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Linear Technology Electronic Components Datasheet

LT1940L Datasheet

1.1MHz Step-Down Switching Regulator

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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 MUount 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
VIN
7V TO 25V
4.7µF
CMDSH-3
VIN
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
VC1
RUN/SS1
VC2
PG1
15k 10.0k
10µF
10µF
330pF
1nF
RUN/SS2
PG2
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
VIN = 12V
90
VOUT = 5V
80
VOUT = 3.3V
70
60
0
0.5 1.0
LOAD CURRENT (A)
1.5
1940 F01b
1940fa
1


Linear Technology Electronic Components Datasheet

LT1940L Datasheet

1.1MHz Step-Down Switching Regulator

No Preview Available !

LT1940/LT1940L
ABSOLUTE AXI U RATI GS
(Note 1)
VIN Voltage
LT1940 .................................................... (–0.3), 25V
LT1940L ................................................... (–0.3), 7V
BOOST Pin Voltage
LT1940 ................................................................ 35V
LT1940L ............................................................. 16V
BOOST Pin Above SW Pin
LT1940 ................................................................ 25V
LT1940L ............................................................. 16V
PG Pin Voltage
LT1940 ................................................................ 25V
LT1940L ............................................................... 7V
SW Voltage ................................................................VIN
RUN/SS, FB Pins ...................................................... 6V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) ...–40°C to 85°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UW U
PACKAGE/ORDER I FOR ATIO
BOOST1 1
SW1 2
VIN
VIN
VIN
VIN
SW2
3
4
5
6
7
BOOST2 8
TOP VIEW
16 FB1
15 VC1
14 PG1
13 RUN/SS1
17
12 RUN/SS2
11 PG2
10 VC2
9 FB2
ORDER PART
NUMBER
LT1940EFE
LT1940LEFE
FE PART
MARKING
FE PACKAGE
16-LEAD PLASTIC TSSOP
EXPOSED PAD (PIN 17) IS GND
MUST BE SOLDERED TO PCB
TJMAX = 125°C, θJA = 45°C/W, θJC = 10°C/W
1940EFE
1940LEFE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VBOOST = 8V unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Minimum Operating Voltage
q
3.4 3.6
V
Quiescent Current
Not Switching
3.8 4.8
mA
Shutdown Current
Feedback Voltage
VRUNSS = 0V
0°C to 70°C
–40°C to 85°C
1.230
q 1.225
q 1.215
30
1.250
1.250
1.250
45
1.270
1.270
1.270
µA
V
V
V
FB Pin Bias Current
Reference Line Regulation
Error Amp GM
VFB = 1.25V, VC = 0.4V
LT1940: VIN 5V to 25V
LT1940L: VIN 4V to 7V
q
240 1200
nA
0.005
0.005
%/V
%/V
330 uMhos
Error Amp Voltage Gain
180
VC Source Current
VC Sink Current
VFB = 1V
VFB = 1.5V
42 µA
60 µA
VC Pin to Switch Current Gain
VC Switching Threshold
VC Clamp Voltage
Switching Frequency
VFB = 1.1V
2.4
0.75
1.8
1 1.1 1.25
q 0.95 1.1 1.35
A/V
V
V
MHz
MHz
Switching Phase
150 180 210
Deg
Maximum Duty Cycle
q 78
88
%
Frequency Shift Threshold on FB
fSW = 1MHz
0.5 V
1940fa
2


Part Number LT1940L
Description 1.1MHz Step-Down Switching Regulator
Maker Linear
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LT1940L Datasheet PDF






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