LT3502AEDC [Linear]
IC 1.1 A SWITCHING REGULATOR, 2800 kHz SWITCHING FREQ-MAX, PDSO10, 2 X 2 MM, PLASTIC, DFN-10, Switching Regulator or Controller;
| 型号： | LT3502AEDC |
| 厂家： | 
Linear |
| 描述： | IC 1.1 A SWITCHING REGULATOR, 2800 kHz SWITCHING FREQ-MAX, PDSO10, 2 X 2 MM, PLASTIC, DFN-10, Switching Regulator or Controller 稳压器 |
| 文件： | 总24页 (文件大小：387K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3502/LT3502A
1.1MHz/2.2MHz, 500mA
Step-Down Regulators in
2mm × 2mm DFN and MS10
DESCRIPTION
FEATURES
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.Thewideinputvoltagerangeof3Vto40Vmakes
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
abovetheAMbandavoidsinterferingwithradioreception,
making the LT3502A particularly suitable for automotive
applications.
■
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
■
■
■
■
■
■
■
and 10-lead MS10 Package
Cycle-by-cycle current limit and frequency foldback
provide protection against shorted outputs. Soft-start
and frequency foldback eliminates input current surge
duringstart-up. DAcurrentsenseprovidesfurtherprotec-
tion in fault conditions. An internal boost diode reduces
component count.
APPLICATIONS
■
Automotive Systems
■
Battery-Powered Equipment
Wall Transformer Regulation
■
■
Distributed Supply Regulation
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
LT3502A 12VIN Efficiency
3.3V Step-Down Converter
90
80
BD
5V
3.3V
OUT
V
OUT
IN
V
BOOST
SW
IN
70
60
50
40
30
20
10
4.7V TO 40V
1μF
0.1μF
6.8μH
31.6k
V
OUT
3.3V
500mA
LT3502A
DA
FB
SHDN
OFF ON
GND
10k
10μF
3502 TA01a
0
0
0.4
0.5
0.1
0.2
0.3
LOAD CURRENT (A)
3502 TA01b
3502fc
1
LT3502/LT3502A
(Note 1)
ABSOLUTE MAXIMUM RATINGS
Input Voltage (V )....................................................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
IN
BOOST Voltage .........................................................50V
BOOST Pin Above SW Pin...........................................7V
FB Voltage...................................................................6V
SHDN Voltage ...........................................................40V
PIN CONFIGURATION
TOP VIEW
TOP VIEW
1
2
3
4
8
7
6
5
SW
V
IN
SW
BOOST
NC
1
2
3
4
5
10
9
V
IN
BD
FB
BOOST
DA
NC
9
8
BD
FB
SHDN
DA
7
6
SHDN
GND
GND
MS PACKAGE
10-LEAD PLASTIC MSOP
DC PACKAGE
8-LEAD (2mm × 2mm) PLASTIC DFN
θ
JA
= 110°C/W
θ
= 102°C/W
JA
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3502EDC#PBF
LT3502IDC#PBF
LT3502AEDC#PBF
LT3502AIDC#PBF
LT3502EMS#PBF
LT3502IMS#PBF
LT3502AEMS#PBF
LT3502AIMS#PBF
TAPE AND REEL
PART MARKING*
LCLV
PACKAGE DESCRIPTION
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
LT3502EDC#TRPBF
LT3502IDC#TRPBF
LT3502AEDC#TRPBF
LT3502AIDC#TRPBF
LT3502EMS#TRPBF
LT3502IMS#TRPBF
LT3502AEMS#TRPBF
LT3502AIMS#TRPBF
8-Lead 2mm × 2mm Plastic DFN
8-Lead 2mm × 2mm Plastic DFN
8-Lead 2mm × 2mm Plastic DFN
8-Lead 2mm × 2mm Plastic DFN
10-Lead Plastic MSOP
LCLV
LCLT
LCLT
LTDTR
LTDTR
LTDTS
LTDTS
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
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/
3502fc
2
LT3502/LT3502A
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VSHDN = 5V, VBOOST = 15V.
PARAMETER
CONDITIONS
MIN
TYP
2.8
0.5
1.5
MAX
UNITS
V
Undervoltage Lockout
Quiescent Current at Shutdown
Quiescent Current
2.6
3
2
2
V
SHDN
= 0V
μA
Not Switching
mA
●
●
Feedback Voltage
2mm × 2mm DFN
2mm × 2mm DFN
MS10
0.785
0.79
0.780
0.786
0.8
0.8
0.8
0.8
0.813
0.81
0.816
0.813
V
V
V
V
MS10
Reference Voltage Line Regulation
FB Pin Bias Current
0.005
15
%/V
nA
●
(Note 5)
50
Switching Frequency
I
I
I
I
< 500mA (LT3502A)
< 500mA (LT3502A)
< 500mA (LT3502)
< 500mA (LT3502)
1.9
1.8
0.9
0.8
2.25
2.25
1.1
2.7
2.8
1.3
1.4
MHz
MHz
MHz
MHz
DA
DA
DA
DA
●
●
1.1
Maximum Duty Cycle
100mA Load (LT3502A)
100mA Load (LT3502)
70
80
80
90
%
%
Switch V
I
= 500mA
SW
450
0.9
mV
A
CESAT
Switch Current Limit
Switch Active Current
(Note 3)
0.75
1.1
SW = 10V (Note 4)
SW = 0V (Note 5)
95
8
130
30
μA
μA
BOOST Pin Current
I
I
I
= 500mA
= 500mA
= 100mA
10
1.9
0.8
650
55
13
2.2
1
mA
V
SW
SW
OUT
Minimum BOOST Voltage Above Switch
BOOST Schottky Forward Drop
DA Pin Current to Stop OSC
SHDN Bias Current
V
500
2
mA
V
V
= 5V
= 0V
80
1
μA
μA
SHDN
SHDN
SHDN Input Voltage High
SHDN Input Voltage Low
V
V
0.3
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.
