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LTC1629/LTC1629-PG

PolyPhase, High Efficiency,

Synchronous Step-Down Switching Regulators

, LTC and LT are registered trademarks of Linear Technology Corporation.

OPTI-LOOP and PolyPhase are trademarks of Linear Technology Corporation.

The LTC

1629/LTC1629-PG are multiple phase, dual,

synchronous step-down current mode switching regula-

tor controllers that drive 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-PG includes a power good output pin that re-

places the AMPMD control pin of the LTC1629.

Figure 1. High Current Dual Phase Step-Down Converter

■

Desktop Computers

■

Internet Servers

■

Large Memory Arrays

■

DC Power Distribution Systems

■

Dual Controller Operates from One to Twelve Phases

■

Reduces Required Input Capacitance and Power

Supply Induced Noise

■

Current Mode Control Ensures Current Sharing

■

Phase-Lockable Fixed Frequency: 150kHz to 300kHz

■

1.8MHz Effective Switching Frequency

■

True Remote Sensing Differential Amplifier

■

OPTI-LOOP

Compensation Reduces C

OUT

■

1% Output Voltage Accuracy

■

Power Good Output Voltage Monitor (LTC1629-PG)

■

Wide V

Range: 4V to 36V Operation

■

Very Low Dropout Operation: 99% Duty Cycle

■

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

■

Micropower Shutdown

■

Available in 28-Lead SSOP Package

1629 TA01

TG1

BOOST1

SW1

BG1

PGND

SENSE1

–

TG2

BOOST2

SW2

BG2

INTV

SENSE2

–

RUN/SS

EAIN

DIFFOUT

–

LTC1629-PG

SGND

0.1µF

PGOOD

0.1µF

16k

1000pF

10Ω

3.3k

16k

10µF ×4

35V

CERAMIC

OUT

1000µF ×2

L1, L2: CEPH149-IROMCC

OUT

: T510E108K004AS

D1, D2: UP5840

M1, M3: IRF7811

M2, M4: IRF7809

OUT

1.6V/40A

1µH

0.003Ω

5V TO 28V

1µH

×2

0.47µF

10µF

0.003Ω

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

Summary of content (28 pages)

