Datasheet

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LTC3411

sn3411 3411fs

The LTC

3411 is a constant frequency, synchronous,

step- down DC/DC converter. Intended for medium power

applications, it operates from a 2.63V to 5.5V input voltage

range and has a user configurable operating frequency up

to 4MHz, allowing the use of tiny, low cost capacitors and

inductors 2mm or less in height. The output voltage is

adjustable from 0.8V to 5V. Internal sychronous 0.11Ω

power switches with 1.6A peak current ratings provide

high efficiency. The LTC3411’s current mode architecture

and external compensation allow the transient response

to be optimized over a wide range of loads and output

capacitors.

The LTC3411 can be configured for automatic power

saving Burst Mode operation to reduce gate charge losses

when the load current drops below the level required for

continuous operation. For reduced noise and RF interfer-

ence, the SYNC/MODE pin can be configured to skip

pulses or provide forced continuous operation.

To further maximize battery life, the P-channel MOSFET is

turned on continuously in dropout (100% duty cycle) with

a low quiescent current of 60µA. In shutdown, the device

draws <1µA.

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Notebook Computers

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Digital Cameras

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Cellular Phones

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Handheld Instruments

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Board Mounted Power Supplies

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

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Small 10-Lead MSOP or DFN Package

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Uses Tiny Capacitors and Inductor

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High Frequency Operation: Up to 4MHz

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High Switch Current: 1.6A

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Low R

DS(ON)

Internal Switches: 0.110Ω

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High Efficiency: Up to 95%

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Stable with Ceramic Capacitors

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Current Mode Operation for Excellent Line

and Load Transient Response

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Short-Circuit Protected

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Low Dropout Operation: 100% Duty Cycle

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Low Shutdown Current: I

≤ 1µA

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Low Quiescent Current: 60µA

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Output Voltages from 0.8V to 5V

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Selectable Burst Mode

Operation

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Sychronizable to External Clock

1.25A, 4MHz, Synchronous

Step-Down DC/DC Converter

Efficiency vs Load Current

Figure 1. Step-Down 2.5V/1.25A Regulator

Burst Mode is a registered trademark of Linear Technology Corporation.

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

SYNC/MODEV

LTC3411

PGOOD

SHDN/R

PGNDSGND

2.2µH

OUT

2.5V/1.25A

2.63V TO 5.5V

887k

412k

1000pF

3411 F01

22µF

13k

22µF

324k

NOTE: IN DROPOUT, THE OUTPUT TRACKS

THE INPUT VOLTAGE

C1, C2: TAIYO YUDEN JMK325BJ226MM

L1: TOKO A914BYW-2R2M (D52LC SERIES)

LOAD CURRENT (mA)

EFFICIENCY (%)

100

1 100 1000

3411 TA01

= 3.3V

OUT

= 2.5V

= 1MHz

Burst Mode OPERATION

Summary of content (20 pages)

