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LTC3605A

3605afg

For more information www.linear.com/LTC3605A

LTC3605A

CLKOUT

CLKIN

PGOOD

RUN

INTV

BOOST

2.2µF

47µF

×2

3605A TA01a

OUT

3.3V

0.1µF

220pF

11.5k

2.55k

16k

162k

1µH

22µF

×2

4V TO 20V

ITH

PGND

Typical applicaTion

FeaTures

applicaTions

DescripTion

20V, 5A Synchronous

Step-Down Regulator

The LT C

3605A is a high efficiency, monolithic synchro-

nous buck regulator using a phase lockable controlled

on-time constant frequency

, current mode architecture.

PolyPhase operation allows multiple LTC3605A regula

tors to run out of phase while using minimal input and

output capacitance. The operating supply voltage range

is from 20V down to 4V, making it suitable for dual, triple

or quadruple lithium-ion battery inputs as well as point

of load power supply applications from a 12V or 5V rail.

The operating frequency is programmable from 800kHz to

4MHz with an external resistor. The high frequency capa

bility allows the use of small surface mount inductors. For

switching noise sensitive applications,

it can be externally

synchronized from 800kHz to 4MHz. The PHMODE pin

allows user control of the phase of the outgoing clock

signal. The unique constant frequency/controlled on-time

architecture is ideal for high step-down ratio applications

that are operating at high frequency while demanding

fast transient response. Two internal phase-lock loops

synchronize the internal oscillator to the external clock

and also servos the regulator on-time to lock on to either

the internal clock or the external clock if it’s present.

High Efficiency 1MHz, 5A Step-Down Regulator

High Efﬁciency: Up to 96%

5A Output Current

4V to 20V V

Range

Integrated Power N-Channel MOSFETs

(70mΩ Top and 35mΩ Bottom)

Adjustable Frequency 800kHz to 4MHz

PolyPhase

Operation (Up to 12 Phases)

Output Tracking

0.6V ±1% Reference Accuracy

Current Mode Operation for Excellent Line and Load

Transient Response

Shutdown Mode Draws Less Than 15µA Supply Current

LTC3605: 15V Absolute Maximum V

LTC3605A: 22V Absolute Maximum V

The LTC3605A Is Pin Compatible with the LTC3605

Available in 24-Pin (4mm × 4mm) QFN Package

Point of Load Power Supply

Portable Instruments

Distributed Power Systems

Battery-Powered Equipment

Efficiency and Power Loss

L, LT , LT C , LT M , PolyPhase, OPTI-LOOP, Linear Technology and the Linear logo are registered

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

respective owners. Protected by U.S. Patents, including 5481178, 5847554, 6580258, 6304066,

6476589, 6774611.

LOAD CURRENT (A)

0.01

EFFICIENCY (%)

POWER LOSS (W)

0.1 1 10

3605A TA01b

100

0.1

0.01

OUT

= 3.3V

= 8V

= 12V

= 20V

Downloaded from Arrow.com.

Summary of content (22 pages)

