Datasheet

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LTC3127

3127f

Typical applicaTion

DescripTion

1A Buck-Boost DC/DC

Converter with Programmable

Input Current Limit

The LTC

3127 is a wide V

range, highly efficient, 1.35MHz

fixed frequency buck-boost DC/DC converter that operates

from input voltages above, below or equal to the output

voltage. The LTC3127 features programmable average

input current limit, making it ideal for power-limited input

sources. The input current limit is programmed with a

single resistor and is accurate from 0.2A to 1A of average

input current.

The topology incorporated provides a continuous

transfer function through all operating modes. Other

features include <1μA shutdown current, pin-selectable

Burst Mode operation and thermal overload protection.

The LTC3127 is housed in thermally enhanced 10-lead

(3mm × 3mm × 0.75mm) DFN packages and 12-lead

MSOP packages.

Efficiency vs V

FeaTures

applicaTions

Programmable (0.2A to 1A) ±4% Accurate Average

Input Current Limit

Regulated Output with Input Voltages Above,

Below or Equal to the Output

1.8V to 5.5V (Input) and 1.8V to 5.25V (Output)

Voltage Range

0.6A Continuous Output Current: V

> 1.8V

1A Continuous Output Current: V

> 3V

Single Inductor

Synchronous Rectification: Up to 96% Efficiency

Burst Mode

Operation: I

= 35μA (Pin Selectable)

Output Disconnect in Shutdown

<1μA Shutdown Current

Small, Thermally Enhanced 10-Lead (3mm × 3mm ×

0.75mm) DFN and 12-Lead MSOP Packages

USB Powered GSM Modems

Supercap Charger

Handheld Test Instruments

PC Card Modems

Wireless Terminals

ONOFF

USB OR Li-Ion

2.9V to 5.5V

10µF

L1: COILCRAFT XPL4020-472ML

32.4k

4.7µH

182k

320k

2.2mF

OUT

3.3V

499k

SW1

MODE

SHDN

PROG

SGND PGND

SW2

OUT

3127 TA01

100pF

(V)

2.5

EFFICIENCY (%)

100

3127 TA01a

5 5.54.53.53

300mA LOAD

OUT

= 3.3V

L = 4.7µH

F = 1.35MHz

1A LOAD

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

and PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

USB or Li-Ion (500mA Maximum Input Current) to 3.3V

Summary of content (20 pages)

