Datasheet

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LTC3374

3374fa

For more information www.linear.com/LTC3374

Typical applicaTion

FeaTures DescripTion

8-Channel Parallelable

1A Buck DC/DCs

The LT C

3374 is a high efficiency multioutput power sup-

ply IC. The DC/DCs consist of eight synchronous buck

converters

(1A each) all powered from independent 2.25V

to 5.5V input supplies.

The DC/DCs may be used independently or in parallel to

achieve higher currents of up to 4A per output with a shared

inductor. The common buck switching frequency may be

programmed with an external resistor, synchronized to an

external oscillator, or set to a default internal 2MHz clock.

The operating mode for all DC/DCs may be programmed

via the MODE pin.

To reduce input noise the buck converters are phased in

90° steps. Precision enable pin thresholds provide reli

able power-up sequencing. The LTC3374 is available in a

compact 38-lead 5mm × 7mm QFN package as well as a

38-lead TSSOP package.

8-Channel 1A Multioutput Buck Regulator

Buck Efficiency vs I

LOAD

applicaTions

8-Channel Independent Step-Down DC/DCs

Master-Slave Configurable for Up to 4A per Output

Rail with a Single Inductor

Independent V

Supplies for Each DC/DC

(2.25V to 5.5V)

All DC/DCs Have 0.8V to V

Output Range

Precision Enable Pin Thresholds for Autonomous

Sequencing

1MHz to 3MHz Programmable/Synchronizable

Oscillator Frequency (2MHz Default)

Die Temperature Monitor Output

Thermally Enhanced 38-Lead QFN (5mm × 7mm)

and TSSOP Packages

General Purpose Multichannel Power Supplies

Industrial/Automotive/Communications

L, LT , LT C , LT M, Linear Technology, the Linear logo and Burst Mode are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

0.8V TO V

IN1

UP TO 1A

BUCK1

2.7V TO 5.5V

IN1

BUCK2

IN2

BUCK7

IN7

BUCK8

IN8

0.8V TO V

IN2

UP TO 1A

SLAVE

MASTER

SLAVE

MASTER

SLAVE

MASTER

EN1

EN2

EN3

EN4

EN5

EN6

EN7

EN8

PGOOD_ALL

TEMP

MODE

SYNC

0.8V TO V

IN7

UP TO 1A

0.8V TO V

IN8

UP TO 1A

LTC3374

3374 TA01a

•

LOAD CURRENT (mA)

EFFICIENCY (%)

100

1000

2000

3374 TA01b

3000

4000

FORCED CONTINUOUS MODE

= 3.3V, V

OUT

= 1.8V

OSC

= 1MHz, L = 3.3µH

SINGLE BUCK

DUAL BUCK

TRIPLE BUCK

QUAD BUCK

Summary of content (26 pages)

