Datasheet

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LTC3442

3442fb

For more information www.linear.com/LTC3442

TYPICAL APPLICATION

FEATURES DESCRIPTION

Micropower Synchronous

Buck-Boost DC/DC Converter with

Automatic Burst Mode Operation

The LTC

3442 is a highly efficient, fixed frequency, buck-

boost DC/DC converter, which operates from input volt-

ages above, below, and equal to the output voltage. The

topology incorporated in the IC provides a continuous

transfer function through all operating modes, making the

product ideal for a single lithium-ion or

multicell alkaline

applications where the output voltage is within the battery

voltage range.

The device includes two 0.10Ω N-channel MOSFET

switches and two 0.10Ω P-channel switches. Operating

frequency and average input current limit can each be

programmed with an external resistor. Quiescent current

is only 35µA in Burst Mode operation, maximizing battery

life in portable applications. Automatic Burst Mode opera-

tion allows the user to program the

load current for Burst

Mode operation, or to control it manually.

Other features include 1µA shutdown current, program-

mable soft-start, peak current limit and thermal shutdown.

The LTC3442 is available in a low profile, thermally en-

hanced 12-lead (4mm × 3mm × 0.75mm) DFN package.

APPLICATIONS

Regulated Output with Input Voltages Above,

Below, or Equal to the Output

Single Inductor, No Schottky Diodes Required

Manual or Programmable Automatic Burst Mode

Operation

Programmable Average Input Current Limit

Up to 1.2A Continuous Output Current from a Single

Lithium-Ion Cell

High Efficiency: Up to 95%

Output Disconnect in Shutdown

2.4V to 5.5V Input Range

2.4V to 5.25V Output Range

35µA Quiescent Current in Burst Mode Operation

Programmable Frequency from 300kHz to 2MHz

<1µA Shutdown Current

Small, Thermally Enhanced 12-Lead (4mm × 3mm)

DFN Package

PDA/‘SMART’ Phones

Handheld Computers

MP3 Players

Handheld Instruments

Digital Cameras

Wireless Handsets

USB Peripherals

L, LT , LT C , LT M , Linear Technology, the Linear logo and Burst Mode are registered trademarks

and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Protected by U.S. Patents, including 6404251, 6166527.

SW1

SHDN/SS

LIM

SGND

SW2

OUT

BURST

PGND

LTC3442

10µF

0.01µF

2.5V TO

4.2V

Li-Ion

340k

2.2k

22µF

220pF

OUT

3.3V

1.2A

200k

0.01µF

15k

470pF

3442 TA01a

4.7µH

71.5k 200k

(V)

2.5

EFFICIENCY (%)

100

3.0

3.5 4.0 4.5

3442 • TA01b

5.0 5.5

1A LOAD

300mA LOAD

OUT

= 3.3V

L = 4.7µH

F = 600kHz

Efficiency vs V

Summary of content (20 pages)

