Datasheet LT1940, LT1940L (Analog Devices)

LT1940/LT1940L Dual Monolithic 1.4A, 1.1MHz Step-Down Switching Regulator
U FEATURES DESCRIPTIO
■
Wide Input Voltage Range
The LT®1940 is a dual current mode PWM step-down
LT1940: 3.6V to 25V
DC/DC converter with internal 2A power switches. Both con-
LT1940L: 3.6V to 7V
verters are synchronized to a single 1.1MHz oscillator and ■
Two 1.4A Output Switching Regulators with
run with opposite phases, reducing input ripple current. The
Internal Power Switches
output voltages are set with external resistor dividers, and ■
Constant 1.1MHz Switching Frequency
each regulator has independent shutdown and soft-start ■
Anti-Phase Switching Reduces Ripple
circuits. Each regulator generates a power-good signal ■ Independent Shutdown/Soft-Start Pins when its output is in regulation, easing power supply se- ■ Independent Power Good Indicators Ease quencing and interfacing with microcontrollers and DSPs. Supply Sequencing The LT1940’s 1.1MHz switching frequency allows the use ■ Uses Small Inductors and Ceramic Capacitors of tiny inductors and capacitors, resulting in a very small ■ Small 16-Lead Thermally Enhanced dual 1.4A output solution. Constant frequency and ceramic TSSOP Surface Mount Package
U
capacitors combine to produce low, predictable output
APPLICATIO S
ripple voltage. With its wide input range of 3.6V to 25V, the LT1940 regulates a wide variety of power sources, from ■ Disk Drives 4-cell batteries and 5V logic rails to unregulated wall trans- ■ DSP Power Supplies formers, lead acid batteries and distributed-power supplies. ■ Wall Transformer Regulation The LT1940L is intended to operate from regulated 5V ■ Distributed Power Regulation supplies. A current mode PWM architecture provides fast ■ DSL Modems transient response with simple compensation components ■ Cable Modems and cycle-by-cycle current limiting. Frequency foldback and , LTC and LT are registered trademarks of Linear Technology Corporation. thermal shutdown provide additional protection.
U TYPICAL APPLICATIO
VIN 7V TO 25V 4.7µF V CMDSH-3 IN CMDSH-3
Efficiency vs Load Current
OUT2 BOOST1 BOOST2 5V 100 1.4A VIN = 12V 0.1µF LT1940 0.1µF 3.3 OUT1 µH 4.7µH 3.3V SW1 SW2 90 1.4A VOUT = 5V UPS140 UPS140 16.5k 30.1k 80 FB1 FB2 VOUT = 3.3V V EFFICIENCY (%) C1 VC2 70 10.0k 15k RUN/SS1 PG1 15k 10.0k 10µF 330pF RUN/SS2 PG2 10µF 60 GND 330pF 100k 1nF 0 0.5 1.0 1.5 LOAD CURRENT (A) POWER 1940 F01b 1940 F01 GOOD
Figure 1. 3.3V and 5V Dual Output Step-Down Converter with Output Sequencing (LT1940)
1940fa 1