PAGE 1
LTC3374 8-Channel Parallelable 1A Buck DC/DCs Features n n n n n n n n Description 8-Channel Independent Step-Down DC/DCs Master-Slave Configurable for Up to 4A per Output Rail with a Single Inductor Independent VIN Supplies for Each DC/DC (2.25V to 5.5V) All DC/DCs Have 0.
PAGE 2
LTC3374 Table of Contents Features...................................................... 1 Applications................................................. 1 Typical Application ......................................... 1 Description.................................................. 1 Absolute Maximum Ratings............................... 3 Pin Configuration........................................... 3 Order Information........................................... 3 Electrical Characteristics...................
PAGE 3
LTC3374 Absolute Maximum Ratings (Note 1) VIN1-8, FB1-8, EN1-8, VCC, PGOOD_ALL, SYNC, RT, MODE.......................................... –0.3V to 6V TEMP................... –0.3V to Lesser of (VCC + 0.3V) or 6V IPGOOD_ALL................................................................5mA Operating Junction Temperature Range (Notes 2, 3)............................................. –40°C to 150°C Storage Temperature Range...................
PAGE 4
LTC3374 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified.
PAGE 5
LTC3374 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Interface Logic Pins (PBGOOD_ALL, MODE) IOH Output High Leakage Current PGOOD_ALL 5.5V at Pin –1 VOL Output Low Voltage PGOOD_ALL 3mA into Pin VIH Input High Threshold MODE l VIL Input Low Threshold MODE l 1 0.
PAGE 6
LTC3374 Typical Performance Characteristics Buck VIN Undervoltage Threshold vs Temperature 2.30 2.65 2.25 2.60 VCC RISING 2.55 2.50 VCC FALLING 2.45 60 ALL REGULATORS 55 IN SHUTDOWN 50 2.20 VIN RISING 2.15 2.10 VIN FALLING 2.05 2.40 2.30 –50 –25 1.90 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 25 50 75 100 125 150 TEMPERATURE (°C) fOSC (MHz) IVCC (µA) 240 VCC = 3.3V 200 VCC = 2.7V 160 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 –50 –25 0 VCC = 5.5V VCC = 3.3V VCC = 2.
PAGE 7
LTC3374 Typical Performance Characteristics VCC = 3.3V 3.5 1200 3.0 1000 2.5 800 VTEMP (mV) 2.0 1.5 Enable Threshold vs Temperature 900 850 400 ACTUAL VTEMP 200 0.5 0 –200 EN FALLING 600 550 450 IDEAL VTEMP 0 50 415 20 40 60 80 100 120 TEMPERATURE (°C) 400 –50 –25 140 0 25 50 75 100 125 150 TEMPERATURE (°C) 3374 G11 Buck VIN Supply Current vs Temperature 550 Burst Mode OPERATION FB = 850mV 40 IVIN_BURST (µA) 410 405 EN RISING EN FALLING 390 30 VIN = 5.5V 20 VIN = 2.
PAGE 8
LTC3374 Typical Performance Characteristics 550 500 500 VIN = 2.25V 400 VIN = 3.3V 350 VIN = 5.5V 300 100 80 450 VIN = 2.25V 400 VIN = 3.3V 350 300 250 0 1A Buck Efficiency vs ILOAD 2A Buck Efficiency vs ILOAD 20 10 1 10 100 LOAD CURRENT (mA) 90 70 FORCED CONTINUOUS MODE 60 50 40 VOUT = 1.8V fOSC = 2MHz L = 2.2µH VIN = 2.25V VIN = 3.3V VIN = 5.5V 30 20 10 0 1000 10 100 LOAD CURRENT (mA) 1 3A Buck Efficiency vs ILOAD 50 40 VOUT = 2.5V fOSC = 2MHz L = 2.2µH VIN = 2.7V VIN = 3.
PAGE 9
LTC3374 Typical Performance Characteristics 1A Buck Efficiency vs Frequency (Forced Continuous Mode) 4A Buck Efficiency vs ILOAD 100 100 100 90 90 90 80 80 60 50 VOUT = 1.8V fOSC = 2MHz L = 2.2µH VIN = 2.25V VIN = 3.3V VIN = 5.5V 20 10 0 1 60 FORCED CONTINUOUS MODE 50 40 VOUT = 2.5V fOSC = 2MHz L = 2.2µH VIN = 2.7V VIN = 3.3V VIN = 5.5V 30 20 10 0 10 100 1000 LOAD CURRENT (mA) 3374 G25 70 EFFICIENCY (%) IL = 20mA 60 50 40 VOUT = 1.8V VIN = 3.3V fOSC = 2MHz L = 3.3µH 1 1.2 1.4 1.6 1.