PAGE 1
LTC1629/LTC1629-PG PolyPhase, High Efficiency, Synchronous Step-Down Switching Regulators U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Dual Controller Operates from One to Twelve Phases Reduces Required Input Capacitance and Power Supply Induced Noise Current Mode Control Ensures Current Sharing Phase-Lockable Fixed Frequency: 150kHz to 300kHz 1.
PAGE 2
LTC1629/LTC1629-PG 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, AMPMD, PGOOD Voltages ............7V to – 0.3V Boosted Driver Voltage (BOOST-SW) .........
PAGE 3
LTC1629/LTC1629-PG 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 ISENSE Total Sense Pins Source Current Each Channel; VSENSE1 –, 2 – = VSENSE1+, 2 + = 0V – 85 – 60 µA DFMAX Maximum Duty Factor In Dropout 98 99.
PAGE 4
LTC1629/LTC1629-PG ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VRUN/SS1, 2 = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage Op Amp Mode; VCM = 2.5V; LTC1629 Only VDIFFOUT = 5V; IDIFFOUT = 1mA MIN TYP MAX IB Input Bias Current Op Amp Mode; LTC1629 Only AOL Open Loop DC Gain Op Amp Mode; 0.
PAGE 5
LTC1629/LTC1629-PG U W TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Input Voltage and Mode 1000 250 600 ON 400 200 5.05 INTVCC AND EXTVCC SWITCH VOLTAGE (V) EXTVCC VOLTAGE DROP (mV) 800 SUPPLY CURRENT (µA) INTVCC and EXTVCC Switch Voltage vs Temperature EXTVCC Voltage Drop 200 LTC1629 150 LTC1629-PG 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/LTC1629-PG 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 –0.4 1 0 3 2 LOAD CURRENT (A) 0 4 5 0 1 2 3 4 5 –100 6 VRUN/SS (V) 2 0 4 1629 G14 1629 G13 Maximum Current Sense Threshold vs Temperature 1629 G15 RUN/SS Current vs Temperature 80 1.8 78 1.
PAGE 7
LTC1629/LTC1629-PG U W TYPICAL PERFOR A CE CHARACTERISTICS Current Sense Pin Input Current vs Temperature EXTVCC Switch Resistance vs Temperature 10 350 VOUT = 5V VFREQSET = 5V 33 31 29 27 25 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 300 8 LTC1629 6 4 LTC1629-PG VFREQSET = OPEN 200 VFREQSET = 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 Te
PAGE 8
LTC1629/LTC1629-PG 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.
PAGE 9
LTC1629/LTC1629-PG W FU CTIO AL DIAGRA U U LTC1629-PG PGOOD CONNECTION DIFFOUT PGOOD VOS – – 0.86V + A1 VOS + EAIN – – + + 0.
PAGE 10
LTC1629/LTC1629-PG U OPERATIO (Refer to Functional Diagram) Main Control Loop Low Current Operation The LTC1629 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.
PAGE 11
LTC1629/LTC1629-PG U OPERATIO (Refer to Functional Diagram) INTVCC/EXTVCC Power 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.
PAGE 12
LTC1629/LTC1629-PG 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 current comparator has a maximum threshold of 75mV/RSENSE and an input common mode range of SGND to 1.5( 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.
PAGE 13
LTC1629/LTC1629-PG 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.
PAGE 14
LTC1629/LTC1629-PG 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.
PAGE 15
LTC1629/LTC1629-PG 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.
PAGE 16
LTC1629/LTC1629-PG 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 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.
PAGE 17
LTC1629/LTC1629-PG U W U U APPLICATIO S I FOR ATIO OPTIONAL EXTVCC CONNECTION 5V < VSEC < 7V + CIN + VIN VIN LTC1629 VIN 1N4148 TG1 EXTVCC 6.8V N-CH VSEC N-CH LTC1629 1µF T1 BAT85 0.22µF BAT85 BAT85 VN2222LL EXTVCC RSENSE VOUT SW1 COUT BG1 VOUT L1 + + BG1 + CIN TG1 + RSENSE SW1 VIN CIN COUT N-CH N-CH PGND PGND 1629 F05b 1629 F05a Figure 5a. Secondary Output Loop and EXTVCC Connection Figure 5b. Capacitive Charge Pump for EXTVCC source of the desired MOSFET.
PAGE 18
LTC1629/LTC1629-PG U W U U APPLICATIO S I FOR ATIO rent thus ramps up slowly, reducing the starting surge 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 is put into low current shutdown (IQ < 40µA).
PAGE 19
LTC1629/LTC1629-PG 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 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.
PAGE 20
LTC1629/LTC1629-PG 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.
PAGE 21
LTC1629/LTC1629-PG 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.
PAGE 22
LTC1629/LTC1629-PG U U W U APPLICATIO S I FOR ATIO Although the LTC1629 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 1.8 V   = 10k   = 30k  2.4V − 1.
PAGE 23
LTC1629/LTC1629-PG 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%.
PAGE 24
LTC1629/LTC1629-PG 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.
PAGE 25
LTC1629/LTC1629-PG 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).
PAGE 26
LTC1629/LTC1629-PG U TYPICAL APPLICATIO S OPTIONAL SYNC CLOCK IN L1 2 0.33µF 3 8.06k, 1% 4 5 6 0.33µF 100pF 47k 6800pF 25.5k, 1% 8 9 10 11 12 470pF 13 14 CLKOUT SENSE1 + TG1 SENSE1 – SW1 EAIN BOOST1 PLLFLTR PLLIN LTC1629 VIN BG1 PHASMD EXTVCC ITH INTVCC SGND PGND VDIFFOUT BG2 VOS – BOOST2 + SW2 VOS SENSE2 – TG2 SENSE2 + AMPMD 27 0.47µF 26 25 M1 D7 24 21 1µF,25V 20 22µF 6.3V 2X150µF 16V GND 3X470µF, 6.3V KEMET CAP VOUT1 3.3V/90A 19 18 17 D8 16 0.
PAGE 27
LTC1629/LTC1629-PG U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. G Package 28-Lead Plastic SSOP (0.209) (LTC DWG # 05-08-1640) 10.07 – 10.33* (0.397 – 0.407) 28 27 26 25 24 23 22 21 20 19 18 17 16 15 7.65 – 7.90 (0.301 – 0.311) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 5.20 – 5.38** (0.205 – 0.212) 1.73 – 1.99 (0.068 – 0.078) 0° – 8° 0.13 – 0.22 (0.005 – 0.009) 0.55 – 0.95 (0.022 – 0.037) NOTE: DIMENSIONS ARE IN MILLIMETERS *DIMENSIONS DO NOT INCLUDE MOLD FLASH.
PAGE 28
LTC1629/LTC1629-PG U TYPICAL APPLICATIO L1 0.1µF 1 2 17.8k 3 10k 4 5 13.2k 6 1000pF 7 8 9 16.5k 10 11 12 100pF 13 14 CLKOUT SENSE1 + TG1 SENSE1 – SW1 EAIN BOOST1 PLLFLTR VIN BG1 PLLIN PHASMD EXTVCC ITH INTVCC SGND LTC1629-PG 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.