PAGE 1
LTC3442 Micropower Synchronous Buck-Boost DC/DC Converter with Automatic Burst Mode Operation DESCRIPTION FEATURES n n n n n n n n n n n n n Regulated Output with Input Voltages Above, Below, or Equal to the Output Single Inductor, No Schottky Diodes Required Manual or Programmable Automatic Burst Mode® Operation Programmable Average Input Current Limit Up to 1.2A Continuous Output Current from a Single Lithium-Ion Cell High Efficiency: Up to 95% Output Disconnect in Shutdown 2.4V to 5.
PAGE 2
LTC3442 ABSOLUTE MAXIMUM RATINGS (Notes 1, 4) PIN CONFIGURATION VIN, VOUT Voltage.............................................– 0.3 to 6V SW1, SW2 Voltage DC................................................................ –0.3 to 6V Pulsed <100ns.................................................. –0.3 to 7V SHDN/SS, BURST Voltage................................ –0.3 to 6V RLIM............................................................................VIN Operating Temperature (Note 2).................
PAGE 3
LTC3442 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V, RT = 64.9k, unless otherwise noted (Note 2). PARAMETER Error Amp Sink Current Burst Threshold (Falling) Burst Threshold (Rising) Burst Current Ratio Input Current Ratio RLIM Threshold SHDN/SS Threshold CONDITIONS BURST > 1.25V MIN Ratio of IOUT to IBURST Ratio of IIN to IRLIM, IIN = 0.
PAGE 4
LTC3442 TYPICAL PERFORMANCE CHARACTERISTICS VOUT = 3.3V 6 1MHz 0.70 0.60 0.50 0.40 0.30 0.20 4 2 0 –2 –4 –8 2.5 0 .05 .10 .15 .20 .25 .30 .35 .40 .45 .50 INPUT CURRENT (A) 3.0 3.5 4.5 4.0 5 VOUT DROPS 10% 0 –5 –10 0.50 5.0 3.5 50 45 VIN QUIESCENT CURRENT (µA) 2.0 MHz 3.0 1.5 MHz 2.5 1.0 MHz 2.0 1.5 0.5 MHz 1.0 NO SWITCHING 0.5 35 30 25 20 15 10 3.0 3.5 4.0 VIN (V) 4.5 5.0 0 5.5 2.5 3.0 3.5 4.0 VIN (V) 4.
PAGE 5
LTC3442 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Change vs Temperature (Normalized) Switch Pins Before Entering Boost Mode Feedback Voltage vs Temperature (Normalized) 1.0% 2.0% 0.8% 1.5% VIN = VOUT = 3.3V SW1 2V/DIV 0.6% 1.0% CHANGE FROM 25°C CHANGE FROM 25°C (TA = 25°C unless otherwise specified). 0.5% 0.0% –0.5% –1.0% 0.4% SW2 2V/DIV 0.2% 0.0% –2.0% –0.4% 50ns/DIV VIN = 2.9V VOUT = 3.3V AT 500mA –0.6% –1.5% –0.8% –2.0% –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) –1.
PAGE 6
LTC3442 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise specified). Pulsed Overload Using Average Input Current Limit Transition from Burst Mode Operation to Fixed Frequency Mode VOUT 2V/DIV VOUT 50mV/DIV RLIM PIN 0.5V/DIV INDUCTOR CURRENT 0.5A/DIV INDUCTOR CURRENT 0.5A/DIV 200µs/DIV 1ms/DIV 3442 G22 3442 G23 RLIM = 133k CLIM = .001µF COUT = 100µF LOW ESR TANTALUM PIN FUNCTIONS SHDN/SS (Pin 1): Combined Soft-Start and Shutdown. Applied voltage <0.4V shuts down the IC. Tie to >1.
PAGE 7
LTC3442 BLOCK DIAGRAM SW1 SW2 4 6 SW D SW A 8 SW B SW C – GATE DRIVERS AND ANTICROSS CONDUCTION REVERSE AMP – RLIM 10 0.95V + AV = 6 + AVERAGE ILIM Gm = 1/60k – 3A PEAK CURRENT LIMIT – PWM LOGIC 2.3V – PWM COMPARATORS UVLO 11 VC + + AUTOMATIC BURST MODE CONTROL AND VC HOLD SLEEP 2 12 FB – VIN – 1.22V + 5A + ERROR AMP – + RT OSC 7 VIN SHDN/SS 1 VOUT + VIN 9 SHUTDOWN SOFT-START VCC VREF SS BURST 1.
PAGE 8
LTC3442 OPERATION The LTC3442 provides high efficiency, low noise power for applications such as portable instrumentation. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on VC determines the output duty cycle of the switches. Since VC is a filtered signal, it provides rejection of frequencies from well below the switching frequency.
PAGE 9
LTC3442 OPERATION Reverse Current Limit During fixed frequency operation, the LTC3442 operates in forced continuous conduction mode. The reverse current limit amplifier monitors the inductor current from the output through switch D. Once the negative inductor current exceeds 500mA typical, the IC will shut off switch D. Four-Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor, VIN, VOUT and GND.
PAGE 10
LTC3442 OPERATION Switch A is always on and switch B is always off during this mode. When the internal control voltage, VCI, is above voltage V3, switch pair CD will alternately switch to provide a boosted output voltage. This operation is typical to a synchronous boost regulator. The maximum duty cycle of the converter is limited to 88% typical and is reached when VCI is above V4.
