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LTC3621/LTC3621-2

3621fb

For more information www.linear.com/LTC3621

Typical applicaTion

FeaTures DescripTion

17V, 1A Synchronous

Step-Down Regulator with

3.5µA Quiescent Current

The LT C

3621/LTC3621-2 is a high efficiency 17V, 1A

synchronous monolithic step-down regulator. The switch

ing frequency is fixed to 1MHz or 2.25MHz with a ±40%

synchronizing range. The regulator features ultralow quies

cent current and high efficiencies over a wide V

OUT

range.

The step-down regulator operates from an input voltage

range of 2.7V to 17V and provides an adjustable output

range from 0.6V to V

while delivering up to 1A of output

current. A user-selectable mode input is provided to allow

the user to trade off ripple noise for light load efficiency;

Burst Mode operation provides the highest efficiency at

light loads, while pulse-skipping mode provides the lowest

voltage ripple. The MODE pin can also be used to allow the

user to sync the switching frequency to an external clock.

LTC3621 Options

PART NAME FREQUENCY V

OUT

LTC3621 1.00MHz Adjustable

LTC3621-3.3 1.00MHz 3.3V

LTC3621-5 1.00MHz 5V

LTC3621-2 2.25MHz Adjustable

LTC3621-23.3 2.25MHz 3.3V

LTC3621-25 2.25MHz 5V

Efficiency and Power Loss vs Load at 1MHz

2.5V V

OUT

with 400mA Burst Clamp, f

= 1MHz

applicaTions

Wide V

Range: 2.7V to 17V

Wide V

OUT

Range: 0.6V to V

95% Max Efficiency

Low I

< 3.5µA, Zero-Current Shutdown

Constant Frequency (1MHz/2.25MHz)

Full Dropout Operation with Low I

1A Rated Output Current

±1% Output Voltage Accuracy

Current Mode Operation for Excellent Line and Load

Transient Response

Synchronizable to External Clock

Pulse-Skipping, Forced Continuous, Burst Mode

Operation

Internal Compensation and Soft-Start

Overtemperature Protection

Compact 6-Lead DFN (2mm × 3mm) Package or

Thermally-Enhanced MS8E Package with Power

Good Output and Independent SGND Pin

Portable-Handheld Scanners

Industrial and Embedded Computing

Automotive Applications

Emergency Radio

L, LT, LTC, LTM, Burst Mode, Linear Technology, the Linear logo and LTSpice are registered

trademarks and Hot Swap and LTpowerCAD are trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners. Protected by U.S. Patents,

including 5481178, 6580258, 6498466, 6611131, 6177787, 5705919, 5847554.

604k 22pF

1µF

22µF

3621 TA01a

4.7µH

OUT

2.5V

191k

RUN

2.7V TO 17V

LTC3621

GND

MODE/SYNC

INTV

10µF

LOAD CURRENT (A)

EFFICIENCY (%)

POWER LOSS (W)

100

0.2

0.4 0.6

3621 TA01b

0.1

0.6

0.4

0.5

0.3

0.2

0.8

EFFICIENCY

POWER LOSS

OUT

= 5V

OUT

= 3.3V

OUT

= 2.5V

= 12V

Summary of content (18 pages)

