LT3502/LT3502A
1.1MHz/2.2MHz, 500mA
Step-Down Regulators in
2mm
×
2mm DFN
FEATURES
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DESCRIPTION
The LT
®
3502/LT3502A are current mode PWM step-down
DC/DC converters with an internal 500mA power switch,
in a tiny 8-lead 2mm
×
2mm DFN package. The wide input
voltage range of 3V to 40V makes the LT3502/LT3502A
suitable for regulating power from a wide variety of sources,
including 24V industrial supplies and automotive batteries.
Its high operating frequency allows the use of tiny, low
cost inductors and capacitors, resulting in a very small
solution. Constant frequency above the AM band avoids
interfering with radio reception, making the LT3502A
particularly suitable for automotive applications.
Cycle-by-cycle current limit and frequency foldback pro-
vide protection against shorted outputs. Soft-start and
frequency foldback eliminates input current surge during
start-up. DA current sense provides further protection in
fault conditions. An internal boost diode reduces com-
ponent count.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
3V to 40V Input Voltage Range
500mA Output Current
Switching Frequency: 2.2MHz (LT3502A),
1.1MHz (LT3502)
800mV Feedback Voltage
Short-Circuit Robust
Soft-Start
Low Shutdown Current: <2μA
Internally Compensated
Internal Boost Diode
Thermally Enhanced 2mm
×
2mm 8-Lead DFN
APPLICATIONS
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Automotive Systems
Battery-Powered Equipment
Wall Transformer Regulation
Distributed Supply Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
90
V
IN
4.7V TO 40V
BD
V
IN
1μF
SW
LT3502A
DA
31.6k
OFF ON
SHDN
GND
FB
10k
10μF
BOOST
0.1μF 6.8μH
EFFICIENCY (%)
V
OUT
3.3V
500mA
80
5V
OUT
70
60
50
40
30
20
10
3502TA01a
LT3502A 12V
IN
Efficiency
3.3V
OUT
0
0
0.1
0.3
0.2
LOAD CURRENT (A)
0.4
0.5
3502 TA01b
3502f
1
LT3502/LT3502A
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
Input Voltage (V
IN
) ....................................................40V
BOOST Voltage .........................................................50V
BOOST Pin Above SW Pin...........................................7V
FB Voltage ...................................................................6V
⎯
S
⎯
H
⎯
D
⎯
N Voltage ...........................................................40V
BD Voltage ..................................................................7V
Operating Junction Temperature Range (Note 2)
LT3502AE, LT3502E ........................... –40°C to 125°C
LT3502AI, LT3502I ............................ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
TOP VIEW
V
IN
1
BD 2
FB 3
SHDN 4
9
8 SW
7 BOOST
6 DA
5 GND
DC PACKAGE
8-LEAD (2mm
×
2mm) PLASTIC DFN
θ
JA
= 102°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3502EDC
LT3502IDC
LT3502AEDC
LT3502AIDC
DC PART MARKING*
LCLV
LCLV
LCLT
LCLT
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.
*The temperature grade is identified by a label on the shipping container.
ELECTRICAL CHARACTERISTICS
PARAMETER
Undervoltage Lockout
Quiescent Current at Shutdown
Quiescent Current
Feedback Voltage
Reference Voltage Line Regulation
FB Pin Bias Current
Switching Frequency
(Note 5)
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 10V, V
⎯
S
⎯
H
⎯
D
⎯
N
= 5V, V
BOOST
= 15V.