PAGE 1
LTC3605A 20V, 5A Synchronous Step-Down Regulator Features Description High Efficiency: Up to 96% nn 5A Output Current nn 4V to 20V V Range IN nn Integrated Power N-Channel MOSFETs (70mΩ Top and 35mΩ Bottom) nn Adjustable Frequency 800kHz to 4MHz nn PolyPhase® Operation (Up to 12 Phases) nn Output Tracking nn 0.
PAGE 2
LTC3605A Absolute Maximum Ratings Pin Configuration (Note 1) SVIN BOOST INTVCC SGND CLKOUT CLKIN TOP VIEW 24 23 22 21 20 19 RT 1 18 PVIN PHMODE 2 17 PVIN MODE 3 16 SW 25 PGND FB 4 15 SW 14 SW ITH 6 13 SW SW SW 9 10 11 12 PGND 8 VON 7 RUN TRACK/SS 5 PGOOD PVIN, SVIN, SW Voltage.............................. –0.3V to 22V SW Transient Voltage...................................–2V to 24.5V BOOST Voltage...........................–0.3V to PVIN + INTVCC RUN Voltage.....................
PAGE 3
LTC3605A Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ ≈ TA = 25°C (Note 2). VIN = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX ILIM Positive Inductor Valley Current Limit Negative Inductor Valley Current Limit RTOP Top Power NMOS On-Resistance 5 6 –5 7.5 A A 70 150 mΩ RBOTTOM Bottom Power NMOS On-Resistance INTVCC = 3.
PAGE 4
LTC3605A Typical Performance Characteristics TA = 25°C unless otherwise specified. 2.0 70 60 50 40 30 20 VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 10 0 0.01 0.1 1 LOAD CURRENT (A) 1.5 1.0 0.5 0 10 0 4 12 8 INPUT VOLTAGE (V) 3605A G01 10 5 4 0 MODE = 3.3V NO LOAD INTERNAL ITH COMPENSATION (ITH = 3.3V) 1.0 TOP FET 10 5 80 60 BOTTOM FET 40 0.5 1 1.5 2 2.5 3 3.5 FREQUENCY (MHz) 4 4.5 20 0.5 VIN = 12V VOUT = 1.2V f = 1MHz MODE = INTVCC 0 EXTERNAL ITH COMPENSATION –0.5 –1.
PAGE 5
LTC3605A Typical Performance Characteristics TA = 25°C unless otherwise specified. Switching Frequency vs RT 350 4.0 SWITCH LEAKAGE (nA) FREQUENCY (MHz) 3.5 3.0 2.5 2.0 1.5 1.0 Efficiency vs VIN 96 300 94 250 92 200 150 100 0 50 100 150 200 250 300 350 400 450 500 RT (kΩ) 0 0 2 4 6 8 10 12 VIN (V) 1.5 1.0 0.
PAGE 6
LTC3605A Pin Functions RT (Pin 1): Oscillator Frequency Programming Pin. Connect an external resistor (between 200k to 40k) from RT to SGND to program the frequency from 800kHz to 4MHz. Since the synchronization range is ±30% of set frequency, be sure that the set frequency is within this percentage range of the external clock to ensure frequency lock. VON (Pin 9): On-Time Voltage Input. Voltage trip point for the on-time comparator.
PAGE 7
LTC3605A Block Diagram VOUT VON 100K 0.6V 3pF 9 3 MODE 6V 35pF SVIN 3.3V REG ION PLL-SYNC (±30%) CIN2 CIN 17-18 ION INTVCC OST x= PVIN 1Ω 19 21 V tON = VON (0.64pF) IION VIN INTVCC R S BOOST Q 20 CB TG 12 x OSC RT 1 + PHMODE 2 RT CLKIN 24 ON 20k + IREV ICMP – OSC PLL-SYNC (±30%) – RUN CLKOUT 11–16 SENSE– BG CVCC 10, 25 FOLDBACK DISABLED AT START-UP 3.3µA + 0µA TO 10µA M2 PGND 3pF 35pF COUT DB SENSE+ –3.3µA TO 6.
PAGE 8
LTC3605A Operation Main Control Loop The LTC3605A is a current mode monolithic step-down regulator. In normal operation, the internal top power MOSFET is turned on for a fixed interval determined by a one-shot timer, OST. When the top power MOSFET turns off, the bottom power MOSFET turns on until the current comparator, ICMP , trips, restarting the one-shot timer and initiating the next cycle. Inductor current is determined by sensing the voltage drop across the bottom power MOSFET ’s VDS.
PAGE 9
LTC3605A Operation PVIN/SVIN Voltage Differential Programming Switching Frequency SVIN should be tied to PVIN with a low pass filter of 1Ω to 10Ω and 0.1μF.
PAGE 10
LTC3605A Operation Multiphase Operation For output loads that demand more than 5A of current, multiple LTC3605As can be cascaded to run out of phase to provide more output current. The CLKIN pin allows the LTC3605A to synchronize to an external clock (±30% of frequency programmed by RT) and the internal phaselocked-loop allows the LTC3605A to lock onto CLKIN’s phase as well.
PAGE 11
LTC3605A Operation derate the capacitor, or 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. For low input voltage applications, sufficient bulk input capacitance is needed to minimize transient effects during output load changes.
PAGE 12
LTC3605A Operation Lower ripple current reduces core losses in the inductor, ESR losses in the output capacitors and output voltage ripple. Highest efficiency operation is obtained at low frequency with small ripple current. However, achieving this requires a large inductor. There is a trade-off between component size, efficiency and operating frequency. A reasonable starting point is to choose a ripple current that is about 2.5A. This is especially important at low VOUT operation where VOUT is 1.