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.
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
Slope compensation reduces current limit at higher duty cycle.
Note 4: Current flows into pin.
Note 5: Current flows out of pin.
3502fc
3
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
LT3502A 3.3VOUT Efficiency
LT3502A 5VOUT Efficiency
LT3502 3.3VOUT Efficiency
100
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
12V
IN
5V
IN
24V
IN
12V
IN
24V
24V
IN
IN
12V
IN
0
0
0
0.1
0.2
0.3
0.4
0.5
0
0.4
0.5
40
40
0.1
0.2
0.3
0
0.4
0.5
0.1
0.2
0.3
LOAD CURRENT (A)
LOAD CURRENT (A)
LOAD CURRENT (A)
3502 G03
3502 G02
3502 G01
LT3502A Maximum Load Current
VOUT = 3.3V, L = 6.8μH
LT3502A Maximum Load Current
VOUT = 5V, L = 10μH
LT3502 5VOUT Efficiency
100
90
80
70
60
50
40
30
20
10
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
12V
IN
TYPICAL
TYPICAL
24V
IN
MINIMUM
MINIMUM
0
0.1
0.2
0.3
0.4
0.5
0
20
(V)
30
0
20
(V)
30
10
10
40
V
V
LOAD CURRENT (A)
IN
IN
3502 G04
3502 G05
3502 G06
LT3502 Maximum Load Current
VOUT = 3.3V, L = 15μH
LT3502 Maximum Load Current
OUT = 5V, L = 22μH
V
Switch Voltage Drop
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
700
600
TYPICAL
TYPICAL
MINIMUM
MINIMUM
500
400
300
200
100
0
–40°C
25°C
125°C
20
(V)
0
10
30
40
20
(V)
0
0.2
0.4
0.6
0.8
1.0
0
10
30
V
V
SWITCH CURRENT (A)
IN
IN
3502 G07
3502 G08
3502 G09
3502fc
4
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS
(TA = 25°C unless otherwise noted)
UVLO
Switching Frequency
Soft-Start (SHDN)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
3.5
3.0
2.5
2.5
2.0
1.5
1.0
0.5
0
LT3502A
2.0
1.5
1.0
0.5
0
LT3502
–0.1
0
50
150
1400
200 400 600 800 1000 1200 1600
–50
100
0
0
50
100
–50
150
SHDN PIN VOLTAGE (mV)
TEMPERATURE (°C)
TEMPERATURE (°C)
3502 G10
3502 G12
3502 G11
SHDN Pin Current
Switch Current Limit
Switch Current Limit
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
300
250
1.2
1.0
SW PEAK CURRENT LIMIT
DA VALLEY CURRENT LIMIT
LT3502
LT3502A
200
0.8
0.6
150
100
0.4
0.2
0
50
0
–50
0
50
100
150
0
5
10 15 20 25 30 35 40 45
0
50
DUTY CYCLE (%)
100
TEMPERATURE (°C)
SHDN PIN VOLTAGE (V)
3502 G14
3502 G13
3502 G15
LT3502A Maximum VIN for Full
Frequency (VOUT = 3.3V)
LT3502A Maximum VIN for Full
Frequency (VOUT = 5V)
LT3502 Maximum VIN for Full
Frequency (VOUT = 3.3V)
45
40
35
30
25
20
15
10
5
45
40
35
30
25
20
15
10
5
45
40
35
30
25
20
15
10
5
T
T
= 25°C
= 85°C
A
A
T
= 25°C
T = 25°C
A
A
T
= 85°C
T = 85°C
A
A
0
0
0
0
0.1 0.2 0.3
LOAD CURRENT (A)
0.7
0
0.1 0.2 0.3
LOAD CURRENT (A)
0.7
0
0.1 0.2 0.3
LOAD CURRENT (A)
0.7
0.4 0.5 0.6
0.4 0.5 0.6
0.4 0.5 0.6
3502 G16
3502 G17
3502 G18
3502fc
5
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
LT3502A Typical Minimum Input
Voltage (VOUT = 3.3V)
LT3502A Typical Minimum Input
Voltage (VOUT = 5V)
LT3502 Typical Minimum Input
Voltage (VOUT = 3.3V)
7
6
5
4
3
2
1
7
6
5
4
3
2
1
8
7
6
5
4
3
2
1
0
0
0
0.1
LOAD CURRENT (A)
1
0.1
LOAD CURRENT (A)
1
0.001
0.01
0.001
0.01
0.001
0.01
0.1
1
LOAD CURRENT (A)
3502 G20
3502 G21
3502 G19
LT3502 Typical Minimum Input
Voltage (VOUT = 5V)
Continuous Mode Waveform
Discontinuous Mode Waveform
8
7
6
5
4
3
2
1
0
V
V
SW
SW
5V/DIV
5V/DIV
I
L
200mA/DIV
I
L
200mA/DIV
V
OUT
V
OUT
20mV/DIV
20mV/DIV
3502 G23
3502 G24
V
V
= 12V
200ns/DIV
V
V
= 12V
200ns/DIV
IN
OUT
IN
OUT
= 3.3V
= 3.3V
L = 6.8μH
L = 6.8μH
C
= 10μF
C
= 10μF
OUT
OUT
OUT
OUT
0.001
0.01
0.1
1
I
= 250mA
I
= 30mA
LOAD CURRENT (A)
3502 G22
3502fc
6
LT3502/LT3502A
PIN FUNCTIONS (DFN/MS)
V
(Pin 1/Pin 10): The V pin supplies current to the
GND (Pin 5/Pin 5): Ground Pin.
IN
IN
LT3502/LT3502A’s internal regulator and to the internal
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.
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.
BOOST (Pin 7/Pin 2): The BOOST pin is used to provide a
drive voltage, higher than the input voltage, to the internal
bipolarNPNpowerswitch.Connectaboostcapacitorfrom
this pin to SW Pin.
