LT3502/LT3502A
1.1MHz/2.2MHz, 500mA
Step-Down Regulators in
Features
n
3V to 40V Input Voltage Range
n
500mA Output Current
n
Switching Frequency: 2.2MHz (LT3502A),
1.1MHz (LT3502)
n
800mV Feedback Voltage
n
Short-Circuit Robust
n
Soft-Start
n
Low Shutdown Current: <2µA
n
Internally Compensated
n
Internal Boost Diode
n
Thermally Enhanced 2mm × 2mm 8-Lead DFN
and 10-Lead MS10 Package
applications
n
Automotive Systems
n
Battery-Powered Equipment
n
Wall Transformer Regulation
n
Distributed Supply Regulation
2mm ×
2mm DFN and MS10
Description
The LT®3502/LT3502A are current mode PWM step-down
DC/DC converters with an internal 500mA power switch,
in tiny 8-lead 2mm × 2mm DFN and 10-lead MS10
packages. 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
provide protection against shorted outputs. Soft-start
and frequency foldback eliminates input current surge
during start-up. DA current sense provides further protec
tion in fault conditions. An internal boost diode reduces
component count.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
-
typical application
3.3V Step-Down Converter
V
4.7V TO 40V
IN
1µF
OFF ON
V
IN
SHDN
BD
BOOST
SW
LT3502A
DA
FB
GND
10k
0.1µF
6.8µH
31.6k
V
OUT
3.3V
500mA
10µF
3502 TA01a
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0
LT3502A 12VIN Efficiency
5V
OUT
0.1 0.3
0.2
LOAD CURRENT (A)
3.3V
OUT
0.4
0.5
3502 TA01b
3502fd
1
LT3502/LT3502A
TOP VIEW
absolute MaxiMuM ratings
Input Voltage (VIN) ....................................................40V
BOOST Voltage .........................................................50V
BOOST Pin Above SW Pin ...........................................7V
FB Voltage ...................................................................6V
SHDN Voltage ...........................................................40V
pin conFiguration
TOP VIEW
1
V
IN
2
BD
3
FB
SHDN
4
8-LEAD (2mm × 2mm) PLASTIC DFN
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
DC PACKAGE
= 102°C/W
θ
JA
8
SW
BOOST
7
9
DA
6
GND
5
(Note 1)
BD Voltage ..................................................................7V
Operating Junction Temperature Range (Note 2)
LT3502AE, LT 3502E .......................... –40°C to 125°C
LT3502AI, LT3502I ............................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
10
1
SW
2
BOOST
3
NC
4
DA
5
GND
MS PACKAGE
10-LEAD PLASTIC MSOP
θ
= 110°C/W
JA
V
IN
NC
9
BD
8
FB
7
SHDN
6
orDer inForMation
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3502EDC#PBF LT3502EDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C
LT3502IDC#PBF LT3502IDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C
LT3502AEDC#PBF LT3502AEDC#TRPBF LCLT 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C
LT3502AIDC#PBF LT3502AIDC#TRPBF LCLT 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C
LT3502EMS#PBF LT3502EMS#TRPBF LTDTR 10-Lead Plastic MSOP –40°C to 125°C
LT3502IMS#PBF LT3502IMS#TRPBF LTDTR 10-Lead Plastic MSOP –40°C to 125°C
LT3502AEMS#PBF LT3502AEMS#TRPBF LTDTS 10-Lead Plastic MSOP –40°C to 125°C
LT3502AIMS#PBF LT3502AIMS#TRPBF LTDTS 10-Lead Plastic MSOP –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
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
.linear.com/leadfree/
2
3502fd
LT3502/LT3502A
electrical characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, V
PARAMETER CONDITIONS MIN TYP MAX UNITS
Undervoltage Lockout 2.6 2.8 3 V
Quiescent Current at Shutdown V
Quiescent Current Not Switching 1.5 2 mA
Feedback Voltage 2mm × 2mm DFN
Reference Voltage Line Regulation 0.005 %/V
FB Pin Bias Current (Note 5)
Switching Frequency I
Maximum Duty Cycle 100mA Load (LT3502A)
Switch V
Switch Current Limit (Note 3) 0.75 0.9 1.1 A
Switch Active Current SW = 10V (Note 4)
BOOST Pin Current I
Minimum BOOST Voltage Above Switch I
BOOST Schottky Forward Drop I
DA Pin Current to Stop OSC 500 650 mA
SHDN Bias Current V
SHDN Input Voltage High 2 V
SHDN Input Voltage Low 0.3 V
CESAT
= 0V 0.5 2 µA
SHDN
2mm × 2mm DFN
MS10
MS10
< 500mA (LT3502A)
DA
I
< 500mA (LT3502A)
DA
I
< 500mA (LT3502)
DA
I
< 500mA (LT3502)
DA
100mA Load (L
ISW = 500mA 450 mV
SW = 0V (Note 5)
= 500mA 10 13 mA
SW
= 500mA 1.9 2.2 V
SW
= 100mA 0.8 1 V
OUT
= 5V
SHDN
V
= 0V
SHDN
T3502)
SHDN
= 5V, V
BOOST
= 15V.