PAGE 10
LTC3374 Typical Performance Characteristics 4A Buck Regulator No-Load Start-Up Transient (Forced Continuous Mode) 1A Buck Regulator No-Load Start-Up Transient (Burst Mode Operation) VOUT 500mV/DIV INDUCTOR CURRENT 500mA/DIV EN 2V/DIV VOUT 500mV/DIV VOUT 100mV/DIV AC-COUPLED INDUCTOR CURRENT 500mA/DIV INDUCTOR CURRENT 200mA/DIV 0mA EN 2V/DIV VIN = 3.3V 200µs/DIV 3374 G33 VIN = 3.
PAGE 11
LTC3374 Pin Functions (QFN/TSSOP) FB1 (Pin 1/Pin 4): Buck Regulator 1 Feedback Pin. Receives feedback by a resistor divider connected across the output. VIN1 (Pin 2/Pin 5): Buck Regulator 1 Input Supply. Bypass to GND with a 10µF or larger ceramic capacitor. SW1 (Pin 3/Pin 6): Buck Regulator 1 Switch Node. External inductor connects to this pin. SW2 (Pin 4/Pin 7): Buck Regulator 2 Switch Node. External inductor connects to this pin. VIN2 (Pin 5/Pin 8): Buck Regulator 2 Input Supply.
PAGE 12
LTC3374 Pin Functions (QFN/TSSOP) VIN5 (Pin 21/Pin 24): Buck Regulator 5 Input Supply. Bypass to GND with a 10µF or larger ceramic capacitor. May be driven by an independent supply or must be shorted to VIN4 when buck regulator 5 is combined with buck regulator 4 for higher current. VIN8 (Pin 30/Pin 33): Buck Regulator 8 Input Supply. Bypass to GND with a 10µF or larger ceramic capacitor.
PAGE 13
LTC3374 Block Diagram (Pin numbers reflect QFN package) TOP LOGIC VCC 35 15 PGOOD_ALL SYNC 16 REF, CLK RT 17 8 PGOOD TEMP 36 BANDGAP, OSCILLATOR, UV, OT TEMP MONITOR 34 MODE 30 VIN8 VIN1 2 SW1 3 FB1 1 BUCK REGULATOR 1 1A BUCK REGULATOR 8 1A MASTER/SLAVE LINES MASTER/SLAVE LINES 27 VIN7 VIN2 5 FB2 6 BUCK REGULATOR 2 1A BUCK REGULATOR 7 1A MASTER/SLAVE LINES 24 VIN6 BUCK REGULATOR 3 1A BUCK REGULATOR 6 1A MASTER/SLAVE LINES 25 FB6 MASTER/SLAVE LINES 21 VIN5 VIN4 11 FB4 12 23 SW6 1
PAGE 14
LTC3374 Operation Buck Switching Regulators The LTC3374 contains eight monolithic 1A synchronous buck switching regulators. All of the switching regulators are internally compensated and need only external feedback resistors to set the output voltage. The switching regulators offer two operating modes: Burst Mode operation (when the MODE pin is set low) for higher efficiency at light loads and forced continuous PWM mode (when the MODE pin is set high) for lower noise at light loads.
PAGE 15
LTC3374 Operation operation of the combined bucks; the enable of the slave regulator (EN2) must be tied to ground. Any combination of 2, 3, or 4 adjacent buck regulators may be combined to provide either 2A, 3A, or 4A of average output load current. For example, buck regulator 1 and buck regulator 2 may run independently, while buck regulators 3 and 4 may be combined to provide 2A, while buck regulators 5 through 8 may be combined to provide 4A.
PAGE 16
LTC3374 Operation The LTC3374’s internal oscillator can be synchronized through an internal PLL circuit, to an external frequency by applying a square wave clock signal to the SYNC pin. During synchronization, the top MOSFET turn-on of buck switching regulators 1 and 2 are locked to the rising edge of the external frequency source. All other buck switching regulators are locked to the appropriate phase of the external frequency source (see Buck Switching Regulators).
PAGE 17
LTC3374 Applications Information Buck Switching Regulator Output Voltage and Feedback Network Combined Buck Regulators The output voltage of the buck switching regulators is programmed by a resistor divider connected from the switching regulator’s output to its feedback pin and is given by VOUT = VFB(1 + R2/R1) as shown in Figure 2. Typical values for R1 range from 40k to 1M.