CONDITIONS
V
⎯
S
⎯
H
⎯
D
⎯
N
= 0V
Not Switching
●
MIN
2.6
TYP
2.8
0.5
1.5
MAX
3
2
2
0.813
0.81
50
2.7
2.8
1.3
1.4
UNITS
V
μA
mA
V
V
%/V
nA
MHz
MHz
MHz
MHz
%
%
mV
0.785
0.79
0.8
0.8
0.005
15
●
●
●
I
DA
< 500mA (LT3502A)
I
DA
< 500mA (LT3502A)
I
DA
< 500mA (LT3502)
I
DA
< 500mA (LT3502)
100mA Load (LT3502A)
100mA Load (LT3502)
I
SW
= 500mA
(Note 3)
SW = 10V (Note 4)
SW = 0V (Note 5)
I
SW
= 500mA
I
SW
= 500mA
I
OUT
= 100mA
1.9
1.8
0.9
0.8
70
80
0.75
2.25
2.25
1.1
1.1
80
90
450
0.9
95
8
10
1.9
0.8
Maximum Duty Cycle
Switch V
CESAT
Switch Current Limit
Switch Active Current
BOOST Pin Current
Minimum BOOST Voltage Above Switch
BOOST Schottky Forward Drop
DA Pin Current to Stop OSC
1.1
130
30
13
2.2
1
A
μA
μA
mA
V
V
mA
3502f
500
650
2
LT3502/LT3502A
ELECTRICAL CHARACTERISTICS
PARAMETER
⎯
S
⎯
H
⎯
D
⎯
N Bias Current
⎯
S
⎯
H
⎯
D
⎯
N Input Voltage High
⎯
S
⎯
H
⎯
D
⎯
N Input Voltage Low
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 LT3502EDC and LT3502AEDC are guaranteed to meet
performance specifications from 0°C to 125°C junction temperature
range. Specifications over the –40°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 10V, V
⎯
S
⎯
H
⎯
D
⎯
N
= 5V, V
BOOST
= 15V.
CONDITIONS
V
⎯
S
⎯
H
⎯
D
⎯
N
= 5V
V
⎯
S
⎯
H
⎯
D
⎯
N
= 0V
2
0.3
MIN
TYP
55
MAX
80
1
UNITS
μA
μA
V
V
with statistical process controls. The LT3502IDC and LT3502AIDC are
guaranteed over the – 40°C to 125°C operating junction temperature
range.
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 into pin.
Note 5:
Current flows out of pin.
TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A 3.3V
OUT
Efficiency
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0
0.1
0.3
0.2
LOAD CURRENT (A)
0.4
0.5
3502 G01
(T
A
= 25°C unless otherwise noted)
LT3502 3.3V
OUT
Efficiency
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
24V
IN
12V
IN
5V
IN
LT3502A 5V
OUT
Efficiency
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0
0.1
0.3
0.2
LOAD CURRENT (A)
0.4
0.5
3502 G02
12V
IN
12V
IN
24V
IN
24V
IN
0
0
0.1
0.3
0.4
0.2
LOAD CURRENT (A)
0.5
3502 G03
LT3502 5V
OUT
Efficiency
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
0.1
0.3
0.4
0.2
LOAD CURRENT (A)
0.5
3502 G04
LT3502A Maximum Load Current
V
OUT
= 3.3V, L = 6.8μH
1.0
1.0
TYPICAL
LOAD CURRENT (A)
MINIMUM
0.9
0.9
0.8
LOAD CURRENT (A)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
10
20
V
IN
(V)
30
40
3502 G05
LT3502A Maximum Load Current
V
OUT
= 5V, L = 10μH
TYPICAL
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
10
20
V
IN
(V)
30
40
3502 G06
12V
IN
24V
IN
MINIMUM
3502f
3
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS
LT3502 Maximum Load Current
V
OUT
= 3.3V, L = 15μH
0.9
0.8
0.7