PAGE 1
LTC3127 1A Buck-Boost DC/DC Converter with Programmable Input Current Limit Description Features n n n n n n n n n n n Programmable (0.2A to 1A) ±4% Accurate Average Input Current Limit Regulated Output with Input Voltages Above, Below or Equal to the Output 1.8V to 5.5V (Input) and 1.8V to 5.25V (Output) Voltage Range 0.6A Continuous Output Current: VIN > 1.
PAGE 2
LTC3127 Absolute Maximum Ratings (Note 1) VIN , VOUT Voltage .......................................... –0.3 to 6V SW1, SW2 DC Voltage.................................... –0.3 to 6V SW1, SW2 Pulsed (<100ns) Voltage............... –0.3 to 7V MODE, FB, VC Voltage..................................... –0.3 to 6V SHDN Voltage ................................................ –0.3 to 6V PROG Voltage................................................. –0.3 to 6V Operating Junction Temperature Range (Note 2)........
PAGE 3
LTC3127 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VIN = 3.6V, VOUT = 3.3V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Input Operating Range l 1.8 5.5 V Output Voltage Adjust l 1.8 5.25 V Feedback Voltage l 1.165 1.195 1.225 V 1 50 nA Feedback Input Current VFB = 1.25V Quiescent Current—Burst Mode Operation VFB > 1.
PAGE 4
LTC3127 Typical Performance Characteristics PWM 90 80 BURST 80 70 70 60 50 40 30 20 VIN = 1.8V VIN = 3.6V VIN = 5V 10 0 0.1 1 10 100 LOAD CURRENT (mA) 50 PWM 40 –2 –3 –4 3.4 3.8 4.2 4.6 VIN (V) VIN = 2.9V VIN = 3.6V VIN = 4.3V 1 10 100 LOAD CURRENT (mA) 5 5.4 VIN = 4.5V VIN = 5V VIN = 5.5V 10 0 0.1 1000 1 10 100 1000 LOAD CURRENT (mA) 3127 G02 10000 3127 G03 Quiescent Current vs VIN (Fixed Frequency Mode–Not Switching) 430 VOUT = 3.3V RPROG = 32.
PAGE 5
LTC3127 Typical Performance Characteristics Feedback Voltage vs Temperature (Normalized) 0.40 L = 4.7µH VOUT = 3.3V VIN = 3.6V NMOS RDS(ON) vs VIN 300 VOUT = 3.3V 0.30 0.20 –0.20 –0.40 –0.60 250 0.10 RDS(ON) (mΩ) CHANGE (%) 0.00 VOUT Regulation vs Load Current (Normalized) VOUT REGULATION (%) 0.20 (TJ = 25°C, unless otherwise noted ) 0 –0.10 –0.20 –0.30 200 SWC 150 –0.40 SWB –0.50 –0.80 –50 –30 50 –10 10 30 TEMPERATURE (°C) 70 –0.
PAGE 6
LTC3127 Typical Performance Characteristics Load Transient Response in Burst Mode Operation, No Load to 1A, Not in Input Current Limit ILOAD 1A/DIV (TJ = 25°C, unless otherwise noted ) Transition from Burst Mode Operation to Fixed Frequency Mode IIN 200mA/DIV IIN 1A/DIV VOUT 50mV/DIV VOUT 20mV/DIV MODE 5V/DIV 200µs/DIV VIN = 3.6V RPROG = 90k R3 = 499k 3127 G17 MODE 5V/DIV 100µs/DIV VOUT = 3.3V COUT = 4.4mF C1 = 100pF 3127 G18 VOUT = 3.3V VIN = 3.6V RPROG = 32.4k COUT = 4.
PAGE 7
LTC3127 Pin Functions (DD Package) SW1 (Pin 1): Switch Pin Where Internal Switches A and B Are Connected. Connect inductor from SW1 to SW2. Minimize trace length to reduce EMI. SGND (Pin 6): Signal Ground for the IC. Terminate the PROG resistor, compensation components and the output voltage divider to SGND. VIN (Pin 2): Input Supply Pin. Internal VCC for the IC. A 10μF or greater ceramic capacitor should be placed as close to VIN and PGND as possible. FB (Pin 7): Feedback Pin.
PAGE 8
LTC3127 Block Diagram SW1 L SW2 VIN VOUT CIN – + VC IZERO AMP IPEAK AMP PWM COMPARATOR AND LOGIC SHDN MODE PROG RPROG SAMPLE/HOLD AND RESET R2 + – FB + 1.
PAGE 9
LTC3127 Operation The LTC3127 is an average input current controlled buckboost DC/DC converter offered in both a thermally enhanced 3mm × 3mm DFN package and a thermally enhanced 12lead MSOP package. The buck-boost converter utilizes a proprietary switching algorithm which allows its output voltage to be regulated above, below or equal to the input voltage. The low RDS(ON), low gate charge synchronous switches efficiently provide high frequency PWM control.
PAGE 10
LTC3127 Operation Integral compensation is required if an output capacitor less than 1000µF but greater than 44µF is used, otherwise using proportional compensation is recommended. When compensating the converter with integral compensation it is important to consider that the total bandwidth of the network must be below 15kHz. The inner current loop of the LTC3127 eliminates one of the double poles caused by the inductor.
PAGE 11
