LT3503
1A, 2.2MHz Step-Down
Switching Regulator in
2mm
×
3mm DFN
FEATURES
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DESCRIPTIO
Wide Input Range: 3.6V to 20V
5V at 1.2A from 11V to 18V Input
5V at 1A from 7.2V to 18V Input
3.3V at 1.2A from 8.5V to 12V Input
3.3V at 1A from 5.5V to 12V Input
Fixed Frequency Operation: 2.2MHz
Output Adjustable Down to 780mV
Short-Circuit Robust
Uses Tiny Capacitors and Inductors
Soft-Start
Internally Compensated
Low Shutdown Current: <2µA
Low V
CESAT
Switch: 400mV at 1A
Thermally Enhanced, 2mm
×
3mm 6-Pin DFN
Low Profile Package
The LT
®
3503 is a current mode PWM step-down DC/DC
converter with an internal 1.45A power switch. The wide
operating input range of 3.6V to 20V makes the LT3503
ideal for regulating power from a wide variety of sources.
Its high operating frequency allows the use of tiny, low
cost inductors and ceramic capacitors, resulting in low,
predictable output ripple.
Cycle-by-cycle current limit provides protection against
shorted outputs and soft-start eliminates input current
surge during start-up. The low current (<2µA) shutdown
mode provides output disconnect, enabling easy power
management in battery-powered systems.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Automotive Battery Regulation
Industrial Control Supplies
Wall Transformer Regulation
Distributed Supply Regulation
Battery-Powered Equipment
TYPICAL APPLICATIO
3.3V Step-Down Converter
85
V
IN
4.5V TO 12V
20V MAX
ON OFF
V
IN
SHDN
BOOST
LT3503
SW
37.4k
GND
1µF
FB
11.5k
120pF
10µF
0.1µF 2.5µH
V
OUT
3.3V
1A, V
IN
> 5.5V
1.2A, V
IN
> 8.5V
EFFICIENCY (%)
3503 TA01a
U
Efficiency
V
IN
= 12V
80
75
70
65
60
55
50
0
0.2
0.8
0.6
0.4
LOAD CURRENT (A)
1.0
1.2
3503 TA01b
U
U
3503f
1
LT3503
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
FB 1
GND 2
BOOST 3
7
6 SHDN
5 V
IN
4 SW
Input Voltage (V
IN
) .................................................. 20V
BOOST Pin Voltage .................................................. 40V
BOOST Pin Above SW Pin ....................................... 20V
SHDN Pin ................................................................ 20V
FB Voltage ................................................................. 6V
Operating Temperature Range (Note 2) ... –40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
DCB PACKAGE
6-LEAD (2mm
´
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 64°C/ W
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3503EDCB
DCB PART MARKING
LCGW
Order Options
Tape and Reel: Add #TR Lead Free: Add #PBF
Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 12V, V
BOOST
= 17V, unless otherwise noted. (Note 2)
PARAMETER
V
IN
Operating Range
Undervoltage Lockout
Feedback Voltage
FB Pin Bias Current
Quiescent Current
Quiescent Current in Shutdown
Reference Line Regulation
Switching Frequency
Maximum Duty Cycle
V
FB
= Measured V
REF
(Note 4)
Not Switching
V
SHDN
= 0V
V
IN
= 5V to 20V
V
FB
= 0.7V
V
FB
= 0V
●
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CONDITIONS
MIN
3.6
3.0
765
TYP
3.4
780
50
1.9
0.01
0.007
MAX
20
3.6
795
150
2.6
2
2.4
UNITS
V
V
mV
nA
mA
µA
%/V
MHz
kHz
%
2.0
76
2.2
36
81
2
U
3503f
W
U
U
W W
W
LT3503
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 12V, V
BOOST
= 17V, unless otherwise noted. (Note 2)
PARAMETER
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Minimum Boost Voltage Above Switch
BOOST Pin Current
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Bias Current
V
SHDN
= 2.3V (Note 5)
V
SHDN
= 0V
6
0.01
I
SW
= 1A
I
SW
= 1A
2.3
0.3
15
0.1
2
25
CONDITIONS
(Note 3)
I
SW
= 1A
MIN
1.45
TYP
1.75
400
2
2.3
50
MAX
2.2
UNITS
A
mV
µA
V
mA
V
V
µA
µA
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT3503E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
Note 4:
Current flows out of pin.