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
V
OUT
= 0.8(1 + R1/R2). A good value for R2 is 10k.
SW (Pin 8/Pin 1): The SW pin is the output of the internal
powerswitch.Connectthispintotheinductor,catchdiode
and boost capacitor.
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
to the V pin. The SHDN pin also provides soft-start and
IN
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
3502fc
7
LT3502/LT3502A
BLOCK DIAGRAM
3502fc
8
LT3502/LT3502A
OPERATION
The LT3502/LT3502A are constant frequency, current
mode step-down regulators. An oscillator enables an RS
flip-flop, turning on the internal 500mA power switch Q1.
An amplifier and comparator monitor the current flowing
The switch driver operates from either V or from the
IN
BOOST pin. An external capacitor and the internal diode
are used to generate a voltage at the BOOST pin that is
higher than the input supply. This allows the driver to
fully saturate the internal bipolar NPN power switch for
efficient operation.
between the V and SW pins, turning the switch off when
IN
this current reaches a level determined by the voltage at
V .Anerroramplifiermeasurestheoutputvoltagethrough
C
A comparator monitors the current flowing through
the catch diode via the DA pin and reduces the LT3502/
LT3502A’s operating frequency when the DA pin current
exceeds the 650mA valley current limit. This frequency
foldback helps to control the output current in fault
conditions such as shorted output with high input volt-
age. The DA comparator works in conjunction with the
switch peak current limit comparator to determine the
maximumdeliverablecurrentoftheLT3502/LT3502A. The
peak current limit comparator is used in normal current
modeoperationsandisusedtoturnofftheswitch. TheDA
valleycurrentcomparatormonitorsthecatchdiodecurrent
and will delay switching until the catch diode current is
below the 650mA limit. Maximum deliverable current to
the output is therefore limited by both switch peak current
limit and DA valley current limit.
an external resistor divider tied to the FB pin and servos
the V node. If the error amplifier’s output increases, more
C
current is delivered to the output; if it decreases, less
currentisdelivered.Anactiveclamp(notshown)ontheV
C
node provides current limit. The V node is also clamped
C
to the voltage on the SHDN pin; soft-start is implemented
by generating a voltage ramp at the SHDN pin using an
external resistor and capacitor. The SHDN pin voltage
during soft-start also reduces the oscillator frequency to
avoid hitting current limit during start-up.
An internal regulator provides power to the control cir-
cuitry. This regulator includes an undervoltage lockout to
prevent switching when V is less than ~3V. The SHDN
pin is used to place the LT3502/LT3502A in shutdown,
disconnecting the output and reducing the input current
to less than 2μA.
IN
3502fc
9
LT3502/LT3502A
APPLICATIONS INFORMATION
FB Resistor Network
Note that this is a restriction on the operating input volt-
age for fixed frequency operation; the circuit will tolerate
transient inputs up to the absolute maximum ratings of
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
the V and BOOST pins. The input voltage should be
IN
limited to the V operating range (40V) during overload
IN
ꢀ
ꢃ
conditions.
VOUT
0.8V
R1= R2
– 1
ꢅ
ꢂ
ꢁ
ꢄ
Minimum On Time
R2 should be 20k or less to avoid bias current errors.
Reference designators refer to the Block Diagram.
The LT3502/LT3502A will still regulate the output at input
voltages that exceed V
(up to 40V), however, the
IN(MAX)
output voltage ripple increases as the input voltage is
Input Voltage Range
increased.
The input voltage range for the LT3502/LT3502A applica-
tions depends on the output voltage and on the absolute
As the input voltage is increased, the part is required to
switch for shorter periods of time. Delays associated with
turning off the power switch dictate the minimum on time
of the part. The minimum on time for the LT3502/LT3502A
is 60ns (Figure 1).
maximum ratings of the V and BOOST pins.
IN
The minimum input voltage is determined by either the
LT3502/LT3502A’s minimum operating voltage of 3V, or
by its maximum duty cycle. The duty cycle is the fraction
of time that the internal switch is on and is determined
by the input and output voltages:
When the required on time decreases below the minimum
ontimeof60ns,insteadoftheswitchpulsewidthbecoming
narrower to accommodate the lower duty cycle require-
ment, the switch pulse width remains fixed at 60ns. The
inductorcurrentrampsuptoavalueexceedingtheloadcur-
rentandtheoutputrippleincreases. Thepartthenremains
V
OUT + VD
DC =
V – VSW + VD
IN
where V is the forward voltage drop of the catch diode
D
(~0.4V) and V is the voltage drop of the internal switch
SW
(~0.45Vatmaximumload). Thisleadstoaminimuminput
V
voltage of:
SW
20V/DIV
V
OUT + VD
V
=
– VD + VSW
IN(MIN)
DCMAX
I
L
500mA/DIV
with DC
LT3502.
= 0.80 for the LT3502A and 0.90 for the
V
MAX
OUT
100mV/DIV
3502 F01
V
V
= 33V
1μs/DIV
IN
OUT
= 3.3V
The maximum input voltage is determined by the
L = 6.8μH
absolute maximum ratings of the V and BOOST pins. For
C
= 10μF
= 250mA
OUT
OUT
IN
I
fixed frequency operation, the maximum input voltage is
determined by the minimum duty cycle DC
:
MIN
Figure 1. Continuous Mode Operation Near
Minimum On Time of 60ns
V
OUT + VD
DCMIN
V
=
– VD + VSW
IN(MAX)
DC
= 0.15 for the LT3502A and 0.08 for the LT3502.