LTC3127 Operation The input current limit is set by the RPROG resistor placed on the PROG pin to SGND. The resistor value can be calculated using the following formula: RPROG = 54.92 • ILIMIT (A) + 4.94 (kΩ) Where ILIMIT is the average input current limit in amps. A secondary 2.5A (typical) current limit forces switches B and D on and A and C off if tripped. This current limit is not affected by the value of RPROG.
PAGE 12
LTC3127 Applications Information A typical LTC3127 application circuit is shown on the front page of this data sheet. The external component selection is determined by the desired output voltage, input current and ripple voltage requirements for each particular application. However, basic guidelines and considerations for the design process are provided in this section.
PAGE 13
LTC3127 Applications Information Output and Input Capacitor Selection When selecting output capacitors for large pulsed loads, the magnitude and duration of the pulse current, together with the droop voltage specification, determine the choice of the output capacitor. Both the ESR of the capacitor and the charge stored in the capacitor each cycle contribute to the output voltage droop.
PAGE 14
LTC3127 Applications Information Capacitor Selection Example In this example, a pulsed load application requires that VOUT droops less than 300mV. The application is a Li-Ion battery input to a 3.6V output. The pulsed load is a no-load to a 1.5A step with a frequency of 217Hz and a duty cycle of 12.5%. The input current limit is set to 500mA. In order to meet the 300mV droop requirement, the amount of capacitance must be calculated at the highest VIN to VOUT step-up ratio.
PAGE 15
LTC3127 Applications Information PCB Layout Considerations The LTC3127 switches large currents at high frequencies. Special care should be given to the PCB layout to ensure stable, noise-free operation. Figure 4 depicts the recommended PCB layout to be utilized for the LTC3127. A few key guidelines follow: 1. All circulating high current paths should be kept as short as possible. This can be accomplished by keeping the routes to all bold components in Figure 4 as short and as wide as possible.
PAGE 16
LTC3127 Typical Applications USB (500mA Max), 3.8V GSM Pulsed Load L1 4.7µH SW1 VIN VIN USB SW2 VOUT VOUT 3.8V MODE PWM BURST 2.15M LTC3127 OFF ON FB SHDN 10µF C2 2.2mF 1M VC PROG SGND PGND 100pF 32.4k C1, C2: VISHAY TANTAMOUNT TANTALUM, LOW ESR CAPACITORS L1: COILCRAFT XPL4020-472ML C1 2.2mF 499k 3127 TA02 PCMCIA/Compact Flash (3.3V or 5V/500mA Max), 3.8V GPRS, Class 10 Pulsed Load L1 4.7µH SW1 VIN VIN 3.3V OR 5V SW2 VOUT 2.
PAGE 17
LTC3127 Typical Applications Stacked Supercapacitor Charger (1000mA Max Input Current) L1 4.7µH VIN 1.8V to 5.5V SW1 VIN PWM BURST MODE SW2 VOUT 3.16M LTC3127 FB SHDN OFF ON VC PROG 10µF VOUT 5V SGND 1M 100k C2 100F PGND 100pF 60.4k 100k C1 100F 499k L1: COILCRAFT XPL4020-472ML 3127 TA04 General Purpose Forced Continuous Conduction Application with 500µs Start-Up L1 4.7µH SW1 VIN VIN 3V TO 4.3V SW2 VOUT VOUT 3.3V 316k 33pF MODE PWM BURST FB SHDN OFF ON PROG SGND 10µF 0.
PAGE 18
LTC3127 Package Description DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev B) 0.70 p0.05 3.55 p0.05 1.65 p0.05 2.15 p0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.38 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p0.10 (4 SIDES) R = 0.125 TYP 6 0.40 p 0.10 10 1.65 p 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 p0.05 0.00 – 0.05 5 1 (DD) DFN REV B 0309 0.25 p 0.05 0.50 BSC 2.38 p0.
PAGE 19
LTC3127 Package Description MSE Package 12-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1666 Rev B) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 p 0.102 (.112 p .004) 5.23 (.206) MIN 2.845 p 0.102 (.112 p .004) 0.889 p 0.127 (.035 p .005) 6 1 1.651 p 0.102 3.20 – 3.45 (.065 p .004) (.126 – .136) 0.12 REF 12 0.65 0.42 p 0.038 (.0256) (.0165 p .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 4.039 p 0.102 (.159 p .
PAGE 20
LTC3127 Typical Application Single Supercapacitor Charger (1000mA Max Input Current) L1 4.7µH SW1 VIN VIN 1.8V TO 5V SW2 VOUT VOUT 2.5V 1.05M MODE PWM BURST LTC3127 SHDN OFF ON PROG 10µF SGND C1: COOPER BUSSMANN POWERSTOR B-SERIES, B1860-2R5107-R L1: COILCRAFT XPL4020-472ML PGND 60.4k FB 1M VC 100pF C1 100F 499k 3127 TA06 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC3101 Wide VIN, 1MHz Multioutput DC/DC Converter and PowerPath™ Controller 95% Efficiency, VIN: 1.8V to 5.