LT1940L_15 Datasheet, PDF (1/20 Pages) Linear Technology – Dual Monolithic 1.4A, 1.1MHz Step-Down Switching Regulator

FEATURES
s _{Wide Input Voltage Range}
LT1940: 3.6V to 25V
LT1940L: 3.6V to 7V
s _{Two 1.4A Output Switching Regulators with}
Internal Power Switches
s _{Constant 1.1MHz Switching Frequency}
s _{Anti-Phase Switching Reduces Ripple}
s _{Independent Shutdown/Soft-Start Pins}
s _{Independent Power Good Indicators Ease}
Supply Sequencing
s _{Uses Small Inductors and Ceramic Capacitors}
s _{Small 16-Lead Thermally Enhanced}
TSSOP Surface M_Uount Package
APPLICATIO S
s _{Disk Drives}
s _{DSP Power Supplies}
s _{Wall Transformer Regulation}
s _{Distributed Power Regulation}
s _{DSL Modems}
s _{Cable Modems}
, LTC and LT are registered trademarks of Linear Technology Corporation.
LT1940/LT1940L
Dual Monolithic 1.4A,
1.1MHz Step-Down
Switching Regulator
DESCRIPTIO
The LT^®1940 is a dual current mode PWM step-down
DC/DC converter with internal 2A power switches. Both con-
verters are synchronized to a single 1.1MHz oscillator and
run with opposite phases, reducing input ripple current. The
output voltages are set with external resistor dividers, and
each regulator has independent shutdown and soft-start
circuits. Each regulator generates a power-good signal
when its output is in regulation, easing power supply se-
quencing and interfacing with microcontrollers and DSPs.
The LT1940’s 1.1MHz switching frequency allows the use
of tiny inductors and capacitors, resulting in a very small
dual 1.4A output solution. Constant frequency and ceramic
capacitors combine to produce low, predictable output
ripple voltage. With its wide input range of 3.6V to 25V, the
LT1940 regulates a wide variety of power sources, from
4-cell batteries and 5V logic rails to unregulated wall trans-
formers, lead acid batteries and distributed-power supplies.
The LT1940L is intended to operate from regulated 5V
supplies. A current mode PWM architecture provides fast
transient response with simple compensation components
and cycle-by-cycle current limiting. Frequency foldback and
thermal shutdown provide additional protection.
TYPICAL APPLICATIO
V_IN
7V TO 25V
4.7µF
CMDSH-3
V_IN
BOOST1 BOOST2
OUT1
3.3V
1.4A
0.1µF
3.3µH
UPS140
16.5k
LT1940
SW1
SW2
FB1
FB2
CMDSH-3
0.1µF
4.7µH
UPS140
30.1k
OUT2
5V
1.4A
10.0k
15k
V_C1
V_C2
RUN/SS1
PG1
15k
10.0k
10µF
330pF
RUN/SS2
PG2
10µF
1nF
GND
330pF
100k
POWER
1940 F01 GOOD
Figure 1. 3.3V and 5V Dual Output Step-Down Converter with Output Sequencing (LT1940)
Efficiency vs Load Current
100
V_IN = 12V
90
V_OUT = 5V
80
V_OUT = 3.3V
70
60
0
0.5
1.0
LOAD CURRENT (A)
1.5
1940 F01b
1940fa
1