Datasheet

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LTC3425

3425f

FEATURES

APPLICATIO S

DESCRIPTIO

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Handheld Computers

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Point-of-Load Regulators

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3.3V to 5V Conversion

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

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High Efficiency: Up to 95%

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Up to 3A Continuous Output Current

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4-Phase Operation for Low Output Ripple

and Tiny Solution Size

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Output Disconnect and Inrush Current Limiting

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Very Low Quiescent Current: 12µA

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0.5V to 4.5V Input Range

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2.4V to 5.25V Adjustable Output Voltage

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Adjustable Current Limit

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Adjustable, Fixed Frequency Operation from

100kHz to 2MHz per Phase

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Synchronizable Oscillator with Sync Output

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Internal Synchronous Rectifiers

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Manual or Automatic Burst Mode

Operation

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Power Good Comparator

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<1µA Shutdown Current

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Antiringing Control

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5mm × 5mm Thermally Enhanced QFN Package

5A, 8MHz, 4-Phase

Synchronous Step-Up

DC/DC Converter

Burst Mode is a registered trademark of Linear Technology Corporation.

The LTC

3425 is a synchronous, 4-phase boost converter

with output disconnect capable of operation below 1V

input. It includes four N-channel MOSFET switches and

four P-channel synchronous rectifiers for an effective

DS(ON)

of 0.045Ω and 0.05Ω, respectively. 4-phase

operation greatly reduces peak inductor currents, and

capacitor ripple current, and increases effective switching

frequency, minimizing inductor and capacitor sizes. True

output disconnect eliminates inrush current and allows

zero load current in shutdown. External Schottky diodes

are not required in most applications (V

OUT

< 4.3V). Power

saving Burst Mode operation can be user controlled or left

in automatic mode.

Other features include 1µA shutdown current, program-

mable frequency with sync in and out, programmable

soft-start, antiringing control, thermal shutdown, adjust-

able current limit, reference output and power good

comparator.

The LTC3425 is available in a small, thermally enhanced

32-pin QFN package.

2.7µH

2.2µF

0.01µF

75k

15k

20k

2.7µH 2.7µH 2.7µH

: TAIYO YUDEN JMK107BJ225MA

OUT

: TAIYO YUDEN JMK212BJ475MG (×4)

L1-L4: TDK RLF5018T-2R7M1R8

SWA

2V TO 3V

SWB

LTC3425

SWC SWD

SGND

SHDN

OFF ON

OUTS

OUTA

OUTB

OUTC

OUTD

REFOUT

CCM

REFEN

SYNCIN

BURST

LIM

PGOOD

SYNCOUT

COMP

GNDA GNDB GNDC GNDD

330pF

22pF

3425 TA01

4.7µF

×4

0.01µF

33k

590k

1M 10k

OUT

3.3V

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

1 10 100 1000 10000

3425 TA02

100

= 2.4V

OUT

= 3.3V

f = 1MHz/PHASE

L = 2.7µH

Burst Mode

OPERATION

FIXED

FREQUENCY

MODE

TYPICAL APPLICATIO

Summary of content (24 pages)

