Datasheet

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LTC3414

3414fb

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Point-of-Load Regulation

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Notebook Computers

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Portable Instruments

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Distributed Power Systems

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High Efficiency: Up to 95%

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4A Output Current

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Low Quiescent Current: 64μA

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Low R

DS(ON)

Internal Switch: 67mΩ

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Programmable Frequency: 300KHz to 4MHz

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2.25V to 5.5V Input Voltage Range

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±2% Output Voltage Accuracy

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0.8V Reference Allows Low Output Voltage

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Selectable Forced Continuous/Burst Mode

Operation

with Adjustable Burst Clamp

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Synchronizable Switching Frequency

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Low Dropout Operation: 100% Duty Cycle

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Power Good Output Voltage Monitor

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Overtemperature Protected

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Available in 20-Lead Exposed TSSOP Package

4A, 4MHz, Monolithic

Synchronous Step-Down Regulator

The LTC

3414 is a high efficiency monolithic synchro-

nous, step-down DC/DC converter utilizing a constant

frequency, current mode architecture. It operates from an

input voltage range of 2.25V to 5.5V and provides a

regulated output voltage from 0.8V to 5V while delivering

up to 4A of output current. The internal synchronous

power switch with 67mΩ on-resistance increases effi-

ciency and eliminates the need for an external Schottky

diode. Switching frequency is set by an external resistor or

can be synchronized to an external clock. 100% duty cycle

provides low dropout operation extending battery life in

portable systems. OPTI-LOOP

compensation allows the

transient response to be optimized over a wide range of

loads and output capacitors.

The LTC3414 can be configured for either Burst Mode

operation or forced continuous operation. Forced continu-

ous operation reduces noise and RF interference while

Burst Mode operation provides high efficiency by reduc-

ing gate charge losses at light loads. In Burst Mode

operation, external control of the burst clamp level allows

the output voltage ripple to be adjusted according to the

requirements of the application.

3414 F01a

SYNC/MODE V

PGOOD

PGND

SGND

RUN/SS

LTC3414

294k

22μF

OUT

0.47μH

OUT

2.5V AT 4A

2.7V TO 5.5V

1000pF

2.2M

470pF

ITH

75k

110k 392k

*Burst Mode OPERATION: C

OUT

= 470μF SANYO POSCAP 4TPB470M, R

ITH

= 20k

FORCED CONTINUOUS: C

OUT

= (2) 100μF TDKC4532X5ROJ107M, R

ITH

= 12.1k

LTC3414 Efficiency Curve

Figure 1. 2.5V/4A Step-Down Regulator

LOAD CURRENT (A)

EFFICIENCY (%)

100

0.001 0.1 1.0 10

3414 F01b

0.01

Burst Mode OPERATION

FORCED

CONTINUOUS

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

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

Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Protected by U.S. Patents, Including 5481178, 6580258, 6304066, 6127815, 6498466,

6611131, 6724174

Summary of content (16 pages)

