Datasheet

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LT3436

3436fa

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

3A, 800kHz Step-Up

Switching Regulator

■

Constant 800kHz Switching Frequency

■

Wide Operating Voltage Range: 3V to 25V

■

High Efficiency 0.1Ω/3A Switch

■

1.2V Feedback Reference Voltage

■

±2% Overall Output Voltage Tolerance

■

Uses Low Profile Surface Mount External

Components

■

Low Shutdown Current: 11µA

■

Synchronizable from 1MHz to 1.4MHz

■

Current-Mode Control

■

Constant Maximum Switch Current Rating

at All Duty Cycles*

■

Available in a Small Thermally Enhanced

TSSOP-16 Package

The LT

3436 is an 800kHz monolithic boost switching

regulator. A high efficiency 3A, 0.1Ω switch is included on

the die together with all the control circuitry required to

complete a high frequency, current-mode switching regu-

lator. Current-mode control provides fast transient re-

sponse and excellent loop stability.

New design techniques achieve high efficiency at high

switching frequencies over a wide operating range. A low

dropout internal regulator maintains consistent perfor-

mance over a wide range of inputs from 24V systems to Li-

Ion batteries. An operating supply current of 1mA main-

tains high efficiency, especially at lower output currents.

Shutdown reduces quiescent current to 11µA. Maximum

switch current remains constant at all duty cycles. Syn-

chronization capability allows an external logic level signal

to increase the internal oscillator from 1MHz to 1.4MHz.

Full cycle-by-cycle switch current limit protection and ther-

mal shutdown are provided. High frequency operation al-

lows the reduction of input and output filtering components

and permits the use of tiny chip inductors. The LT3436 is

available in an exposed pad, 16-pin TSSOP package.

■

DSL Modems

■

Portable Computers

■

Battery-Powered Systems

■

Distributed Power

Efficiency vs Load Current

5V to 12V Boost Converter

LT3436

OUTPUT

12V

0.9A

†

INPUT

3436 TA01

10nF

470pF

4.7k

10k

90.9k

B220A

22µF

CERAMIC

4.7µF

CERAMIC

FBSHDN

OPEN

HIGH

= ON

GND

SYNC

†

MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.

3.9µH

LOAD CURRENT (A)

EFFICIENCY (%)

3436 TA01b

0.2

0.4

0.5

0.1 0.3

0.6

0.7

0.8

= 5V

OUT

= 12V

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

All other trademarks are the property of their respective owners.

*Protectd by U.S. Patents including 6535042, 6611131, 6498466

Summary of content (16 pages)