PAGE 1
LTC3425 5A, 8MHz, 4-Phase Synchronous Step-Up DC/DC Converter DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®3425 is a synchronous, 4-phase boost converter with output disconnect capable of operation below 1V input. It includes four N-channel MOSFET switches and four P-channel synchronous rectifiers for an effective RDS(ON) of 0.045Ω and 0.05Ω, respectively.
PAGE 2
LTC3425 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO VIN Voltage ................................................. – 0.3V to 6V SWA-D Voltages ..........................................– 0.3V to 6V VOUTA-D, VOUTS Voltages............................ – 0.3V to 6V BURST, SHDN, SS, REFEN, SYNCOUT, PGOOD, REFOUT, CCM, SYNCIN Voltages ............... – 0.3V to 6V Operating Ambient Temperature Range (Note 5) ..............................................
PAGE 3
LTC3425 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V, RT = 15k, unless otherwise noted. PARAMETER CONDITIONS PMOS Turn-Off Current CCM < 0.4V MIN –80 mA PMOS Reverse Current Limit CCM > 1.4V 0.6 A Max Duty Cycle ● Min Duty Cycle ● 83 Frequency Accuracy RT = 15k ● 0.8 SHDN Input High VOUT = 0V (Initial Start-Up) VOUT > 2.4V ● ● 1 0.
PAGE 4
LTC3425 U W TYPICAL PERFOR A CE CHARACTERISTICS SWA, SWB, SWC, SWD at 1MHz/Phase SW Pin and Oscillator SYNCOUT IL 0.2A/DIV SWA 2V/DIV SWA TO SWD 5V/DIV SYNCOUT 2V/DIV 250ns/DIV SW Pin and Inductor Current in Discontinous Mode. Antiring Circuit Eliminates High Frequency Ringing SW 2V/DIV 250ns/DIV 3425 G01 VIN = 2.4V VOUT = 3.3V COUT = 220µF 3425 G02 3425 G03 Output Voltage Ripple at 2.5A Load with a 47µF Ceramic Bulk Capacitor Output Voltage Ripple at 2.5A Load with Only Four 4.
PAGE 5
LTC3425 U W TYPICAL PERFOR A CE CHARACTERISTICS Converter Efficiency for VOUT = 3.3V 100 98 100 80 80 VIN = 1.2V 70 EFFICIENCY (%) VIN = 2.4V 60 VIN = 1.2V 50 40 30 TA = 25°C 96 VIN = 2.4V VOUT = 3.3V 94 1MHz/PHASE VIN = 3.3V 90 VIN = 2.4V 70 VIN = 3.3V 60 EFFICIENCY (%) VIN = 2.4V 90 VIN = 2.4V 50 40 30 20 Burst Mode OPERATION 1MHz/PHASE TA = 25°C 0 0.1 1 10 100 1000 OUTPUT CURRENT (mA) TA = 25°C 0 0.
PAGE 6
LTC3425 U W TYPICAL PERFOR A CE CHARACTERISTICS Maximum Output Current in Burst Mode Operation 350 0.7 TA = 25°C 100 TA = 25°C VOUT = 3.3V 250 VOUT = 5V 200 150 100 0.5 0.4 VOUT = 5V 0.3 0.2 0.1 50 0 0.9 0 1 2 1.5 2.5 3 3.5 4 4.5 5 1.0 1.1 VIN (V) 1.2 1.3 VIN (V) 1.4 1.5 Shutdown Voltage vs Temperature VIN > 2.3V LEAVE Burst Mode OPERATION 70 ENTER Burst Mode OPERATION VOUT = 3.3V 0.425 SHUTDOWN VOLTAGE (V) SS CHARGE CURRENT (µA) VOUT = 3.3V 2.0 1.5 VIN < 2.
PAGE 7
LTC3425 U W TYPICAL PERFOR A CE CHARACTERISTICS Peak Current Limit vs Temperature 3 1.225 2 PEAK ILIM (NORMALIZED) (%) 1.230 1.215 1.210 1.205 15 35 55 75 TEMPERATURE (°C) 95 115 2.0 1 0 –1 –2 –3 –45 –25 –5 15 35 55 75 TEMPERATURE (°C) 3425 G29 95 115 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 –45 –25 –5 15 35 55 75 TEMPERATURE (°C) 3425 G30 Burst Mode VOUT Quiescent Current vs Temperature 95 115 3425 G31 Error Amplifier gm vs Temperature 20 55 15 50 gm (µS) 1.
PAGE 8
LTC3425 U U U PI FU CTIO S GNDA–D (Pins 1, 2, 7, 8, 17, 18, 23, 24): Power Ground for the IC and the Four Internal N-channel MOSFETs. Connect directly to the power ground plane. SWA–D (Pins 3, 6, 19, 22): Switch Pins. Connect inductors here. Minimize trace length to keep EMI to a minimum. For discontinuous inductor current, a controlled impedance is internally connected from SW to VIN to minimize EMI. For applications where VOUT > 4.