MIN
3502fc
10
LT3502/LT3502A
APPLICATIONS INFORMATION
V
SW
V
SW
20V/DIV
20V/DIV
I
L
I
L
500mA/DIV
500mA/DIV
V
V
OUT
OUT
100mV/DIV
100mV/DIV
3502 F02
3502 F03
V
V
= 40V
1μs/DIV
V
V
= 40V
1μs/DIV
IN
OUT
IN
OUT
= 3.3V
= 3.3V
L = 6.8μH
L = 6.8μH
C
= 10μF
= 250mA
C
= 10μF
= 500mA
OUT
OUT
OUT
OUT
I
I
Figure 2. Pulse Skip Occurs when
Required On Time is Below 60ns
Figure 3. Pulse Skip with Large Load Current Will be Limited
by the DA Valley Current Limit. Notice the Flat Inductor Valley
Current and Reduced Switching Frequency
off until the output voltage dips below the programmed
value before it begins switching again (Figure 2).
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is:
Provided that the load can tolerate the increased output
voltagerippleandthatthecomponentshavebeenproperly
L = 1.6(V
L = 4.6(V
+ V ) for the LT3502A
OUT
OUT
D
+ V ) for the LT3502
selected, operation above V
damage the part.
is safe and will not
D
IN(MAX)
whereV isthevoltagedropofthecatchdiode(~0.4V)and
D
L is in μH. With this value there will be no subharmonic
oscillationforapplicationswith50%orgreaterdutycycle.
Theinductor’sRMScurrentratingmustbegreaterthanthe
maximum load current and its saturation current should
be about 30% higher. For robust operation during fault
conditions, the saturation current should be above 1.2A.
Tokeepefficiencyhigh,theseriesresistance(DCR)should
be less than 0.1Ω. Table 1 lists several vendors and types
that are suitable.
As the input voltage increases, the inductor current ramps
up quicker, the number of skipped pulses increases and
the output voltage ripple increases. For operation above
V
the only component requirement is that the
IN(MAX)
components be adequately rated for operation at the
intended voltage levels.
Inductor current may reach current limit when operating
in pulse skip mode with small valued inductors. In this
case, the LT3502/LT3502A will periodically reduce its
frequency to keep the inductor valley current to 650mA
(Figure 3). Peak inductor current is therefore peak current
plus minimum switch delay:
There are several graphs in the Typical Performance
Characteristics section of this data sheet that show the
maximum load current as a function of input voltage and
inductor value for several popular output voltages. Low
inductance may result in discontinuous mode opera-
tion, which is okay, but further reduces maximum load
current. For details of the maximum output current and
discontinuous mode operation, see Linear Technology
Application Note 44.
V – VOUT
IN
900mA +
• 60ns
L
The part is robust enough to survive prolonged operation
under these conditions as long as the peak inductor cur-
rent does not exceed 1.2A. Inductor current saturation
and junction temperature may further limit performance
during this operating regime.
3502fc
11
LT3502/LT3502A
APPLICATIONS INFORMATION
Table 1
VENDOR
URL
PART SERIES
INDUCTANCE RATE (μH)
SIZE (mm)
Sumida
www.sumida.com
CDRH4D28
CDRH5D28
CDRH8D28
1.2 to 4.7
2.5 to 10
2.5 to 33
4.5 × 4.5
5.5 × 5.5
8.3 × 8.3
Toko
www.toko.com
A916CY
D585LC
2 to 12
1.1 to 39
6.3 × 6.2
8.1 × 8
Würth Elektronik
www.we-online.com
WE-TPC(M)
WE-PD2(M)
WE-PD(S)
1 to 10
2.2 to 22
1 to 27
4.8 × 4.8
5.2 × 5.8
7.3 × 7.3
Catch Diode
quality(underdamped)tankcircuit.IftheLT3502/LT3502A
circuit is plugged into a live supply, the input voltage can
ring to twice its nominal value, possibly exceeding the
LT3502/LT3502A’s voltage rating. This situation is easily
avoided; see the Hot Plugging Safely section.
Alowcapacitance500mASchottkydiodeisrecommended
for the catch diode, D1. The diode must have a reverse
voltage rating equal to or greater than the maximum input
voltage. The Phillips PMEG4005AEA is a good choice; it
is related for 500mA continuous forward current and a
maximum reverse voltage of 40V.
Output Capacitor
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated by
the LT3502/LT3502A to produce the DC output. In this role
it determines the output ripple so low impedance at the
switchingfrequencyisimportant.Thesecondfunctionisto
storeenergyinordertosatisfytransientloadsandstabilize
the LT3502/LT3502A’s control loop. Ceramic capacitors
have very low equivalent series resistance (ESR) and
provide the best ripple performance. A good value is:
Input Capacitor
Bypass the input of the LT3502/LT3502A circuit with a 1μF
or higher value ceramic capacitor of X7R or X5R type. Y5V
typeshavepoorperformanceovertemperatureandapplied
voltage and should not be used. A 1μF ceramic is adequate
to bypass the LT3502/LT3502A and will easily handle the
ripple current. However, if the input power source has
high impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
33
VOUT
COUT
=
for the LT3502A
for the LT3502
66
VOUT
Step-down regulators draw current from the input supply
in pulses with very fast rise and fall times. The input ca-
pacitor is required to reduce the resulting voltage ripple at
the LT3502/LT3502A and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A1μFcapacitoriscapableofthistask,butonlyifitisplaced
close to the LT3502/LT3502A and the catch diode (see the
PCB Layout section). A second precaution regarding the
ceramicinputcapacitorconcernsthemaximuminputvolt-
ageratingoftheLT3502/LT3502A. Aceramicinputcapaci-
tor combined with trace or cable inductance forms a high
COUT
=
where C
is in μF. Use an X5R or X7R type and keep
OUT
in mind that a ceramic capacitor biased with V
will
OUT
have less than its nominal capacitance. This choice will
provide low output ripple and good transient response.
Transient performance can be improved with a high value
capacitor, but a phase lead capacitor across the feedback
resistor, R1, may be required to get the full benefit (see
the Compensation section).
3502fc
12
LT3502/LT3502A
APPLICATIONS INFORMATION
For small size, the output capacitor can be chosen
according to:
BOOST Pin Considerations
Capacitor C3 and the internal boost diode are used to
generate a boost voltage that is higher than the input
voltage. In most cases a 0.1ꢀF capacitor will work well.