PAGE 1
LTC3411 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®3411 is a constant frequency, synchronous, step- down DC/DC converter. Intended for medium power applications, it operates from a 2.63V to 5.5V input voltage range and has a user configurable operating frequency up to 4MHz, allowing the use of tiny, low cost capacitors and inductors 2mm or less in height. The output voltage is adjustable from 0.8V to 5V. Internal sychronous 0.
PAGE 2
LTC3411 W W U W ABSOLUTE AXI U RATI GS (Note 1) PVIN, SVIN Voltages .....................................– 0.3V to 6V VFB, ITH, SHDN/RT Voltages .......... – 0.3V to (VIN + 0.3V) SYNC/MODE Voltage .................... – 0.3V to (VIN + 0.3V) SW Voltage ................................... – 0.3V to (VIN + 0.3V) PGOOD Voltage ...........................................– 0.3V to 6V Operating Ambient Temperature Range (Note 2) ..................................................
PAGE 3
LTC3411 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V, RT = 324k unless otherwise specified. (Note 2) SYMBOL PGOOD PARAMETER Power Good Threshold RPGOOD Power Good Pull-Down On-Resistance CONDITIONS VFB Ramping Up, SHDN/RT = 1V VFB Ramping Down, SHDN/RT = 1V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
PAGE 4
LTC3411 U U U PI FU CTIO S PIN 1 2 3 4 5 6 7 8 9 10 NAME SHDN/RT SYNC/MODE SGND SW PGND PVIN SVIN PGOOD VFB ITH NOMINAL (V) TYP MAX 0.8 SVIN SVIN 0 0 PVIN 0 – 0.3 5.5 2.5 5.5 0 SVIN 0 0.8 1.0 0 1.5 DESCRIPTION Shutdown/Timing Resistor Mode Select/Sychronization Pin Signal Ground Switch Node Main Power Ground Main Power Supply Signal Power Supply Power Good Pin Output Feedback Pin Error Amplifier Compensation and Run Pin MIN – 0.3 0 ABSOLUTE MAX (V) MIN MAX – 0.3 SVIN + 0.3 – 0.3 SVIN + 0.3 – 0.
PAGE 5
LTC3411 U W TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation Line Regulation 0.4 0.50 Burst Mode OPERATION 0.2 VIN = 3.3V VOUT = 2.5V VOUT ERROR (%) 0 FORCED CONTINUOUS –0.1 –0.2 0.35 0.30 0.25 0.20 IOUT = 1.25A 0.15 IOUT = 400mA 4 2 0 –2 –4 0.10 –0.4 0.05 –8 –0.5 0 –10 10 100 1000 LOAD CURRENT (mA) 10000 2 3 4 VIN (V) 5 3411 G07 –6 6 2 100 10 6 –4 6 120 TA = 25°C 115 95 RDS(ON) (mΩ) EFFICIENCY (%) 4 0 5 RDS(ON) vs VIN VIN = 3.3V VOUT = 2.
PAGE 6
LTC3411 W BLOCK DIAGRA SVIN SGND ITH PVIN 7 3 10 6 0.8V PMOS CURRENT COMPARATOR ITH LIMIT VOLTAGE REFERENCE + BCLAMP + – – VFB 9 ERROR AMPLIFIER VB 0.74V + – B – + BURST COMPARATOR HYSTERESIS = 80mV SLOPE COMPENSATION OSCILLATOR 4 SW + 0.
PAGE 7
LTC3411 U OPERATIO The LTC3411 uses a constant frequency, current mode architecture. The operating frequency is determined by the value of the RT resistor or can be synchronized to an external oscillator. To suit a variety of applications, the selectable Mode pin, allows the user to trade-off noise for efficiency. The output voltage is set by an external divider returned to the VFB pin. An error amplfier compares the divided output voltage with a reference voltage of 0.
PAGE 8
LTC3411 U U W U APPLICATIO S I FOR ATIO A general LTC3411 application circuit is shown in Figure␣ 5. External component selection is driven by the load requirement, and begins with the selection of the inductor L1. Once L1 is chosen, CIN and COUT can be selected. A reasonable starting point for setting ripple current is ∆IL␣ =␣ 0.3 • ILIM, where ILIM is the peak switch current limit. The largest ripple current ∆IL occurs at the maximum input voltage.
PAGE 9
LTC3411 U U W U APPLICATIO S I FOR ATIO typical surface mount inductors that work well in LTC3411 applications. Table 1. Representative Surface Mount Inductors MANUFACTURER PART NUMBER MAX DC VALUE CURRENT DCR HEIGHT Toko A914BYW-2R2M-D52LC 2.2µH 2.05A 49mΩ 2mm Toko A915AY-2ROM-D53LC 2µH 3.3A 22mΩ 3mm Coilcraft D01608C-222 2.2µH 2.3A 70mΩ 3mm Coilcraft LP01704-222M 2.2µH 2.4A 120mΩ 1mm Sumida CDRH4D282R2 2.2µH 2.04A 23mΩ Sumida CDC5D232R2 2.2µH 2.16A 30mΩ 2.
PAGE 10