PAGE 9
LTC3425 U U U PI FU CTIO S ILIM (Pin 27): Current Limit Adjust Pin. Connect a resistor from ILIM to SGND to set the peak current limit threshold for the N-channel MOSFETs, according to the formula (note that this is the peak current in each inductor): ILIM = 130 R VOUT 2 where I is in Amps and R is in kΩ. Do not use values less than 75k.
PAGE 10
LTC3425 W BLOCK DIAGRA 1V TO 4.5V + 29 3 VIN FB 6 SWA 1 OF 4 SWB 19 22 SWC SWD VOUTA 4 VOUTB 5 + ANTIRING 0.8V – PMOS ENABLE PWM LOGIC AND DRIVERS MODE CONTROL 26 VOUTC 20 P CCM VOUTD 21 + – VOUT 2.5V TO 5.25V N I/2000 ZERO DIVIDER 4-PHASE GEN 28 SYNC 30 RT 4 + CLK SLOPE 4 IOSC OSC Σ VOUTS 10 + Σ + – – + + 1.086/ 1.116 + PGOOD 16 – SYNCIN 4 4 4 + + 1.22V MODE 25 Burst Mode CONTROL SYNCOUT – BURST COMP 0.
PAGE 11
LTC3425 U OPERATIO DETAILED DESCRIPTION OUTPUT RIPPLE CURRENT (A) The LTC3425 provides high efficiency, low noise power for high current boost applications such as cellular phones and PDAs. The true output disconnect feature eliminates inrush current and allows VOUT to go to zero during shutdown. The current mode architecture with adaptive slope compensation provides ease of loop compensation with excellent transient load response.
PAGE 12
LTC3425 U OPERATIO SWITCH A VOLTAGE SWITCH B VOLTAGE SWITCH C VOLTAGE SWITCH D VOLTAGE INDUCTOR A CURRENT INDUCTOR B CURRENT INDUCTOR C CURRENT INDUCTOR D CURRENT INPUT CURRENT RECTIFIER A CURRENT RECTIFIER B CURRENT RECTIFIER C CURRENT RECTIFIER D CURRENT OUTPUT RIPPLE CURRENT 3425 F02 Figure 2.
PAGE 13
LTC3425 U OPERATIO SWITCH A VOLTAGE SWITCH B VOLTAGE SWITCH C VOLTAGE SWITCH D VOLTAGE INDUCTOR A CURRENT INDUCTOR B CURRENT INDUCTOR C CURRENT INDUCTOR D CURRENT INPUT CURRENT RECTIFIER A CURRENT RECTIFIER B CURRENT RECTIFIER C CURRENT RECTIFIER D CURRENT OUTPUT RIPPLE CURRENT 3432 F03 Figure 3. Simplified Voltage and Current Waveforms for 4-Phase Operation at 75% Duty Cycle internally controlled. The device can start up under some load (see the graph Start-Up Current vs Input Voltage).
PAGE 14
LTC3425 U OPERATIO EFFICIENCY (%) 98 60 RT TA = 25°C 96 VIN = 2.4V VOUT = 3.3V 94 1MHz/PHASE fOSC = 92 fSWITCH = 90 4 PHASE 88 where fOSC is in MHz and RT is in kΩ. 86 2 PHASE 3 PHASE 84 82 80 100 fOSC 15 = 4 RT 1000 LOAD (mA) 10000 3425 G13 Figure 4. LTC3425 Efficiency vs Load for 2-, 3- and 4-Phase Operation Low Noise Fixed Frequency Operation Shutdown: The part is shut down by pulling SHDN below 0.25V and made active by pulling the pin above 1V.
PAGE 15
LTC3425 U OPERATIO Current Limit: The programmable current limit circuit sets the maximum peak current in the NMOS switches. The current limit level is programmed using a resistor to ground on the ILIM pin. Do not use values below 75k. In Burst Mode operation, the current limit is automatically set to a nominal value of 0.6A peak for optimal efficiency. ILIM = 130 per Phase R where I is in Amps and R is in kΩ.
PAGE 16
LTC3425 U OPERATIO a heavy load is suddenly applied to the converter after being in Burst Mode operation for an extended period of time. For automatic operation, an RC network should be connected from BURST to ground. The value of the resistor will control the average load current (IBURST) at which Burst Mode operation will be entered and exited (there is hysteresis to prevent oscillation between modes).
PAGE 17