Figure 5 shows two ways to arrange the boost circuit. The
BOOST pin must be at least 2.2V above the SW pin for
best efficiency. For outputs of 3V and above, the standard
circuit (Figure 5a) is best. For outputs less than 3V and
above 2.5V, place a discrete Schottky diode (such as the
25
VOUT
COUT
=
where C
is in μF. However, using an output capacitor
OUT
thissmallresultsinanincreasedloopcrossoverfrequency
and increased sensitivity to noise.
High performance electrolytic capacitors can be used for
the output capacitor. Low ESR is important, so choose
one that is intended for use in switching regulators. The
ESR should be specified by the supplier and should be
0.1Ωorless. Suchacapacitorwillbelargerthanaceramic
capacitor and will have a larger capacitance, because the
capacitor must be large to achieve low ESR. Table 2 lists
several capacitor vendors.
BAT54)inparallelwiththeinternaldiodetoreduceV . The
D
following equations can be used to calculate and minimize
boost capacitance in ꢀF:
0.012/(V + V
– V – 2.2) for the LT3502A
D
BD
CATCH
0.030/(V + V
– V – 2.2) for the LT3502
D
BD
CATCH
V is the forward drop of the boost diode, and V
is
D
CATCH
the forward drop of the catch diode (D1).
Figure4showsthetransientresponseoftheLT3502Awith
several output capacitor choices. The output is 3.3V. The
loadcurrentissteppedfrom150mAto400mAandbackto
150mA,andtheoscilloscopetracesshowtheoutputvoltage.
The upper photo shows the recommended value. The sec-
ondphotoshowstheimprovedresponse(lessvoltagedrop)
resulting from a larger output capacitor and a phase lead
capacitor. The last photo shows the response to a high
performanceelectrolyticcapacitor.Transientperformance
is improved due to the large output capacitance.
For lower output voltages the BD pin can be tied to an
external voltage source with adequate local bypassing
(Figure 5b). The above equations still apply for calculating
the optimal boost capacitor for the chosen BD voltage.
The absence of BD voltage during startup will increase
minimum voltage to start and reduce efficiency. You must
also be sure that the maximum voltage rating of BOOST
pin is not exceeded.
Table 2
VENDOR
Panasonic
PHONE
(714) 373-7366
URL
PART SERIES
COMMENTS
EEF Series
T494,T495
www.panasonic.com
Ceramic
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic
Polymer,
Tantalum
Kemet
Sanyo
(864) 963-6300
(408)794-9714
www.kemet.com
www.sanyovideo.com
POSCAP
Murata
AVX
(404) 436-1300
(864) 963-6300
www.murata.com
www.avxcorp.com
Ceramic
Ceramic,
Tantalum
TPS Series
Taiyo Yuden
www.taiyo-yuden.com
Ceramic
3502fc
13
LT3502/LT3502A
APPLICATIONS INFORMATION
V
OUT
32.4k
FB
I
L
0.2A/DIV
10μF
V
OUT
10k
0.1V/DIV
AC COUPLED
3502 F04a
3502 F04b
3502 F04c
10μs/DIV
10μs/DIV
10μs/DIV
V
OUT
32.4k
FB
10k
50pF
I
L
10μF
×2
0.2A/DIV
V
OUT
0.1V/DIV
AC COUPLED
V
OUT
32.4k
FB
10k
+
I
L
100μF
0.2A/DIV
V
OUT
SANYO
4TPB100M
0.1V/DIV
AC COUPLED
Figure 4. Transient Load Response of the LT3502A with Different Output Capacitors
as the Load Current is Stepped from 150mA to 400mA. VIN = 12V, VOUT = 3.3V, L = 6.8μH
V
DD
BD
BD
BOOST
BOOST
V
LT3502
GND
V
OUT
V
SW
IN
IN
V
IN
LT3502
GND
V
OUT
V
SW
IN
DA
DA
V
– V ≅ V
SW OUT
BOOST
3502 F05a
BOOST
V
– V ≅ V
BOOST
3502 F05b
BOOST
SW
IN
IN
MAX V
≅ V + V
IN OUT
MAX V
≅ 2V
(5a)
(5b)
Figure 5
3502fc
14
LT3502/LT3502A
APPLICATIONS INFORMATION
The minimum operating voltage of an LT3502/LT3502A
applicationislimitedbytheundervoltagelockout(3V)and
by the maximum duty cycle as outlined above. For proper
start-up, the minimum input voltage is also limited by the
boost circuit. If the input voltage is ramped slowly, or the
LT3502/LT3502A is turned on with its SHDN pin when the
output is already in regulation, then the boost capacitor
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on the input and output voltages, and on the arrangement
of the boost circuit. The minimum load generally goes to
zero once the circuit has started. Figure 6 shows plots of
minimum load to start and to run as a function of input
voltage. In many cases the discharged output capacitor
will present a load to the switcher which will allow it to
start. The plots show the worst-case situation where V
IN
is ramping very slowly. At light loads, the inductor current
becomes discontinuous and the effective duty cycle can
be very high. This reduces the minimum input voltage to
approximately400mVaboveV .Athigherloadcurrents,
OUT
the inductor current is continuous and the duty cycle is
limitedbythemaximumdutycycleoftheLT3502/LT3502A,
requiring a higher input voltage to maintain regulation.