LOAD CURRENT (A)
0.6
0.5
0.4
0.3
0.2
0.1
0
0
10
20
V
IN
(V)
3502 G07
(T
A
= 25°C unless otherwise noted)
LT3502 Maximum Load Current
V
OUT
= 5V, L = 22μH
0.9
700
TYPICAL
0.7
LOAD CURRENT (A)
0.6
0.5
0.4
0.3
200
0.2
0.1
100
0
0
10
20
V
IN
(V)
3502 G08
Switch Voltage Drop
600
500
V
CE
(mV)
400
300
25°C
125°C
TYPICAL
MINIMUM
0.8
MINIMUM
–40°C
30
40
0
30
40
0
0.2
0.4
0.6
0.8
1.0
3502 G09
SWITCH CURRENT (A)
UVLO
3.5
3.0
FREQUENCY (MHz)
2.5
V
IN
(V)
2.0
1.5
1.0
0.5
0
–50
2.5
Switching Frequency
0.9
LT3502A
SWITCH CURRENT LIMIT (A)
2.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
100
TEMPERATURE (°C)
50
150
3502 G10
Soft-Start (
⎯
S
⎯
H
⎯
D
⎯
N)
1.5
LT3502
1.0
0.5
0
–50
–0.1
0
100
TEMPERATURE (°C)
50
150
3502 G11
0
200 400 600 800 1000 1200 1400 1600
SHDN PIN VOLTAGE (mV)
3502 G12
⎯
S
⎯
H
⎯
D
⎯
N Pin Current
300
250
SHDN PIN CURRENT (μA)
CURRENT LIMIT (A)
200
150
100
50
0
0
5
10 15 20 25 30 35
SHDN PIN VOLTAGE (V)
40
45
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Switch Current Limit
1.2
1.0
CURRENT LIMIT (A)
Switch Current Limit
SW PEAK CURRENT LIMIT
DA VALLEY CURRENT LIMIT
LT3502
0.8
0.6
0.4
0.2
0
0
50
DUTY CYCLE (%)
100
3502 G18
LT3502A
0
–50
0
50
100
TEMPERATURE (°C)
150
3502 G14
3502 G13
3502f
4
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A Maximum V
IN
for Full
Frequency (V
OUT
= 3.3V)
45
40
35
30
V
IN
(V)
25
20
15
10
5
0
0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
T
A
= 85°C
V
IN
(V)
T
A
= 25°C
45
40
35
30
T
A
= 85°C
V
IN
(V)
25
20
15
10
5
0
0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
T
A
= 25°C
(T
A
= 25°C unless otherwise noted)
LT3502 Maximum V
IN
for Full
Frequency (V
OUT
= 3.3V)
45
40
35
30
25
20
15
10
5
0
0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
T
A
= 25°C
T
A
= 85°C
LT3502A Maximum V
IN
for Full
Frequency (V
OUT
= 5V)
3502 G15
3502 G16
3502 G17
LT3502A Typical Minimum Input
Voltage (V
OUT
= 3.3V)
7
6
5
V
IN
(V)
V
IN
(V)
4
3
2
1
0
0.001
8
7
6
5
4
3
2
1
0.1
0.01
LOAD CURRENT (A)
1
3502 G19
LT3502A Typical Minimum Input
Voltage (V
OUT
= 5V)
7
6
5
V
IN
(V)
4
3
2
1
LT3502 Typical Minimum Input
Voltage (V
OUT
= 3.3V)
0
0.001
0.01
0.1
LOAD CURRENT (A)
1
3502 G20
0
0.001
0.1
0.01
LOAD CURRENT (A)
1
3502 G21
LT3502 Typical Minimum Input
Voltage (V
OUT
= 5V)
8
7
6
5
V
IN
(V)
4
3
2
1
0
0.001
0.01
0.1
LOAD CURRENT (A)
1
3502 G22
Continuous Mode Waveform
V
SW
5V/DIV
V
SW
5V/DIV
Discontinuous Mode Waveform
I
L
200mA/DIV
V
OUT
20mV/DIV
V
IN
= 12V
V
OUT
= 3.3V
L = 6.8μH
C
OUT
= 10μF
I
OUT
= 250mA
200ns/DIV
3502 G23
I
L
200mA/DIV
V
OUT
20mV/DIV
V
IN
= 12V
V
OUT
= 3.3V
L = 6.8μH
C
OUT
= 10μF
I
OUT
= 30mA
200ns/DIV
3502 G24
3502f
5
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