PAGE 1
LTC3621/LTC3621-2 17V, 1A Synchronous Step-Down Regulator with 3.5µA Quiescent Current Description Features n n n n n n n n n n n n n n Wide VIN Range: 2.7V to 17V Wide VOUT Range: 0.6V to VIN 95% Max Efficiency Low IQ < 3.5µA, Zero-Current Shutdown Constant Frequency (1MHz/2.
PAGE 2
LTC3621/LTC3621-2 Absolute Maximum Ratings (Note 1) VIN Voltage.................................................. 17V to –0.3V RUN Voltage................................................ VIN to –0.3V MODE/SYNC, FB Voltages............................. 6V to –0.3V INTVCC, PGOOD Voltages............................. 6V to –0.3V Operating Junction Temperature Range (Notes 3, 6, 7)......................................... –40°C to 125°C Storage Temperature Range...................
PAGE 3
LTC3621/LTC3621-2 Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3621EMS8E-2#PBF LTC3621EMS8E-2#TRPBF LTGHZ 8-Lead Plastic MSOP –40°C to 125°C LTC3621IMS8E-2#PBF LTC3621IMS8E-2#TRPBF LTGHZ 8-Lead Plastic MSOP –40°C to 125°C LTC3621EMS8E-23.3#PBF LTC3621EMS8E-23.3#TRPBF LTGNZ 8-Lead Plastic MSOP –40°C to 125°C LTC3621IMS8E-23.3#PBF LTC3621IMS8E-23.
PAGE 4
LTC3621/LTC3621-2 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TJ = 25°C. (Note 3) VIN = 12V, unless otherwise noted.
PAGE 5
LTC3621/LTC3621-2 Typical Performance Characteristics TJ = 25°C, unless otherwise noted. VIN Supply Current vs Input Voltage Efficiency vs Load Current (Burst Mode Operation) 100 Efficiency vs Load at Dropout Operation 100 5 90 90 70 60 50 40 30 20 VOUT = 2.5V VOUT = 3.3V 10 VIN = 12V VOUT = 5V FREQUENCY = 2.25MHz 0 0.001 0.1 0.
PAGE 6
LTC3621/LTC3621-2 Typical Performance Characteristics TJ = 25°C, unless otherwise noted. Oscillator Frequency vs Supply Voltage Efficiency vs Load at 1MHz 2.50 90 2.45 80 EFFICIENCY (%) 70 60 50 40 30 20 VOUT = 2.5V VOUT = 3.3V VOUT = 5V 10 VIN = 12V 0 0.0001 0.001 0.1 0.01 LOAD CURRENT (A) 600.5 600.0 2.40 REFERENCE VOLTAGE OSCILLATOR FREQUENCY (MHz) 100 Reference Voltage vs Temperature 2.35 2.30 2.25 2.20 2.15 2.10 599.5 599.0 598.5 598.0 2.05 1 2.
PAGE 7
LTC3621/LTC3621-2 Pin Functions (DFN/MSOP) SW (Pin 1/Pin 1): Switch Node Connection to the Inductor of the Step-Down Regulator. INTVCC (Pin 5/Pin 6): Low Dropout Regulator. Bypass with at least 1µF to Ground. VIN (Pin 2/Pin 2): Input Voltage of the Step-Down Regulator. MODE/SYNC (Pin 6/Pin 7): Burst Mode Select and External Clock Synchronization of the Step-Down Regulator.
PAGE 8
LTC3621/LTC3621-2 Operation The LTC3621 uses a constant-frequency, peak current mode architecture. It operates through a wide VIN range and regulates with ultralow quiescent current. The operation frequency is set at either 2.25MHz or 1MHz and can be synchronized to an external oscillator ±40% of the inherent frequency. To suit a variety of applications, the selectable MODE/SYNC pin allows the user to trade off output ripple for efficiency.
PAGE 9
LTC3621/LTC3621-2 Operation selected, the part will transition in and out of sleep mode depending on the output load current. This significantly reduces the quiescent current, thus prolonging the use of the input supply. VIN Overvoltage Protection In order to protect the internal power MOSFET devices against transient voltage spikes, the LTC3621 constantly monitors the VIN pin for an overvoltage condition. When VIN rises above 19V, the regulator suspends operation by shutting off both power MOSFETs.
PAGE 10