7
6
5
8
7
START
6
RUN
START
5
4
3
2
1
0
4
3
RUN
2
1
0
0.1
LOAD CURRENT (A)
1
0.001
0.01
0.001
0.01
0.1
1
LOAD CURRENT (A)
3502 G20
3502 G19
(6a) LT3502A Typical Minimum Input Voltage, VOUT = 3.3V
(6b) LT3502A Typical Minimum Input Voltage, VOUT = 5V
8
7
6
5
7
START
6
5
4
3
2
1
RUN
START
RUN
4
3
2
1
0
0
0.001
0.01
0.1
1
0.1
LOAD CURRENT (A)
1
0.001
0.01
LOAD CURRENT (A)
3502 G22
3502 G21
(6c) LT3502 Typical Minimum Input Voltage, VOUT = 3.3V
(6d) LT3502 Typical Minimum Input Voltage, VOUT = 5V
Figure 6
3502fc
15
LT3502/LT3502A
APPLICATIONS INFORMATION
V
SW
10V/DIV
RUN
SHDN
GND
I
L
500mA/DIV
3502 F07a
V
OUT
2V/DIV
5μs/DIV
V
V
= 12V
IN
OUT
= 3.3V
L = 6.8μH
= 10μF
C
OUT
RUN
50k
V
SW
10V/DIV
SHDN
GND
I
0.1μF
L
500mA/DIV
3502 F07b
V
OUT
2V/DIV
3502 F07
50μs/DIV
V
V
= 12V
IN
= 3.3V
OUT
L = 6.8μH
C
= 10μF
OUT
Figure 7. To Soft Start the LT3502A, Add a Resistor and Capacitor to the SHDN Pin
Soft-Start
batterychargingapplicationsorinbatterybackupsystems
where a battery or some other supply is diode OR-ed with
TheSHDNpincanbeusedtosoftstarttheLT3502/LT3502A,
reducing the maximum input current during start-up. The
SHDN pin is driven through an external RC filter to create
a voltage ramp at this pin. Figure 7 shows the start-up
waveforms with and without the soft-start circuit. By
choosing a large RC time constant, the peak start up
current can be reduced to the current that is required to
regulate the output, with no overshoot. Choose the value
of the resistor so that it can supply 80μA when the SHDN
pin reaches 2V.
the LT3502/LT3502A’s output. If the V pin is allowed to
IN
float and the SHDN pin is held high (either by a logic signal
or because it is tied to V ), then the LT3502/LT3502A’s
IN
V
SW
10V/DIV
Short and Reverse Protection
I
L
500mA/DIV
Iftheinductorischosensothatitwon’tsaturateexcessively,
the LT3502/LT3502A will tolerate a shorted output. When
operating in short-circuit condition, the LT3502/LT3502A
will reduce their frequency until the valley current is
650mA (Figure 8a). There is another situation to consider
in systems where the output will be held high when the
input to the LT3502/LT3502A is absent. This may occur in
3502 F08a
V
V
= 40V
2μs/DIV
IN
= 0V
OUT
L = 6.8μH
C
= 10μF
OUT
Figure 8a. The LT3502A Reduces its Frequency to Below 500kHz
to Protect Against Shorted Output with 40V Input
3502fc
16
LT3502/LT3502A
APPLICATIONS INFORMATION
input. The input voltage rings as high as 35V and the input
current peaks at 20A. One method of damping the tank
circuit is to add another capacitor with a series resistor to
the circuit. In Figure 9b an aluminum electrolytic capacitor
has been added. This capacitor’s high equivalent series
resistance damps the circuit and eliminates the voltage
overshoot. The extra capacitor improves low frequency
ripplefilteringandcanslightlyimprovetheefficiencyofthe
circuit,thoughitislikelytobethelargestcomponentinthe
circuit. An alternative solution is shown in Figure 9c. A 1Ω
resistor is added in series with the input to eliminate the
voltage overshoot (it also reduces the peak input current).
A 0.1μF capacitor improves high frequency filtering. This
solution is smaller and less expensive than the electrolytic
capacitor. For high input voltages its impact on efficiency
is minor, reducing efficiency less than one half percent for
a 5V output at full load operating from 24V.
D4
BD
V
V
BOOST
IN
IN
V
SW
OUT
LT3502A
DA
FB
+
SHDN
GND
3502 F08b
Figure 8b. Diode D4 Prevents a Shorted Input from Discharging
a Backup Battery Tied to the Output; it Also Protects the Circuit
from a Reversed Input. The LT3502/LT3502A Runs Only When
the Input is Present
internal circuitry will pull its quiescent current through
its SW pin. This is fine if your system can tolerate a few
mA in this state. If you ground the SHDN pin, the SW
pin current will drop to essentially zero. However, if the
Frequency Compensation
V
pin is grounded while the output is held high, then
IN
TheLT3502/LT3502Ausecurrentmodecontroltoregulate
theoutput.Thissimplifiesloopcompensation.Inparticular,
theLT3502/LT3502AdoesnotrequiretheESRoftheoutput
capacitorforstabilityallowingtheuseofceramiccapacitors
to achieve low output ripple and small circuit size.
parasitic diodes inside the LT3502/LT3502A can pull large
currents from the output through the SW pin and the V
IN
pin. Figure 8b shows a circuit that will run only when the
inputvoltageispresentandthatprotectsagainstashorted
or reversed input.
Figure 10 shows an equivalent circuit for the LT3502/
LT3502Acontrolloop.Theerrorampisatransconductance
amplifierwithfiniteoutputimpedance. Thepowersection,
consisting of the modulator, power switch and inductor,
is modeled as a transconductance amplifier generating an
Hot Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3502/LT3502A circuits. However,
thesecapacitorscancauseproblemsiftheLT3502/LT3502A
are plugged into a live supply (see Linear Technology
Application Note 88 for a complete discussion). The low
loss ceramic capacitor combined with stray inductance in
series with the power source forms an underdamped tank
output current proportional to the voltage at the V node.
C
Note that the output capacitor integrates this current,
and that the capacitor on the V node (C ) integrates the
C
C
error amplifier output current, resulting in two poles in the
loop. R provides a zero. With the recommended output
C
circuit,andthevoltageattheV pinoftheLT3502/LT3502A
capacitor, the loop crossover occurs above the R C zero.