PAGE 11
LTC3442 OPERATION For automatic operation, a filter capacitor should also be connected from BURST to ground to prevent ripple on BURST from causing the IC to oscillate in and out of Burst Mode operation. The equation for the minimum capacitor value is: CBURST(MIN) ≥ COUT • VOUT 60,000 frequency mode, raising VOUT. Once regulation is achieved, the IC will then enter Burst Mode operation once again, and the cycle will repeat, resulting in about 4% output ripple.
PAGE 12
LTC3442 OPERATION ERROR AMP VIN 14µA + VOUT 1.22V R1 FB – 12 VC SOFT-START CLAMP CP1 R2 11 VCI TO PWM COMPARATORS SHDN/SS RSS ENABLE SIGNAL 1 CSS + CHIP ENABLE – 3442 F05 0.7V Figure 5. Soft-Start Circuitry APPLICATIONS INFORMATION COMPONENT SELECTION Inductor Selection The high frequency operation of the LTC3442 allows the use of small surface mount inductors. The inductor ripple current is typically set to 20% to 40% of the maximum inductor current.
PAGE 13
LTC3442 APPLICATIONS INFORMATION For high efficiency, choose a ferrite inductor with a high frequency core material to reduce core loses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses, and must be able to handle the peak inductor current without saturating. Molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1A to 2A region. To minimize radiated noise, use a shielded inductor.
PAGE 14
LTC3442 APPLICATIONS INFORMATION Optional Schottky Diodes The Schottky diodes across the synchronous switches B and D are not required (VOUT < 4.3V), but provide a lower drop during the break-before-make time (typically 15ns) improving efficiency. Use a surface mount Schottky diode such as an MBRM120T3 or equivalent. Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. For applications with an output voltage above 4.
PAGE 15
LTC3442 APPLICATIONS INFORMATION A simple Type I compensation network can be incorporated to stabilize the loop, but at a cost of reduced bandwidth and slower transient response. To ensure proper phase margin using Type I compensation, the loop must be crossed over a decade before the LC double pole. The unity-gain frequency of the error amplifier with the Type I compensation is given by: fUG = the output filter.
PAGE 16
LTC3442 TYPICAL APPLICATIONS Multi-Input 3.3V at 600mA Boost Converter for Portable Applications with Automatic Burst Mode Operation and Average Input Current Limit for USB Powered Devices L1 4.7µH 1nF 2Ω Li-Ion D1 MBRM120T3 2.5V TO 5.5V USB/5V CIN 10µF SW2 LTC3442 VOUT VIN SW1 1M 143k SHDN/SS FB RLIM VC RT 2N7002 0.01µF USB PRESENT RSNUB** 1Ω 1nF 143k BURST SGND 340k 15k 220pF 470pF PGND 64.9k 2.2k COUT 22µF 200k 200k 0.
PAGE 17
LTC3442 TYPICAL APPLICATIONS High Current LED Driver with Low/High Current Range for Pulsed Applications; LED Current Is 0.5A with 1.5A Pulse 3.3µH R5 7.87k VIN 2.7V TO 4.2V SW1 SW2 VIN VOUT VOUT ILED = 500mA/1.5A LTC3442 *OFF ON 10µF 6.3V SHDN/SS FB 1nF RLIM RT R4 2k 57.6k VC R2 20k BURST PGND SGND OPEN LED VOLTAGE LIMIT = (R4 + R5) • 0.95/R4 LOW HI 10µF 6.3V R2 200k 95.3k 1nF 40.2k 2N7002 LHXL-PW03 R1 301k R2 = R1/1.5 ILED = 24 • (R1 + R2 + R3)/(R1 • R3) AMPS (OR: ILED = 40/R3 + .
PAGE 18
LTC3442 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev D) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ±0.10 12 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) 0.
PAGE 19
LTC3442 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 05/13 Modified the Absolute Maximum Ratings section and added new Order Information Modified the Electrical Characteristics table and Note 2 2 2, 3 Simplified Block Diagram, update 1V to 0.95V 7 Changed Operation section, 1V to 0.7V for soft-start 12 3442fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
PAGE 20
LTC3442 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1613 550mA (ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1µA, ThinSOT™ Package LT1618 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD < 1µA, MS10 Package LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.