Document
LTC3125
1.2A Synchronous Step-Up DC/DC Converter with Input Current Limit
FEATURES
n Programmable Average Input Current Limit n 5% Input Current Accuracy n 200mA to 1000mA Program Range n VIN: 1.8V to 5.5V, VOUT: 2V to 5.25V n Supports High Current GSM/GPRS Load Burst n VIN > VOUT Operation n 1.6MHz Fixed Frequency Operation n Internal Current Sense Resistor n 1.2A Peak Current Limit n Up to 93% Efficiency n Output Disconnect in Shutdown n Soft-Start n Low Quiescent Current Burst Mode® Operation n Available in 2mm × 3mm × 0.75mm DFN Package
APPLICATIONS
n GSM/GPRS PCMCIA/CompactFlash PC Card Modems n Wireless Emergency Locators n Portable Radios n Supercap Chargers
DESCRIPTION
The LTC®3125 is a high efficiency, synchronous step-up DC/DC converter with an accurate programmable average input current limit. The resistor programmable average input current limit is 5% accurate at 500mA and is suitable for a wide variety of applications. In mobile computing, GSM and GPRS cards demand high current pulses well beyond the capability of the PC Card and CompactFlash slots. The LTC3125 in concert with a reservoir capacitor, keeps the slot power safely within its capabilities providing a high performance and simple solution.
Synchronous rectification produces high efficiency while the 1.6MHz switching frequency minimizes the solution footprint. The current mode PWM design is internally compensated. Output disconnect allows the load to discharge in shutdown, while also providing inrush current limiting.
Other features include a <1μA shutdown current, shortcircuit and thermal overload protection. The LTC3125 is offered in a low profile 0.75mm × 2mm × 3mm package.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
POWER LOSS (W)
TYPICAL APPLICATION
PCMCIA/CompactFlash (3.3V/500mA Max), 4V GSM Pulsed Load
2.2μH
VIN 3.3V
500mA
10μF CER
OFF ON
CS SW VIN VOUT
LTC3125 SHDN
44.2k
PROG
FB
GND
1.24M 536k
VOUT 4V 2A PULSED LOAD
2200μF s2 TANT
3125 TA01a
EFFICIENCY (%)
Efficiency vs Load Current
100 90 80 70 60 50 40 30 20 10 0 0.001
1
0.1
0.01
VOUT = 4V
VIN = 3.3V
VIN = 2.4V
0.001
0.01 0.1
1
LOAD CURRENT (A)
3125 TA01b
3125fa
1
LTC3125
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, VOUT Voltage ......................................... –0.3V to 6V SW Voltage .................................................. –0.3V to 6V SW Voltage < 100ns .................................... –0.3V to 7V All Other Pins ............................................... –0.3V to 6V Operating Junction Temperature Range (Notes 2, 5)............................................ –40°C to 125°C Junction Temperature ........................................... 125°C Storage Temperature Range................... –65°C to 125°C
PIN CONFIGURATION
TOP VIEW
GND 1
8 SW
FB 2 9 7 VOUT
PROG 3
6 SHDN
VIN 4
5 CS
DCB PACKAGE 8-LEAD (2mm s 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 64°C/W.