LT1941_15 Datasheet, PDF (1/24 Pages) Linear Technology – Triple Monolithic Switching Regulator

FEATURES
n _{Wide Input Range: 3.5V to 25V}
n _{Three Switching Regulators with Internal Power}
Switches: 3A Step-Down, 2A Step-Down,
1.5A Inverting/Boost
n _{Antiphase Switching Reduces Ripple}
n _{Independent Shutdown/Soft-Start Pins}
n _{Independent Power Good Indicators Ease Supply}
Sequencing
n _{Input Voltage Power Good Indicators Monitor Input}
Supply
n _{Uses Small Inductors and Ceramic Capacitors}
n _{Constant 1.1MHz Switching Frequency}
n _{Thermally Enhanced 28-Lead TSSOP Package}
APPLICATIONS
n _{Cable Modems}
n _{DSL Modems}
n _{Distributed Power Regulation}
n _{Wall Transformer Regulation}
n _{Disk Drives}
n _{DSP Power}
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
LT1941
Triple Monolithic
Switching Regulator
DESCRIPTION
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 phase,
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 sequencing and
interfacing with microcontrollers and DSPs.
The high switching frequency offers several advantages
by permitting the use of small inductors and ceramic
capacitors, leading to a very small triple output solution.
The constant switching frequency, combined with low
impedance ceramic capacitors, 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 APPLICATION
V_IN
4.7V TO 14V
5GOOD
12GOOD
V_OUT1
1.8V
2.4A
V_OUT3
–12V
350mA*
10μF
V_OUT1
V_OUT2
3μH
33μF
13.7k
7.32k
22μH _1μF
22μH
10μF
130k 100k
0.22μF
3300pF
3.3k
1.5nF
133k 13.7k
V_IN
PGOOD1
5GOOD PGOOD2
12GOOD PGOOD3
BOOST1 BOOST2
LT1941
SW1
SW2
FB1
FB2
V_C1
V_C2
RUNSS1 RUNSS2
SW3
BIAS1
NFB
BIAS2
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
Figure 1. Triple Output Power Supply: 3.3V, 1.8V, –12V
1941 F01
PGOOD1
PGOOD2
PGOOD3
V_OUT2
3.3V
1.4A
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
2ms/DIV
1941 F01b
1941fb
1