LTC3411 U W U U APPLICATIO S I FOR ATIO Once the ESR requirements for COUT have been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement, except for an all ceramic solution. In surface mount applications, multiple capacitors may have to be paralleled to meet the capacitance, ESR or RMS current handling requirement of the application. Aluminum electrolytic, special polymer, ceramic and dry tantulum capacitors are all available in surface mount packages.
PAGE 11
LTC3411 U U W U APPLICATIO S I FOR ATIO Setting the Output Voltage The LTC3411 develops a 0.8V reference voltage between the feedback pin, VFB, and the signal ground as shown in Figure 5. The output voltage is set by a resistive divider according to the following formula:  R2 VOUT ≈ 0.8V  1 +   R1 Keeping the current small (<5µA) in these resistors maximizes efficiency, but making them too small may allow stray capacitance to cause noise problems and reduce the phase margin of the error amp loop.
PAGE 12
LTC3411 U U W U APPLICATIO S I FOR ATIO The LTC3411 can also be synchronized to an external clock signal by the SYNC/MODE pin. The internal oscillator frequency should be set to 20% lower than the external clock frequency to ensure adequate slope compensation, since slope compensation is derived from the internal oscillator. During synchronization, the mode is set to pulse skipping and the top switch turn on is synchronized to the rising edge of the external clock.
PAGE 13
LTC3411 U W U U APPLICATIO S I FOR ATIO The output voltage settling behavior is related to the stability of the closed-loop system and will demonstrate the actual overall supply performance. For a detailed explanation of optimizing the compensation components, including a review of control loop theory, refer to Linear Technology Application Note 76.
PAGE 14
LTC3411 U W U U APPLICATIO S I FOR ATIO Thermal Considerations In a majority of applications, the LTC3411 does not dissipate much heat due to its high efficiency. However, in applications where the LTC3411 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part.
PAGE 15
LTC3411 U U W U APPLICATIO S I FOR ATIO current in these resistors should be kept small. Choosing 2µA with the 0.8V feedback voltage makes R1~400k. A close standard 1% resistor is 412k and R2 is then 887k. The compensation should be optimized for these components by examining the load step response but a good place to start for the LTC3411 is with a 13kΩ and 1000pF filter. The output capacitor may need to be increased depending on the actual undershoot during a load step.
PAGE 16
LTC3411 U TYPICAL APPLICATIO S VIN 2.63V TO 5.5V C1 22µF PGND PVIN SVIN RS1 1M BM PGOOD ITH VOUT 1.8V/2.5V/3.3V AT 1.25A R2 887K SYNC/MODE PS RS2 1M L1 2.2µH SW LTC3411 FC R5 100k PGOOD VFB SHDN/RT 3.3V SGND 2.5V 1.8V PGND R3 13k R4 324k C3 1000pF C2 22µF C4 22pF R1A 280k R1B 412k R1C 698k 3411 F07a SGND SGND GND SGND PGND NOTE: IN DROPOUT, THE OUTPUT TRACKS THE INPUT VOLTAGE C1, C2: TAIYO YUDEN JMK325BJ226MM L1: TOKO A914BYW-2R2M (D52LC SERIES) Figure 7.
PAGE 17
LTC3411 U TYPICAL APPLICATIO S Single Inductor, Positive, Buck-Boost Converter C1 22µF VIN 2.63V TO 5V 100k C7 10pF SVIN SW L1 3.3µH D1 SGND VFB SYNC/MODE ITH SHDN/RT R3 13k C2 22µF ×2 M1 VIN PGOOD + C4 47µF VOUT 3.
PAGE 18
LTC3411 U TYPICAL APPLICATIO S All Ceramic 2-Cell to 3.3V and 1.8V Converters VIN = 2V TO 3V L1 4.7µH D1 VOUT 3.3V 120mA/1A C5 22µF LTC3402 VIN +2 CELLS SHDN 1M VOUT SYNC/MODE PGOOD 604k VC C2 44µF (2 × 22µF) 1000pF RT 49.
PAGE 19
LTC3411 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 5) (DD10) DFN 0403 5 0.25 ± 0.05 1 0.75 ±0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 20
LTC3411 U TYPICAL APPLICATIO 2mm Height, 2MHz, Li-Ion to 1.8V Converter VIN 2.63V TO 4.2V C6 1µF + R5 100k C1 33µF PVIN PGOOD SVIN SW LTC3411 PGOOD L1 1µH + C4 22pF SYNC/MODE ITH C7 47pF R3 15k C3 470pF C2 33µF C5 1µF VOUT 1.8V AT 1.25A VFB SGND PGND SHDN/RT R4 154k R1 698k R2 887k 3411 TA04 C1, C2: AVX TPSB336K006R0600 C4, C5: TAIYO YUDEN LMK212BJ105MG L1: COILCRAFT DO1606T-102 Efficiency vs Load Current 100 95 2.5V 90 EFFICIENCY (%) 85 3.6V 80 75 70 4.2V 65 60 VOUT = 1.