l
l
l
l
l
0.785
0.79
0.780
0.786
1.9
1.8
0.9
0.8
70
80
0.8
0.8
0.8
0.8
15 50 nA
2.25
2.25
1.1
1.1
80
90
95
55 80
0.813
0.81
0.816
0.813
2.7
2.8
1.3
1.4
8
130
30
1
MHz
MHz
MHz
MHz
µA
µA
µA
µA
V
V
V
V
%
%
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
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.
3502fd
3
LT3502/LT3502A
V
(mV)
LOAD CURRENT (A)
LOAD CURRENT (A)
EFFICIENCY (%)
LOAD CURRENT (A)
3502 G05
LOAD CURRENT (A)
3502 G06
EFFICIENCY (%)
0.5
0.5
90
3502 G02
typical perForMance characteristics
LT3502A 3.3V
90
80
70
60
50
40
30
20
10
0
0
LT3502 5V
100
90
80
70
60
50
40
30
20
10
0
0
0.1 0.3
0.1
Efficiency LT3502A 5V
OUT
12V
IN
24V
IN
EFFICIENCY (%)
0.3
0.4
0.4
0.5
3502 G04
0.2
LOAD CURRENT (A)
Efficiency
OUT
12V
IN
24V
IN
0.2
LOAD CURRENT (A)
Efficiency LT3502 3.3V
OUT
80
70
60
50
40
30
20
10
0
0
12V
0.1 0.3
0.2
LOAD CURRENT (A)
24V
IN
IN
LT3502A Maximum Load Current
V
= 3.3V, L = 6.8µH
OUT
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
TYPICAL
10
MINIMUM
20
VIN (V)
30
(TA = 25°C unless otherwise noted)
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.1
0.4
0
LOAD CURRENT (A)
LT3502A Maximum Load Current
V
= 5V, L = 10µH
OUT
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
40
0
10
Efficiency
OUT
5V
IN
12V
0.2
TYPICAL
MINIMUM
20
VIN (V)
24V
IN
IN
0.3
0.4
0.5
3502 G03
30
40
4
LT3502 Maximum Load Current
V
= 3.3V, L = 15µH
OUT
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
TYPICAL
MINIMUM
10
20
VIN (V)
30
3502 G07
LT3502 Maximum Load Current
V
= 5V, L = 22µH Switch Voltage Drop
OUT
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
40
0
0
TYPICAL
MINIMUM
10
20
VIN (V)
30
40
3502 G08
700
600
500
400
CE
300
200
100
0
0
–40°C
25°C
125°C
0.2 0.4 0.6 1.0
SWITCH CURRENT (A)
0.8
3502 G09
3502fd
LT3502/LT3502A
3502 G12
1600
3502 G13
3502 G14
150
45
0.7
V
(V)
45
45
typical perForMance characteristics
UVLO
3.5
3.0
2.5
2.0
(V)
IN
V
1.5
1.0
0.5
0
–50
SHDN Pin Current
300
250
200
150
100
SHDN PIN CURRENT (µA)
50
0
5 15
0
0 50 150
TEMPERATURE (°C)
10
20
SHDN PIN VOLTAGE (V)
100
3502 G10
35
25 45
40
30
Switching Frequency Soft-Start (SHDN)
2.5
2.0
1.5
1.0
FREQUENCY (MHz)
0.5
0
–50
LT3502A
LT3502
0
50
TEMPERATURE (°C)
100
Switch Current Limit
1.0
0.9
0.8
0.7
0.6
0.5
0.4
CURRENT LIMIT (A)
0.3
0.2
0.1
0
–50
SW PEAK CURRENT LIMIT
DA VALLEY CURRENT LIMIT
0
50
TEMPERATURE (°C)
100
(TA = 25°C unless otherwise noted)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
SWITCH CURRENT LIMIT (A)
0.1
0
–0.1
3502 G11
150
0
200 600
400
SHDN PIN VOLTAGE (mV)
800
Switch Current Limit
1.2
1.0
0.8
0.6
0.4
CURRENT LIMIT (A)
0.2
0
0
50 100
DUTY CYCLE (%)
1000
LT3502
LT3502A
1200
1400
3502 G15
LT3502A Maximum V
Frequency (V
40
35
30
25
(V)
IN
20
V
15
10
5
0
0
0.1
OUT
TA = 25°C
TA = 85°C
0.2
0.3
LOAD CURRENT (A)
for Full
IN
= 3.3V)
0.4
0.5 0.6
3502 G16
LT3502A Maximum VIN for Full
Frequency (V
40
35
30