LTC3621/LTC3621-2 Applications Information the load transient response. The output ripple, ∆VOUT, is determined by: ∆VOUT < ∆IL 1   +ESR 8 • f •COUT  The output ripple is highest at maximum input voltage since ∆IL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic, and ceramic capacitors are all available in surface mount packages.
PAGE 11
LTC3621/LTC3621-2 Applications Information Inductor Selection Given the desired input and output voltages, the inductor value and operating frequency determine the ripple current: ∆IL = VOUT  V  1– OUT f •L  VIN(MAX)  Lower ripple current reduces power 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.
PAGE 12
LTC3621/LTC3621-2 Applications Information Table 1. Inductor Selection Table INDUCTOR IHLP-1616BZ-11 Series IHLP-2020BZ-01 Series FDV0620 Series MPLC0525L Series XFL4020 Series RLF7030 Series WE-TPC 4828 Series INDUCTANCE (µH) 1.0 2.2 4.7 1 2.2 3.3 4.7 5.6 6.8 1 2.2 3.3 4.7 1 1.5 2.2 1.0 1.5 2.2 3.3 4.7 1 1.5 2.2 3.3 4.7 6.8 1.2 1.8 2.2 2.7 3.3 3.9 4.7 DCR (mΩ) 24 61 95 18.9 45.6 79.2 108 113 139 18 37 51 68 16 24 40 10.8 14.4 21.3 34.8 52.2 8.8 9.6 12 20 31 45 17 20 23 27 30 47 52 MAX CURRENT (A) 4.
PAGE 13
LTC3621/LTC3621-2 Applications Information 2. The switching current is the sum of the MOSFET driver and control currents. The power MOSFET driver current results from switching the gate capacitance of the power MOSFETs. Each time a power MOSFET gate is switched from low to high to low again, a packet of charge dQ moves from VIN to ground. The resulting dQ/dt is a current out of VIN that is typically much larger than the DC control bias current.
PAGE 14
LTC3621/LTC3621-2 Applications Information Board Layout Considerations When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3621 (refer to Figure 3). Check the following in your layout: 5. Keep sensitive components away from the SW pin. The feedback resistors and INTVCC bypass capacitors should be routed away from the SW trace and the inductor. 6. A ground plane is preferred. 7.
PAGE 15
LTC3621/LTC3621-2 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 (2 SIDES) 2.15 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 1.35 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP R = 0.05 TYP 2.00 ±0.10 (2 SIDES) 3.00 ±0.10 (2 SIDES) 0.40 ±0.10 4 6 1.65 ±0.10 (2 SIDES) PIN 1 NOTCH R0.
PAGE 16
LTC3621/LTC3621-2 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev K) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 (.074) 1 1.88 ±0.102 (.074 ±.004) 0.29 REF 1.68 (.066) 0.889 ±0.127 (.035 ±.005) 0.05 REF 5.10 (.201) MIN DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 1.68 ±0.102 3.
PAGE 17
LTC3621/LTC3621-2 Revision History REV DATE DESCRIPTION A 08/13 Updated Efficiency curve 1 Input quiescent current limits changed 2 Oscillator frequency (fOSC) conditions changed 2 Clarified Features and Description 1 Clarified options 1 Clarified ordering info and Absolute Maximum Ratings 2 B 03/14 PAGE NUMBER 2-3 Added Note 7 Clarified electrical specifications 3 Clarified pin descriptions, Block Diagram 6 Clarified Operation description 7 Added box to figure 7 Clarified Appli
PAGE 18
LTC3621/LTC3621-2 Typical Application 5VOUT with 400mA Burst Mode Operation, 2.25MHz L1 3.3µH VIN 12V CIN 10µF SW VIN R3 187k LTC3621-2 RUN FB MODE/SYNC INTVCC GND CFB 22pF VOUT COUT 5V 22µF 3621 TA02 R4 25.5k C1 1µF 3621 TA02 1.2VOUT, Forced Continuous Mode, 1MHz VIN L1 3.3µH 2.7V TO 17V CIN 10µF 1.2V SW VIN R1 604k LTC3621 RUN FB MODE/SYNC INTVCC GND COUT 22µF CFB 22pF VOUT R5 604k C1 1µF V 1V 3621 TA03 1.2VOUT, Synchronized to 600kHz, Forced Continuous Mode VIN 2.