PAGE 1
LTC3414 4A, 4MHz, Monolithic Synchronous Step-Down Regulator DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 95% 4A Output Current Low Quiescent Current: 64μA Low RDS(ON) Internal Switch: 67mΩ Programmable Frequency: 300KHz to 4MHz 2.25V to 5.5V Input Voltage Range ±2% Output Voltage Accuracy 0.
PAGE 2
LTC3414 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage ................................... –0.3V to 6V ITH, RUN/SS, VFB, SYNC/MODE Voltages .................................. –0.3 to VIN SW Voltages ................................. –0.3V to (VIN + 0.3V) Peak SW Sink and Source Current ......................... 9.5A Operating Temperature Range (Note 2) E, I Grades .............................................. – 40°C to 85°C MP Grade .....................
PAGE 3
LTC3414 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch On-Resistance vs Temperature, VIN = 3.3V Switch On-Resistance vs Input Voltage VREF vs Temperature, VIN = 3.3V 120 90 0.800 TA = 25°C 80 0.797 ON-RESISTANCE (mΩ) 0.798 100 PFET 70 ON-RESISTANCE (mΩ) VREF (V) 0.799 60 NFET 50 40 30 80 PFET NFET 60 40 20 0.796 20 10 0.795 –40 –20 0 0 2.25 2.75 3.25 3.75 4.25 4.75 5.
PAGE 4
LTC3414 U W TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Load Current, Forced Continuous 100 TA = 25°C 95 90 VIN = 3.3V 90 80 75 70 100 90 VIN = 3.3V 70 VIN = 5V 60 50 40 85 75 70 65 60 20 60 55 10 55 0 0.001 10 0.01 0.1 1 LOAD CURRENT (A) 3414 G10 Efficiency vs Input Voltage IOUT = 1A 94 VIN = 3.3V VOUT = 2.5V 50 0.001 10 0.01 0.1 1 LOAD CURRENT (A) 3414 G11 100 VOUT = 2.5V TA = 25°C Load Regulation 0 VIN = 3.3V VOUT = 2.
PAGE 5
LTC3414 U W TYPICAL PERFOR A CE CHARACTERISTICS Load Step Transient Burst Mode Operation OUTPUT VOLTAGE 100mV/DIV Start-Up Transient VRUN OUTPUT VOLTAGE INDUCTOR CURRENT 2A/DIV INDUCTOR CURRENT 2A/DIV 20μs/DIV 3414 G18 VIN = 3.3V, VOUT = 2.5V LOAD STEP = 250mA TO 4A 1ms/DIV VIN = 3.3V, VOUT = 2.5V LOAD = 4A 3414 G19 U U U PI FU CTIO S PGND (Pins 1, 10, 11, 20): Power Ground. Connect this pin closely to the (–) terminal of CIN and COUT. RT (Pin 2): Oscillator Resistor Input.
PAGE 6
LTC3414 W BLOCK DIAGRA 0.8V SVIN SGND ITH EXPOSED PAD PVIN PVIN 16 5 18 21 7 14 PMOS CURRENT COMPARATOR SLOPE COMPENSATION RECOVERY VOLTAGE REFERENCE + BCLAMP + – VFB 19 – 0.74V + ERROR AMPLIFIER SYNC/MODE – + V SLOPE COMPENSATION BURST COMPARATOR + OSCILLATOR – 4 LOGIC RUN SW 9 SW 12 SW – RUN/SS NMOS CURRENT COMPARATOR 8 13 SW + + 0.
PAGE 7
LTC3414 U OPERATIO ing harmonics out of a signal band. The output voltage ripple is minimized in this mode. During synchronization, the burst clamp is set to 0V, and each switching cycle begins at the falling edge of the clock signal. Burst Mode Operation Connecting the SYNC/MODE pin to a voltage in the range of 0V to 1V enables Burst Mode operation. In Burst Mode operation, the internal power MOSFETs operate intermittently at light loads. This increases efficiency by minimizing switching losses.
PAGE 8
LTC3414 U W U U APPLICATIO S I FOR ATIO The basic LTC3414 application circuit is shown in Figure 1. External component selection is determined by the maximum load current and begins with the selection of the operating frequency and inductor value followed by CIN and COUT. Operating Frequency Selection of the operating frequency is a tradeoff between efficiency and component size. High frequency operation allows the use of smaller inductor and capacitor values.
PAGE 9