IN
C C
can ring to twice the nominal input voltage, possibly ex-
ceeding the LT3502/LT3502A’s rating and damaging the
part. If the input supply is poorly controlled or the user
will be plugging the LT3502/LT3502A into an energized
supply, the input network should be designed to prevent
this overshoot. Figure 9 shows the waveforms that result
when an LT3502/LT3502A circuit is connected to a 24V
supply through six feet of 24-gauge twisted pair. The first
plot is the response with a 2.2μF ceramic capacitor at the
This simple model works well as long as the value of the
inductor is not too high and the loop crossover frequency
is much lower than the switching frequency. With a larger
ceramiccapacitor(verylowESR),crossovermaybelower
and a phase lead capacitor (C ) across the feedback
PL
divider may improve the phase margin and transient
response. Large electrolytic capacitors may have an ESR
large enough to create an additional zero, and the phase
lead may not be necessary.
3502fc
17
LT3502/LT3502A
APPLICATIONS INFORMATION
CLOSING SWITCH
SIMULATES HOT PLUG
I
IN
V
IN
DANGER!
LT3502
2.2μF
V
IN
20V/DIV
RINGING V MAY EXCEED
IN
ABSOLUTE MAXIMUM
RATING OF THE LT3502
+
I
IN
5A/DIV
LOW
STRAY
IMPEDANCE
ENERGIZED
24V SUPPLY
INDUCTANCE
20μs/DIV
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
(9a)
V
LT3502
2.2μF
IN
20V/DIV
+
+
+
10μF
35V
AI.EI.
I
IN
5A/DIV
(9b)
20μs/DIV
1Ω
V
LT3502
2.2μF
IN
20V/DIV
0.1μF
I
IN
5A/DIV
3502 F09
20μs/DIV
(9c)
Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation When the LT3502 is Connected to a Live Supply
CURRENT MODE
POWER STAGE
LT3502
–
0.5V
SW
g
=
m
OUT
1A/V
+
C
R1
PL
–
+
FB
g
=
V
C
m
100μA/V
ESR
800mV
R
C
C1
ERROR
AMPLIFIER
+
150k
C1
C
C
1M
70pF
R2
GND
3502 F10
Figure 10. Model for Loop Response
3502fc
18
LT3502/LT3502A
APPLICATIONS INFORMATION
If the output capacitor is different than the recommended
capacitor, stability should be checked across all operat-
ing conditions, including load current, input voltage and
temperature. The LT1375 data sheet contains a more
thorough discussion of loop compensation and describes
how to test the stability using a transient load.
High Temperature Considerations
The die temperature of the LT3502/LT3502A must be
lower than the maximum rating of 125°C. This is generally
not a concern unless the ambient temperature is above
85°C. For higher temperatures, care should be taken in
the layout of the circuit to ensure good heat sinking of
the LT3502/LT3502A. The maximum load current should
be derated as the ambient temperature approaches
125°C. The die temperature is calculated by multiplying
the LT3502/LT3502A power dissipation by the thermal
resistance from junction to ambient. Power dissipation
within the LT3502/LT3502A can be estimated by calculat-
ing the total power loss from an efficiency measurement
and subtracting the catch diode loss. Thermal resistance
depends on the layout of the circuit board, but 102°C/W
and 110ºC/W are typical for the (2mm × 2mm) DFN and
MS10 packages respectively.
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 11 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents flow in the LT3502/LT3502A’s V and SW pins,
IN
the catch diode (D1) and the input capacitor (C2). The
loop formed by these components should be as small
as possible and tied to system ground in only one place.
These components, along with the inductor and output
capacitor, should be placed on the same side of the circuit
board, and their connections should be made on that
layer. Place a local, unbroken ground plane below these
components, and tie this ground plane to system ground
at one location, ideally at the ground terminal of the output
capacitor C1. The SW and BOOST nodes should be as
small as possible. Finally, keep the FB node small so that
the ground pin and ground traces will shield it from the
SWandBOOSTnodes. IncludeviasneartheexposedGND
pad of the LT3502/LT3502A to help remove heat from the
LT3502/LT3502A to the ground plane.
Outputs Greater Than 7V
Note that for outputs above 7V, the input voltage range will
be limited by the maximum rating of the BOOST pin. The
sumofinputandoutputvoltagescannotexceedtheBOOST
pin’s 50V rating. The 15V circuit (Figure 12) shows how to
overcome this limitation using an additional zener diode.
Other Linear Technology Publications
Application notes AN19, AN35 and AN44 contain more
detailed descriptions and design information for Buck
regulators and other switching regulators. The LT1376
data sheet has a more extensive discussion of output
ripple, loop compensation and stability testing. Design
Note 100 shows how to generate a bipolar output supply
using a buck regulator.