PAGE 1
LT3436 3A, 800kHz Step-Up Switching Regulator U FEATURES DESCRIPTIO ■ The LT®3436 is an 800kHz monolithic boost switching regulator. A high efficiency 3A, 0.1Ω switch is included on the die together with all the control circuitry required to complete a high frequency, current-mode switching regulator. Current-mode control provides fast transient response and excellent loop stability. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Constant 800kHz Switching Frequency Wide Operating Voltage Range: 3V to 25V High Efficiency 0.
PAGE 2
LT3436 W U U U W W W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) ORDER PART NUMBER TOP VIEW Input Voltage .......................................................... 25V Switch Voltage ......................................................... 35V SHDN Pin ............................................................... 25V FB Pin Current ....................................................... 1mA SYNC Pin Current ..................................................
PAGE 3
LT3436 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3436E is guaranteed to meet performance specifications from 0°C to 125°C. Specifications over the – 40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Minimum input voltage is defined as the voltage where the internal regulator enters lockout.
PAGE 4
LT3436 U W TYPICAL PERFOR A CE CHARACTERISTICS SHDN Supply Current TA = 25°C VIN = 15V 4.0 TA = 25°C 3.5 VIN CURRENT (µA) 1000 200 150 100 800 MINIMUM INPUT VOLTAGE 600 400 50 200 0 0 40 TA = 25°C SWITCH CURRENT 3.0 30 2.5 2.0 20 1.5 1.0 10 FB INPUT CURRENT (µA) VIN CURRENT (µA) 250 Current Limit Foldback Input Supply Current 1200 SWITCH PEAK CURRENT (A) 300 0.5 0 0.2 0.4 0.6 0.8 1.0 SHDN VOLTAGE (V) 1.2 1.
PAGE 5
LT3436 W BLOCK DIAGRAM The LT3436 is a constant frequency, current-mode boost converter. This means that there is an internal clock and two feedback loops that control the duty cycle of the power switch. In addition to the normal error amplifier, there is a current sense amplifier that monitors switch current on a cycle-by-cycle basis. A switch cycle starts with an oscillator pulse which sets the RS flip-flop to turn the switch on.
PAGE 6
LT3436 U U W U APPLICATIONS INFORMATION FB RESISTOR NETWORK The suggested resistance (R2) from FB to ground is 10k 1%. This reduces the contribution of FB input bias current to output voltage to less than 0.2%. The formula for the resistor (R1) from VOUT to FB is: R1 = R2(VOUT − 1. 2) 1.2 − R2(0.2µA) VSW LT3436 OUTPUT ERROR AMPLIFIER + 1.2V FB + AVX TPS, Sprague 593D 0.1 to 0.3 0.7 to 1.1 0.1 to 0.3 0.7 to 1.1 0.2 (typ) 0.5 (typ) C Case Size 3436 F02 GND Figure 2.
PAGE 7
LT3436 U W U U APPLICATIONS INFORMATION INDUCTOR CHOICE AND MAXIMUM OUTPUT CURRENT When choosing an inductor, there are 2 conditions that limit the minimum inductance; required output current, and avoidance of subharmonic oscillation. The maximum output current for the LT3436 in a standard boost converter configuration with an infinitely large inductor is: IOUT (MAX) = 3A VIN • η VOUT Where η = converter efficiency (typically 0.87 at high current).
PAGE 8
LT3436 U U W U APPLICATIONS INFORMATION CATCH DIODE The suggested catch diode (D1) is a B220A Schottky. It is rated at 2A average forward current and 20V reverse voltage. Typical forward voltage is 0.5V at 2A. The diode conducts current only during switch off time. Peak reverse voltage is equal to regulator output voltage. Average forward current in normal operation is equal to output current. SHUTDOWN AND UNDERVOLTAGE LOCKOUT LT3436 7µA 1.35V 3µA VCC SHDN C1 VH − VL 7µA 1.35V (VH − 1.
PAGE 9
LT3436 U W U U APPLICATIONS INFORMATION SYNCHRONIZATION The SYNC pin, is used to synchronize the internal oscillator to an external signal. The SYNC input must pass from a logic level low, through the maximum synchronization threshold with a duty cycle between 20% and 80%. The input can be driven directly from a logic level output. The synchronizing range is equal to initial operating frequency up to 1.4MHz.
PAGE 10
LT3436 U U W U APPLICATIONS INFORMATION L1 3.9µH D1 B220A INPUT 5V C3 4.7µF CERAMIC OPEN OR HIGH = ON LT3436 SHDN SYNC OUTPUT 12V 0.8A† VSW VIN R1 90.9k VC GND FB C2 10nF R3 4.7k C4 470pF C1 22µF CERAMIC R2 10k 1% †MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.
PAGE 11
LT3436 U W U U APPLICATIONS INFORMATION The inductor must have a rating greater than its peak operating current to prevent saturation resulting in efficiency loss. Peak inductor current is given by: thermal resistance number and add in worst-case ambient temperature: (VOUT )(IOUT ) VIN (VOUT − VIN ) + VIN • η 2VOUT (L)(f) Also, consideration should be given to the DC resistance of the inductor. Inductor resistance contributes directly to the efficiency losses in the overall converter.
PAGE 12
LT3436 U TYPICAL APPLICATIO S Load Disconnects in Shutdown D3 1N4148 L1 3.9µH VIN 5V OFF ON D2 1N4148 D1 B220A C5 0.1µF VSW VIN C3 4.7µF C6 0.1µF FB VC C2 10nF R3 4.7k VOUT 12V C7 0.8A 22µF Q1 C1 Si2306DS 4.7µF R1 90.9k LT3436 SHDN SYNC GND R4 1M R2 10k 1% C4 470pF LT3436 • TA02 3V to 20VIN 5VOUT SEPIC with Either Two Inductors or a Transformer D1 B220A L1 CDRH6D28-100 VIN 3V TO 20V + C1 OPT VIN SW C7 1µF, X5R, 25V CERAMIC C5 OPT C6 OPT R1 31.
PAGE 13
LT3436 U TYPICAL APPLICATIO S 4V-9VIN to 5VOUT SEPIC Converter** VIN** 4V TO 9V L1A* 15µH VIN OFF ON VSW SHDN • C1 4.7µF 20V FB GND R2 31.6k 1% C2 4.7µF LT3436 + D1 B220A • VC + L1B* 15µH R1 2.2k C4 15nF R3 10k 1% C5 470pF IOUT 0.84A 1.03A 1.18A 1.29A 1.50A C3 47µF 10V LT3436 • TA03 †MAX I OUT * COILTRONICS CTX15-4 ** INPUT VOLTAGE MAY BE GREATER OR LESS THAN OUTPUT VOLTAGE VOUT† 5V VIN 4V 5V 6V 7V 9V Boost Converter Drives Luxeon III 1A 3.6V White LED with 70% Efficiency 0.
PAGE 14
LT3436 U TYPICAL APPLICATIO S Single Li-Ion Cell to 5V D1 B220A L1 4.7µH VOUT 5V VSW R1 31.6k 1% FB + VIN OFF ON SHDN LT3436 + SINGLE Li-Ion CELL + C1 10µF VC GND C4 47µF 10V R2 10k 1% C2 3.3nF R3 1.5k C3 470pF LT3436 • TA04 IOUT VIN 1.5A 2.7V 1.86A 3.3V 2.0A 3.6V SEPIC Converter Drives 5W LumiLEDs Luxeon V White LEDs at 70% Efficiency D1 B130A L1 VIN 3.6V TO 17V VOUT CCOUP 2.2µF, X5R, 25V CERAMIC D2 L2 VIN LED ON VIN SHDN LT3436 + SW FB – R5 23.7k SYNC VC GND GND C1 4.
PAGE 15
LT3436 U PACKAGE DESCRIPTION FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BB 4.90 – 5.10* (.193 – .201) 3.58 (.141) 3.58 (.141) 16 1514 13 12 1110 6.60 ±0.10 9 2.94 (.116) 4.50 ±0.10 2.94 6.40 (.116) (.252) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.
PAGE 16
LT3436 U TYPICAL APPLICATIO High Voltage Laser Power Supply 0.01µF 5kV 1800pF 10kV 47k 5W 1800pF 10kV 8 11 L1 1 4 5 HV DIODES 3 2 LASER + 2.2µF Q1 0.47µF 150Ω L2 10µH MUR405 VIN 12V TO 25V Q2 VSW 10k VIN + 10k FB LT3436 2.2µF VC 0.1µF VIN 1N4002 (ALL) 190Ω 1% GND + 10µF LT3436 • TA05 L1 = TBD Q1, Q2 = ZETEX ZTX849 0.47µF = WIMA 3X 0.