLFLTR VIN BG1 PLLIN PHASMD EXTVCC ITH INTVCC SGND LTC1629-6 VDIFFOUT PGND BG2 VOS – BOOST2 + SW2 VOS SENSE2 – TG2 SENSE2 + PGOOD 27 0.47µF 26 M1 M2 D1 UPS840 25 D3 24 10Ω 23 22 21 0.1µF 5V CIN 1µF,25V 20 4.7µF 6.3V COUT 19 18 D4 17 16 100k 0.