PAGE 18
LTC3374 Applications Information Table 1. Recommended Inductors for 1A Buck Regulators PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) 1.0 3 38 3 × 3.6 × 1.2 1239AS-H-1R0N 1 2.5 65 2.5 × 2.0 × 1.2 XFL4020-222ME 2.2 3.5 23.5 4 × 4 × 2.1 1277AS-H-2R2N 2.2 2.6 84 3.2 × 2.5 × 1.2 IHLP1212BZER2R2M-11 2.2 3 46 3 × 3.6 × 1.2 XFL4020-332ME 3.3 2.8 38.3 4 × 4 × 2.1 IHLP1212BZER3R3M-11 3.3 2.7 61 3 × 3.6 × 1.
PAGE 19
LTC3374 Applications Information PCB Considerations When laying out the printed circuit board, the following list should be followed to ensure proper operation of the LTC3374: 1. The exposed pad of the package (Pin 39) should connect directly to a large ground plane to minimize thermal and electrical impedance. 2. All the input supply pins should each have a decoupling capacitor. 3.
PAGE 20
LTC3374 Applications Information 3.3V TO 5.5V 10µF 3.3V 1A 2.2µH 22µF VIN8 VIN1 SW1 SW8 FB1 FB8 1.02M 806k 324k 3.0V TO 5.5V 10µF 3.0V 1A 2.2µH 22µF 2.25V TO 5.5V 2.2µH 22µF 1.8V 1A 10µF 1.5V 1A 10µF 1.2V 1A 10µF 1.0V 1A 10µF 649k VIN2 VIN7 SW2 SW7 FB2 FB7 2.25V TO 5.5V 2.2µH 1.0M 715k 365k 22µF 806k LTC3374 2.5V TO 5.5V 10µF 2.5V 1A 2.2µH 22µF VIN3 VIN6 SW3 SW6 FB3 FB6 1.02M 232k 475k 2.25V TO 5.5V 10µF 2.0V 1A 2.2µH 22µF VIN4 VIN5 SW4 SW5 FB4 FB5 2.
PAGE 21
LTC3374 Applications Information VIN 5.5V TO 36V CIN 22µF 100k INTVCC VIN INTVCC 2.2µF PGOOD PLLIN/MODE LTC2955TS8-1 VIN EN KILL INT PB MICROPROCESSOR CONTROL ILIM PGND 470pF FREQ 34.8k 0.1µF 1M ITH SENSE+ – TRACK/SS SENSE EXTVCC SGND VFB 22µF 2.5V 1A 22µF 5V 6A 100k MTOP, MBOT: Si7850DP L1 COILCRAFT SER1360-802KL COUT: SANYO 10TPE330M D1: DFLS1100 19.1k VIN8 SW1 SW8 FB1 FB8 10µF 2.2µH 324k 2.2µH COUT 330µF 1nF 324k 649k 10µF RSENSE 7mΩ MBOT BG VIN1 2.
PAGE 22
LTC3374 Applications Information 2.7V TO 5.5V 10µF 2.5V 4A 2.2µH 100µF 665k VIN1 VIN6 SW1 SW2 SW3 SW4 FB1 SW8 SW7 SW6 2.2µH 324k 10µF FB6 309k 10µF 68µF 1.2V 3A 649k VIN2 VIN7 FB2 FB7 10µF LTC3374 10µF 10µF VIN3 VIN8 FB3 FB8 VIN4 VIN5 SW5 10µF 2.2µH 511k FB4 EN1 EN5 EN6 SYNC MODE 10µF FB5 511k EN2 EN3 EN4 EN7 EN8 MICROPROCESSOR CONTROL 22µF 1.6V 1A VCC PGOOD_ALL TEMP 10µF MICROPROCESSOR CONTROL RT EXPOSED PAD 3374 F05 Figure 5.
PAGE 23
LTC3374 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 0.70 ± 0.05 5.50 ± 0.05 5.15 ± 0.05 4.10 ± 0.05 3.00 REF 3.15 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 5.5 REF 6.10 ± 0.05 7.50 ± 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.75 ± 0.05 5.00 ± 0.10 PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 3.
PAGE 24
LTC3374 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev C) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 4.50 REF 2.74 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .
PAGE 25
LTC3374 Revision History REV DATE DESCRIPTION A 11/13 Modified Figure 5 – removed a resistor. PAGE NUMBER 22 3374fa 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. For more information www.linear.
PAGE 26
LTC3374 Typical Application Combined Bucks with 3MHz Switch Frequency and Sequenced Power Up 2.25V TO 5.5V 10µF 10µF 10µF 2V 3A 1µH 68µF 649k VIN1 VIN8 FB8 VIN2 FB2 VIN7 VIN3 FB3 SW7 SW8 SW1 SW2 SW3 FB7 1.2V 1A VIN6 FB6 VIN4 10µF 1µH SW5 SW6 SW4 FB4 1.02M 2.5V 2A 475k VCC PGOOD_ALL MICROPROCESSOR CONTROL 47µF FB5 649k 10µF 3.3V 2A 2.5V TO 5.5V 10µF VIN5 324k 2.7V TO 5.5V 47µF LTC3374 1µH 22µF 1.02M 324k 432k 10µF 10µF 1µH FB1 2.25V TO 5.5V 3.3V TO 5.