LT1941 Datasheet, PDF (1/24 Pages) Linear Technology – Triple Monolithic Switching Regulator

FEATURES
s _{Wide Input Range: 3.5V to 25V}
s _{Three Switching Regulators with Internal Power}
Switches: 3A Step-Down, 2A Step-Down,
1.5A Inverting/Boost
s _{Antiphase Switching Reduces Ripple}
s _{Independent Shutdown/Soft-Start Pins}
s _{Independent Power Good Indicators Ease Supply}
Sequencing
s _{Input Voltage Power Good Indicators Monitor Input}
Supply
s _{Uses Small Inductors and Ceramic Capacitors}
s _{Constant 1.1MHz Switching Frequency}
s _{Thermally Enhanced 28-Lead TSSOP Package}
U
APPLICATIO S
s _{Cable Modems}
s _{DSL Modems}
s _{Distributed Power Regulation}
s _{Wall Transformer Regulation}
s _{Disk Drives}
s _{DSP Power}
, LTC and LT are registered trademarks of Linear Technology Corporation.
LT1941
Triple Monolithic
Switching Regulator
DESCRIPTIO
The LT^®1941 is a triple current mode DC/DC converter
with internal power switches. Two of the regulators are
step-down converters with 3A and 2A power switches.
The third regulator can be configured as a boost, inverter
or SEPIC converter and has a 1.5A power switch. All three
converters are synchronized to a 1.1MHz oscillator. The
two step-down converters 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 regu-
lator generates a power good signal when its output is in
regulation, easing power supply sequencing and interfac-
ing with microcontrollers and DSPs.
The high switching frequency offers several advantages
by permitting the use of small inductors and ceramic
capacitors. Small inductors and capacitors lead to a very
small triple output solution. The constant switching fre-
quency, combined with low impedance ceramic capaci-
tors, result in low, predictable output ripple. With its wide
input voltage range of 3.5V to 25V, the LT1941 regulates
a broad array of power sources from 4-cell batteries and
5V logic rails to unregulated wall transformers, lead acid
batteries and distributed-power supplies.
TYPICAL APPLICATIO
V_IN
4.7V TO 14V
5GOOD
12GOOD
V_OUT1
1.8V
2.4A
V_OUT3*
–12V
350mA
10µF
V_OUT1
V_OUT2
130k 100k
PGOOD1
5GOOD PGOOD2
12GOOD PGOOD3
3µH
33µF
0.22µF
13.7k
3300pF
7.32k 3.3k
1.5nF
BOOST1 BOOST2
LT1941
SW1
SW2
FB1
FB2
V_C1
V_C2
RUNSS1 RUNSS2
22µH _1µF
SW3
BIAS1
NFB
BIAS2
22µH
10µF
133k 13.7k
V_C3
FB3
RUNSS3
GND
100k 100k 100k
0.22µF
1000pF
10.7k
10k 2.49k
1.5nF
3.3µH
22µF
22nF
1.5k
1.5nF
*240mA AT V_IN = 5V, 550mA AT V_IN = 12V
1941 F01
PGOOD1
PGOOD2
PGOOD3
V_OUT2
3.3V
1.4A
Figure 1. Triple Output Power Supply: 3.3V, 1.8V, –12V
RUN/SS
2V/DIV
V_OUT1
2V/DIV
V_OUT2
5V/DIV
V_OUT3
10V/DIV
I_VIN(AVE)
1A/DIV
PGOOD2
5V/DIV
Start-Up Waveforms
with Sequencing
1941 F01b
1941f
1