LTC3425 U W U U APPLICATIO S I FOR ATIO L1 The inductor current ripple is typically set to 20% to 40% of the maximum inductor current. RT CIN CSS L4 COUT For high efficiency, choose an inductor with high frequency core material, such as ferrite to reduce core loses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses, and must be able to handle the peak inductor current without saturating. To minimize radiated noise, use a shielded inductor.
PAGE 18
LTC3425 U W U U APPLICATIO S I FOR ATIO The ESR (equivalent series resistance) is usually the most dominant factor for ripple in most power converters. The ripple due to capacitor ESR is given by: VRCESR = IP • CESR where CESR = Capacitor Series Resistance The ESL (equivalent series inductance) is also an important factor for high frequency converters. Using small, surface mount ceramic capacitors, placed as close as possible to the VOUT pins, will minimize ESL.
PAGE 19
LTC3425 U W U U APPLICATIO S I FOR ATIO VIN 3.3V CIN 2.2µF L1 2.7µH L2 2.7µH L3 2.7µH L4 2.7µH D1 CS 0.47µF ×2 D2 D3 D4 VIN SWA SWB SWC SHDN REFOUT CCM REFEN SWD VOUTS VOUTA VOUTB VOUTC VOUTD Q1 COUT 4.7µF ×4 LTC3425 SYNCIN BURST VOUT RT RT 12.1k ILIM RLIM 75k SGND GNDA GNDB FB COMP SS SYNCOUT PGOOD GNDC GNDD R2 309k R4 100k CBULK 150µF 6.3V VOUT 5V 2.5A R1 100k C2 220pF CSS 0.
PAGE 20
LTC3425 U W U U APPLICATIO S I FOR ATIO modulator control to output DC gain, and the error amp open-loop gain gives the DC gain of the system: G DC = G CONTROLOUTPUT • G EA • G CONTROL = VREF VOUT 8 • VIN , G EA ≈ 5, 000 IOUT The output filter pole is given by: IOUT π • VOUT • COUT where COUT is the output filter capacitor. The output filter zero is given by: FFILTERPOLE = FFILTERZERO = 1 2 • π • RESR • COUT where RESR is the output capacitor equivalent series resistance.
PAGE 21
LTC3425 U TYPICAL APPLICATIO S Single or Dual Cell to 3.3V Boost with Automatic Burst Mode Operation VIN = 1.1V TO 3V + CIN 2.2µF L1 2.2µH VIN SWA L2 2.2µH SWB SHDN REFOUT CCM REFEN L3 2.2µH SWC L4 2.2µH SWD VOUTS VOUTA VOUTB VOUTC VOUTD R5 10k C1 22pF COUT 4.7µF ×4 LTC3425 SYNCIN BURST C3 0.056µF R4 20k RT RT 15k RLIM 75k ILIM SGND GNDA GNDB FB COMP SS SYNCOUT PGOOD GNDC GNDD R5 100k + CBULK 150µF 4V R1 301k C2 220pF CSS 0.01µF R2 511k VOUT 3.
PAGE 22
LTC3425 U TYPICAL APPLICATIO S Application with User Commanded Burst Mode Operation and Buffered Reference Output Enabled VIN = 1.8V TO 3V + CIN 2.2µF L1 3.3µH VIN SWA L2 3.3µH SWB SHDN REFOUT VREF C1 0.1µF CCM VOUT REFEN L3 3.3µH SWC L4 3.3µH SWD VOUTS VOUTA VOUTB VOUTC VOUTD R4 10k C3 22pF COUT 4.7µF ×4 LTC3425 SYNCIN BURST PWM BURST RT RT 30.
PAGE 23
LTC3425 U PACKAGE DESCRIPTIO UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693) 0.57 ±0.05 5.35 ±0.05 4.20 ±0.05 3.45 ±0.05 (4 SIDES) PACKAGE OUTLINE 0.23 ± 0.05 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 5.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 ± 0.05 0.00 – 0.05 0.40 ± 0.10 31 32 PIN 1 TOP MARK 1 2 3.45 ± 0.10 (4-SIDES) (UH) QFN 0102 0.200 REF NOTE: 1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE M0-220 VARIATION WHHD-(X) (TO BE APPROVED) 2.
PAGE 24
LTC3425 U TYPICAL APPLICATIO 10MHz, High Current, Very Low Profile, 8-Phase Converter Using Two LTC3425s Operating in Fixed Frequency Mode with Forced CCM (Max Component Height = 1.6mm) VIN 2.5V CIN1 2.2µF L1 1µH VIN SWA L2 1µH SWB SHDN REFOUT CCM VOUT REFEN L3 1µH SWC SWD VOUTS VOUTA VOUTB VOUTC VOUTD LTC3425 SYNCIN BURST RT RT1 12.1k ILIM R5 75k SGND GNDA GNDB CIN2 2.2µF L4 1µH VIN L5 1µH SWA L6 1µH SWB SHDN REFOUT COUT1 4.