25
IN
20
15
10
5
0
0
TA = 25°C
TA = 85°C
0.2
0.1
= 5V)
OUT
0.3 0.7
LOAD CURRENT (A)
0.4
0.5 0.6
3502 G17
LT3502 Maximum VIN for Full
Frequency (V
40
35
30
25
(V)
IN
20
V
15
10
5
0
0
TA = 25°C
TA = 85°C
0.1
0.2
= 3.3V)
OUT
0.3 0.7
LOAD CURRENT (A)
0.4
0.5 0.6
3502 G18
3502fd
5
LT3502/LT3502A
OUT
OUT
typical perForMance characteristics
LT3502A Typical Minimum Input
(V)
IN
V
7
6
5
4
3
2
1
0
0.001
Voltage (V
= 3.3V)
OUT
0.01
LOAD CURRENT (A)
LT3502 Typical Minimum Input
(V)
IN
V
8
7
6
5
4
3
2
1
0
0.001
Voltage (V
= 5V)
OUT
0.01 0.1 1
LOAD CURRENT (A)
0.1 1
3502 G19
200mA/DIV
20mV/DIV
3502 G22
LT3502A Typical Minimum Input
(V)
IN
V
8
7
6
5
4
3
2
1
0
0.001
Voltage (V
= 5V)
OUT
0.01 0.1 1
LOAD CURRENT (A)
Continuous Mode Waveform Discontinuous Mode Waveform
V
SW
5V/DIV
I
L
V
OUT
VIN = 12V
= 3.3V
V
OUT
L = 6.8µH
= 10µF
C
OUT
= 250mA
I
200ns/DIV
(TA = 25°C unless otherwise noted)
LT3502 Typical Minimum Input
3502 G20
3502 G23
(V)
IN
V
V
5V/DIV
200mA/DIV
V
OUT
20mV/DIV
Voltage (V
7
6
5
4
3
2
1
0
0.001
SW
I
L
VIN = 12V
V
OUT
L = 6.8µH
C
OUT
I
= 3.3V
= 10µF
= 30mA
= 3.3V)
OUT
0.01
LOAD CURRENT (A)
200ns/DIV
0.1 1
3502 G21
3502 G24
3502fd
6
LT3502/LT3502A
pin Functions
VIN (Pin 1/Pin 10): The VIN pin supplies current to the
LT3502/LT3502A’s internal regulator and to the internal
power switch. This pin must be locally bypassed.
BD (Pin 2/Pin 8): The BD pin is used to provide current
to the internal boost Schottky diode.
FB (Pin 3/Pin 7): The LT3502/LT3502A regulate their
feedback pin to 0.8V. Connect the feedback resistor di
vider tap to this pin. Set the output voltage according to
= 0.8 (1 + R1/R2). A good value for R2 is 10k.
V
OUT
SHDN (Pin 4/Pin 6): The SHDN pin is used to put the
LT3502 in shutdown mode. Tie to ground to shut down
the LT3502/LT3502A. Tie to 2V or more for normal
operation. If the shutdown feature is not used, tie this pin
pin. The SHDN pin also provides soft-start and
V
to the
frequency foldback. To use the soft-start feature, connect
R3 and C4 to the SHDN pin. SHDN Pin voltage should
not be higher than V
IN
IN
(DFN/MS)
-
.
GND (Pin 5/Pin 5): Ground Pin.
DA (Pin 6/Pin 4): Connect the catch diode (D1) anode to
this pin. This pin is used to provide frequency foldback
in extreme situations.
BOOST (Pin 7/Pin 2): The BOOST pin is used to provide a
drive voltage, higher than the input voltage, to the internal
bipolar NPN power switch. Connect a boost capacitor from
this pin to SW Pin.
SW (Pin 8/Pin 1): The SW pin is the output of the internal
power switch. Connect this pin to the inductor, catch diode
and boost capacitor.
3502fd
7
LT3502/LT3502A
block DiagraM
BD
OUT
V
3502 BD
C1
L1
C3
7
2
BOOST
Q1
DRIVER
Q
Q
SW
D1
5
DA
6
GND
FB
3
R2 R1
0.8V
8
R
S
m
g
C
V
∑
COMP
SLOPE
AND
UVLO
INT REG
IN
V
1
C2
IN
V
SHDN
4
R3
ON OFF
OSC
FREQUENCY
FOLDBACK
C4
8
3502fd
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