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Linear Technology Electronic Components Datasheet

LT1938 Datasheet

Step-Down Switching Regulator

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FEATURES
Wide Input Voltage Range: 3.6V to 25V
2.2A Maximum Output Current
Adjustable Switching Frequency: 300kHz to 2.8MHz
Low Shutdown Current: IQ < 1µA
Integrated Boost Diode
Power Good Flag
Saturating Switch Design: 0.18Ω On-Resistance
1.265V Feedback Reference Voltage
Output Voltage: 1.265V to 20V
Soft-Start Capability
Small 10-Pin Thermally Enhanced (3mm × 3mm)
DFN Package
APPLICATIONS
Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
LT1938
25V, 2.2A, 2.8MHz
Step-Down
Switching Regulator
DESCRIPTION
The LT®1938 is an adjustable frequency (300kHz to
2.8MHz) monolithic buck switching regulator that accepts
input voltages up to 25V. A high efficiency 0.18Ω switch
is included on the die along with a boost Schottky diode
and the necessary oscillator, control and logic circuitry.
Current mode topology is used for fast transient response
and good loop stability. The LT1938’s high operating fre-
quency allows the use of small, low cost inductors and
ceramic capacitors resulting in low output ripple while
keeping total solution size to a minimum. The low current
shutdown mode reduces input supply current to less than
1µA while a resistor and capacitor on the RUN/SS pin
provide a controlled output voltage ramp (soft-start). A
power good flag signals when VOUT reaches 90% of the
programmed output voltage. The LT1938 is available in
a 3mm × 3mm DFN package with Exposed Pad for low
thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
VIN
4.5V TO
25V
3.3V Step-Down Converter
4.7µF
OFF ON
16.2k
680pF
VIN
RUN/SS
BD
BOOST
VC SW
LT1938
RT
PG BIAS
60.4k
GND FB
0.47µF 4.7µH
324k
200k
VOUT
3.3V
2.2A
22µF
1938 TA01
Efficiency (VOUT = 3.3V)
90
VIN = 7V
85
80
VIN = 24V
VIN = 12V
75
70
65
60
55 L: NEC PLC-0745-4R7
f = 800kHz
50
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
LOAD CURRENT (A)
1938 G02
1938fa
1


Linear Technology Electronic Components Datasheet

LT1938 Datasheet

Step-Down Switching Regulator

No Preview Available !

LT1938
Absolute Maximum Ratings
(Note 1)
VIN, RUN/SS Voltage..................................................25V
BOOST Pin Voltage....................................................50V
BOOST Pin Above SW Pin..........................................25V
FB, RT, VC Voltage........................................................5V
BIAS, PG, BD Voltage.................................................25V
Operating Junction Temperature Range (Note 2)
LT1938E.............................................. –40°C to 125°C
LT1938I............................................... –40°C to 125°C
Storage Temperature Range.................... –65°C to 150°C
pIN CONFIGURATION
TOP VIEW
BD
BOOST
SW
VIN
RUN/SS
1
2
3
4
5
10 RT
9 VC
11 8 FB
7 BIAS
6 PG
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 45°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
order information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT1938EDD#PBF
LT1938EDD#TRPBF
LDFT
10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT1938IDD#PBF
LT1938IDD#TRPBF
LDFT
10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
E lectrical Characteristics The denotes the specifications which apply over the full operating
temperature
noted. (Note
range,
2)
otherwise
specifications
are
at
TA
=
25°C.
VIN
=
10V,
VRUN/SS
=
10V,
VBOOST
=
15V,
VBIAS
=
3.3V
unless
otherwise
PARAMETER
Minimum Input Voltage
Quiescent Current from VIN
Quiescent Current from BIAS
Minimum Bias Voltage
Feedback Voltage
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
CONDITIONS
VRUN/SS = 0.2V
VBIAS = 3V, Not Switching
VBIAS = 0, Not Switching
VRUN/SS = 0.2V
VBIAS = 3V, Not Switching
VBIAS = 0, Not Switching
4V < VIN < 25V
MIN
1.25
1.24
TYP
3
0.01
0.4
1.2
0.01
0.85
0
2.7
1.265
1.265
30
0.002
MAX
3.6
0.5
0.8
2.0
0.5
1.5
0.1
3
1.28
1.29
100
0.02
UNITS
V
µA
mA
mA
µA
mA
mA
V
V
V
nA
%/V
1938fa
2


Part Number LT1938
Description Step-Down Switching Regulator
Maker Linear
PDF Download

LT1938 Datasheet PDF






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