Note 5:
Current flows into pin.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency (V
OUT
= 3.3V)
90
88
86
V
IN
= 8V
V
IN
= 12V
L = 2.5µH
EFFICIENCY (%)
EFFICIENCY (%)
84
82
80
78
76
74
72
70
0
0.2
0.6
0.8
0.4
LOAD CURRENT (A)
1.0
1.2
3503 G01
U W
T
A
= 25°C unless otherwise noted.
Efficiency (V
OUT
= 5V)
90
88
86
84
82
80
78
76
74
72
70
0
L = 3.3µH
V
IN
= 12V
V
IN
= 16V
0.2
0.6
0.8
0.4
LOAD CURRENT (A)
1.0
1.2
3503 G02
3503f
3
LT3503
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Load Current
1.8
1.8
1.6
V
OUT
= 3.3V
1.6 L = 2.2µH
OUTPUT CURRENT (A)
TYPICAL
1.4
OUTPUT CURRENT (A)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
4
5
6
8
9
7
10
INPUT VOLTAGE (V)
11
12
MINIMUM
V
CE(SWITCH)
(mV)
Undervoltage Lockout
4.00
3.90
3.80
3.70
2.75
SWITCHING FREQUENCY (MHz)
UVLO (V)
3.60
3.50
3.40
3.30
3.20
3.10
3.00
–45
–25
35
55
–5
15
TEMPERATURE (°C)
75
3503 G08
Frequency Foldback
2.5
SWITCHING FREQUENCY (MHz)
2.0
1.8
SWITCH CURRENT LIMIT (A)
2.0
1.5
1.0
0.5
0
0
100 200 300 400 500 600 700 800
FEEDBACK VOLTAGE (mV)
3503 G10
4
U W
3503 G03
T
A
= 25°C unless otherwise noted.
Switch Voltage Drop
500
450
400
350
300
250
200
150
100
50
T
A
= 85°C
T
A
= 25°C
Maximum Load Current
V
OUT
= 5V
L = 3.3µH
TYPICAL
1.2
MINIMUM
1.0
0.8
0.6
0.4
0.2
0
6
7
8
9 10 11 12 13
INPUT VOLTAGE (V)
14
15
T
A
= –45°C
0
0
300
900
1200
600
SWITCH CURRENT (mA)
1500
3503 G07
3503 G04
Switching Frequency
2.50
2.25
2.00
1.75
–45
–25
–5
55
15
35
TEMPERATURE (°C)
75
3503 G09
Soft-Start
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.25 0.50 0.75 1 1.25 1.50 1.75
SHDN PIN VOLTAGE (V)
2
3503 G11
3503f
LT3503
TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Pin Current
50
45
40
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
5.0
7.2
5.5
35
I
SHDN
(µA)
30
25
20
15
10
5
0
0
2
4
6
8 10 12 14 16 18 20
V
SHDN
(V)
3503 G12
Switch Current Limit
2.0
1.9
SWITCH CURRENT LIMIT (A)
SWITCH CURRENT LIMIT (A)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
–45
–25
-5
15
35
55
TEMPERATURE (°C)
75
!# ! / #
U W
T
A
= 25°C unless otherwise noted.
Typical Minimum Input Voltage
(V
OUT
= 5V)
7.7
Typical Minimum Input Voltage
(V
OUT
= 3.3V)
6.7
4.5
6.2
4.0
5.7
3.5
1
10
1OO
LOAD CURRENT (mA)
1000
3503 G13
5.2
1
10
100
LOAD CURRENT (mA)
1000
3503 G14
Switch Current Limit
1.8
1.7
1.6
TYPICAL
1.5
1.4
1.3
MINIMUM
1.2
1.1
1.0
0
20
40
60
DUTY CYCLE (%)
80
100
3503 G16
3503f
5
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