LTC3414 U W U U APPLICATIO S I FOR ATIO CIN and COUT Selection The input capacitance, CIN, is needed to filter the trapezoidal wave current at the source of the top MOSFET. To prevent large voltage transients from occurring, a low ESR input capacitor sized for the maximum RMS current should be used. The maximum RMS current is given by: IRMS V = IOUT (MAX) OUT VIN VIN –1 VOUT This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2.
PAGE 10
LTC3414 U W U U APPLICATIO S I FOR ATIO Burst Clamp Programming Frequency Synchronization If the voltage on the SYNC/MODE pin is less than VIN by 1V, Burst Mode operation is enabled. During Burst Mode Operation, the voltage on the SYNC/MODE pin determines the burst clamp level, which sets the minimum peak inductor current, IBURST, for each switching cycle according to the following equation: The LTC3414’s internal oscillator can be synchronized to an external clock signal.
PAGE 11
LTC3414 U W U U APPLICATIO S I FOR ATIO The VIN quiescent current loss dominates the efficiency loss at very low load currents whereas the I2R loss dominates the efficiency loss at medium to high load currents. In a typical efficiency plot, the efficiency curve at very low load currents can be misleading since the actual power lost is of no consequence. 1.
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LTC3414 U W U U APPLICATIO S I FOR ATIO Design Example As a design example, consider using the LTC3414 in an application with the following specifications: VIN = 2.7V to 4.2V, VOUT = 2.5V, IOUT(MAX) = 4A, IOUT(MIN) = 100mA, f = 1MHz. Because efficiency is important at both high and low load current, Burst Mode operation will be utilized. First, calculate the timing resistor: ROSC = 3.08 • 1011 – 10k = 298k 1• 106 Use a standard value of 294k.
PAGE 13
LTC3414 U W U U APPLICATIO S I FOR ATIO Bottom Top Figure 3. LTC3414 Layout Diagram 1 ROSC 294k 2 3 RSS 2.2M CSS 1000pF X7R 4 5 6 7 8 + CIN2*** 330μF 9 10 PGND PGND VFB RT ITH SYNC/MODE RUN/SS PGOOD SVIN SGND C1 10pF X7R 20 19 18 R3 124k CITH 470pF X7R R2 78.7k RITH 20k R1 432k 17 16 PGOOD RPG 100k LTC3414 NC PVIN NC PVIN SW SW SW SW PGND PGND VIN 2.7V TO 5V CIN1 22μF X5R 2X 15 14 13 12 11 L1* 0.47μH COUT2 22μF X5R VOUT 2.
PAGE 14
LTC3414 U TYPICAL APPLICATIO S 3.3V, 4A Step-Down Regulator at 1MHz, Forced Continuous Mode 1 ROSC 294k 2 3 RSS 2.2M 4 CSS 1000pF X7R 5 6 7 8 + CIN2*** 150μF 9 10 PGND PGND VFB RT ITH SYNC/MODE PGOOD RUN/SS SVIN SGND 20 19 18 CC 100pF X7R CITH 470pF X7R RITH 12.1k R1 634k 17 NC PVIN PVIN SW SW SW SW PGND PGND C1 22pF X7R PGOOD RPG 100k 16 CIN1 22μF X5R 2x LTC3414 NC R2 200k 15 VIN 5V 14 L1* 0.68μH 13 VOUT 3.
PAGE 15
LTC3414 U PACKAGE DESCRIPTIO FE Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation CA 6.40 – 6.60* (.252 – .260) 4.95 (.195) 4.95 (.195) 20 1918 17 16 15 14 13 12 11 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 6.40 2.74 (.252) (.108) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 9 10 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.25 REF 0.50 – 0.75 (.020 – .030) NOTE: 1.
PAGE 16
LTC3414 U TYPICAL APPLICATIO 1.5V, 4A Step-Down Regulator at 1MHz, Burst Mode 1 ROSC 294k 2 3 RSS 2.2M 4 CSS 1000pF, X7R 5 6 7 8 + CIN2** 470μF 9 10 PGND PGND RT VFB SYNC/MODE RUN/SS ITH PGOOD SGND SVIN LTC3414 NC PVIN NC PVIN SW SW SW SW PGND PGND CC 100pF X7R 20 CITH 470pF X7R 19 18 R2 200k RITH 15k C1 39pF X7R R1 178k 17 16 PGOOD RPG 100k 15 14 13 12 11 * PULSE P1166.68IT ** SANYO POSCAP 4TPD470M L1* 0.44μH VIN 2.5V CIN1 22μF X5R 2x COUT2 22μF X5R VOUT 1.