PAGE 13
LTC3605A Operation Table 1. Inductor Selection Table INDUCTANCE DCR MAX CURRENT DIMENSIONS HEIGHT 6.7mm × 7mm 3mm Vishay IHLP-2525CZ-01 Series 0.33µH 4.1mW 18A 0.47µH 6.5mW 13.5A 0.68µH 9.4mW 11A 0.82µH 11.8mW 10A 1.0µH 14.2mW 9A Vishay IHLP-1616BZ-11 Series 0.22µH 4.1mW 12A 0.47µH 15mW 7A 4.3mm × 4.7mm 2.0mm 7mm × 7.7mm 2.0mm 6.9mm × 7.7mm 3.0mm Toko FDV0620 Series 0.20µH 4.5mW 12.4A 0.47µH 8.3mW 9A 1µH 18.3mW 5.7A NEC/Tokin MLC0730L Series 0.47µH 4.5mW 16.
PAGE 14
LTC3605A Operation 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. Although all dissipative elements in the circuit produce losses, three main sources usually account for most of the losses in LTC3605A circuits: 1) I2R losses, 2) switching and biasing losses, 3) other losses. 1.
PAGE 15
LTC3605A Operation The VIN current during 1MHz force continuous operation with no load is about 11mA, which includes switching and internal biasing current loss, transition loss, inductor core loss and other losses in the application. Therefore, the total power dissipated by the part is: PD = IOUT2 • RSW + VIN • IVIN (No Load) = 25A2 • 40.25mΩ + 12V • 11mA = 1.14W The QFN 4mm × 4mm package junction-to-ambient thermal resistance, θJA, is around 37°C/W.
PAGE 16
LTC3605A Operation CIN L1 VIN GND VOUT VIN VOUT COUT GND 3605A F03b 3605A F03a Figure 3a. Sample PCB Layout—Topside Figure 3b. Sample PCB Layout—Bottom Side 4. Solder the Exposed Pad (Pin 25) on the bottom of the package to the PGND plane. Connect this PGND plane to other layers with thermal vias to help dissipate heat from the LTC3605A. Because efficiency is important at both high and low load current, discontinuous mode operation will be utilized.
PAGE 17
LTC3605A Typical Applications 12V to 1.2V 1MHz Buck Regulator C1 2.2µF 0.1µF D1 10Ω 23 24 1 162k 2 3 4 5 12k 330pF 6 10pF 0.1µF 22 21 20 CLKIN CLKOUT SGND INTVCC BOOST SVIN RT PVIN PHMODE PVIN MODE SW LTC3605A FB SW TRACK/SS SW ITH SW RUN PGOOD 7 SVIN VON PGND 9 10 8 SW 11 CIN 22µF ×2 19 18 VIN 4V TO 20V 0.1µF 17 16 L1 0.68µH 15 47pF 14 COUT 47µF ×2 13 SW 4.99k VOUT 1.2V 5A 4.
PAGE 18
LTC3605A Typical Applications 12V, 10A 2-Phase Single Output Regulator 0.1µF C1 2.2µF D1 10Ω 24 1 162k 2 3 4 5 6 5.4k 470pF 0.1µF 23 22 21 20 CLKIN CLKOUT SGND INTVCC BOOST SVIN RT PVIN PHMODE PVIN MODE 18 SW TRACK/SS SW 10pF PGOOD 7 VON PGND 9 10 8 SVIN SW 11 L1 1.5µH 15 14 10k COUT1 47µF ×2 13 SW RUN 0.1µF 16 SW FB VIN 4V TO 20V 17 LTC3605A ITH CIN1 22µF ×2 19 SW 100pF VOUT 3.3V 10A 2.21k 12 100k PGND SGND 0.1µF C2 2.
PAGE 19
LTC3605A Typical Applications Dual Output Tracking Application C1 2.2µF 0.1µF D1 10Ω 23 24 1 162k 2 3 4 5 16.2k 100pF 6 10pF 0.1µF 22 21 20 CLKIN CLKOUT SGND INTVCC BOOST SVIN RT PVIN PHMODE PVIN MODE 18 SW TRACK/SS SW ITH SW PGOOD 7 VON PGND 9 10 8 SVIN1 SW L1 0.33µH 15 14 7.5k COUT1 47µF 13 11 4.99k PGND SGND 0.1µF D2 1 162k 2 3 4 5 16.
PAGE 20
LTC3605A Package Description Please refer to http://www.linear.com/product/LTC3605A#packaging for the most recent package drawings. UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697 Rev B) 0.70 ±0.05 4.50 ±0.05 2.45 ±0.05 3.10 ±0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ±0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 ±0.05 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER 23 24 PIN 1 TOP MARK (NOTE 6) 0.
PAGE 21
LTC3605A Revision History REV DATE DESCRIPTION A 12/12 Updated VVIN_OV specification. PAGE NUMBER B 09/13 Clarified conditions for electrical specifications. Clarified specifications in the Electrical Characteristics section. Clarified TRACK/SS pin description. Clarified schematics. C 04/15 D 08/15 E 11/15 3 2, 3 3 6 7, 17 Clarified the Main Control Loop description and added RUN Threshold section header. 8 Clarified negative valley current limit parameter.
PAGE 22
LTC3605A Typical Application –3.6V Negative Converter C1 2.2µF CIN 22µF ×2 0.1µF D1 10Ω 24 1 2 162k 3 4 5 16.2k 470pF 6 47pF 0.1µF 23 22 21 20 CLKIN CLKOUT SGND INTVCC BOOST SVIN RT PVIN PHMODE PVIN MODE SW LTC3605A FB SW TRACK/SS SW ITH SW RUN 7 SVIN PGOOD VON PGND 9 10 8 SW 11 VIN 3V TO 16V 19 0.1µF 18 17 16 L1 1µH 15 14 24.9k 13 COUT 47µF ×2 SW 4.99k 12 100k 3605A TA05 –3.6V Negative Converter Efficiency VOUT –3.6V 2A –3.