V
OUT
C1
L1
C2
10V
BD
V
V
IN
IN
V
IN
BOOST
SW
C3
20V TO 40V
L1
33μH
C3
0.1μF
C2
1μF
V
D1
OUT
BST
DA
15V
500mA
FB
R1
LT3502A
BD
SHDN
22pF
DA
R2
R1
180k
GND
SHDN
FB
OFF ON
R2
10k
C1
10μF
3502 F11
GND
= VIA
3502 F12
Figure 11
Figure 12. 15V Step-Down Converter
3502fc
19
LT3502/LT3502A
TYPICAL APPLICATIONS
0.8V Step-Down Converter
V
BD
V
BD
3V TO 7V
3V TO 7V
0.1μF
0.1μF
BD
BD
V
V
IN
3V TO 40V
IN
V
BOOST
SW
V
BOOST
SW
IN
IN
3V TO 40V
L1
3.3μH
L1
10μH
C3
C3
C2
1μF
C2
1μF
V
V
OUT
0.1μF
0.1μF
OUT
0.8V
0.8V
500mA
500mA
LT3502A
LT3502
D1
D1
DA
FB
DA
FB
SHDN
SHDN
OFF ON
OFF ON
C1
47μF
C1
100μF
GND
GND
C1: JMK212BJ476MG
C3: HMK212BJ104MG
L1: LQH43CN3R3M03
C1: JMK316BJ107ML
L1: LQH43CN100K03
3502 TA02a
3502 TA02b
1.8V Step-Down Converter
V
V
BD
BD
3V TO 7V
3V TO 7V
0.1μF
0.1μF
BD
BD
V
V
IN
3V TO 40V
IN
V
BOOST
C3
V
BOOST
SW
IN
IN
3V TO 40V
L1
4.7μH
L1
15μH
C2
1μF
C2
1μF
C3
0.1μF
V
V
0.1μF
SW
OUT
OUT
1.8V
1.8V
500mA
500mA
LT3502A
LT3502
D1
D1
DA
FB
DA
FB
R1
R1
12.5k
12.5k
SHDN
SHDN
OFF ON
OFF ON
R2
10k
C1
22μF
R2
10k
C1
47μF
GND
GND
C1: JMK212BJ226MG
L1: LQH43CN4R7M03
C1: JMK212BJ476MG
L1: LQH55DN150M03
3502 TA03a
3502 TA03b
3502fc
20
LT3502/LT3502A
TYPICAL APPLICATIONS
2.5V Step-Down Converter
V
V
BD
BD
3V TO 7V
3V TO 7V
0.1μF
0.1μF
BD
BD
V
V
IN
IN
V
BOOST
V
BOOST
SW
IN
IN
3.5V TO 40V
3.5V TO 40V
L1
C3
L1
6.8μH
C2
1μF
C2
1μF
C3
15μH
V
V
0.1μF
0.1μF
OUT
2.5V
OUT
SW
DA
FB
2.5V
500mA
500mA
LT3502
LT3502A
D1
D1
DA
FB
R1
21.3k
R1
21.3k
SHDN
SHDN
OFF ON
OFF ON
R2
10k
C1
22μF
R2
10k
C1
22μF
GND
GND
C1: JMK212BJ226MG
L1: LQH55DN150M03
C1: JMK212BJ226MG
L1: LQH43DN6R8M03
3502 TA04b
3502 TA04a
3.3V Step-Down Converter
BD
BD
V
V
IN
IN
V
BOOST
SW
V
BOOST
SW
IN
IN
4.5V TO 40V
4.7V TO 40V
L1
15μH
L1
6.8μH
C3
0.1μF
C3
C2
1μF
C2
1μF
V
V
0.1μF
OUT
3.3V
OUT
3.3V
500mA
500mA
LT3502
LT3502A
D1
D1
DA
FB
DA
FB
R1
R1
31.6k
31.6k
SHDN
SHDN
OFF ON
OFF ON
R2
10k
C1
22μF
R2
10k
C1
10μF
GND
GND
C1: JMK212BJ226MG
L1: LQH55DN150M03
C1: LMK316BJ106ML-BR
L1: LQH43CN6R8M03
3502 TA05b
3502 TA05a
3502fc
21
LT3502/LT3502A
PACKAGE DESCRIPTION
DC Package
8-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1719 Rev Ø)
0.70 ±0.05
2.55 ±0.05
0.64 ±0.05
1.15 ±0.05
(2 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
0.45 BSC
1.37 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.115
TYP
5
8
R = 0.05
TYP
0.40 ± 0.10
PIN 1 NOTCH
2.00 ±0.10 0.64 ± 0.10
(4 SIDES)
(2 SIDES)
R = 0.20 OR
0.25 × 45°
CHAMFER
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
(DC8) DFN 0106 REVØ
4
1
0.23 ± 0.05
0.45 BSC
0.75 ±0.05
0.200 REF
1.37 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3502fc
22
LT3502/LT3502A
PACKAGE DESCRIPTION
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
0.889 0.127
(.035 .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
3.00 0.102
(.118 .004)
(NOTE 3)
(.0197)
0.497 0.076
(.0196 .003)
REF
0.50
0.305 0.038
(.0120 .0015)
TYP
10 9
8
7 6
BSC
RECOMMENDED SOLDER PAD LAYOUT
3.00 0.102
(.118 .004)
(NOTE 4)
4.90 0.152
(.193 .006)
DETAIL “A”
0° – 6° TYP
0.254
(.010)
GAUGE PLANE
1
2
3
4 5
0.53 0.152
(.021 .006)
0.86
(.034)
REF
1.10
(.043)
MAX
DETAIL “A”
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.1016 0.0508
(.004 .002)
0.50
(.0197)
BSC
MSOP (MS) 0307 REV E
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
3502fc
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LT3502/LT3502A
TYPICAL APPLICATION
5V Step-Down Converter
BD
BD
V
V
IN
IN
V
BOOST
SW
V
BOOST
SW
IN
IN
6.7V TO 40V
6.4V TO 40V
L1
10μH
C3
L1
22μH
C3
C2
1μF
C2
1μF
V
0.1μF
V
0.1μF
OUT
OUT
5V
5V
500mA
500mA
LT3502A
D1
LT3502
D1
DA
FB
DA
FB
R1
R1
52.3k
52.3k
SHDN
OFF ON
SHDN
OFF ON
R2
10k
C1
10μF
GND
R2
10k
C1
22μF
GND
C1: LMK316BJ106ML-BR
L1: LQH43CN100K03
C1: LMK316BJ106ML-BR
L1: LQH43CN100K03
3502 TA06a
3502 TA06b
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 5.5V to 60V, V
LT1766
60V, 1.2A (I ), 200kHz, High Efficiency Step-Down
DC/DC Converter
= 1.2V, I = 2.5mA, I = 25μA,
OUT(MIN) Q SD
OUT
IN
TSSOP16/TSSOP16E Packages
LT1933
500mA (I ), 500kHz, Step-Down Switching Regulator in V : 3.6V to 36V, V
= 1.2V, I = 1.6mA, I < 1μA,
OUT(MIN) Q SD
OUT
IN
SOT-23
ThinSOTTM Package
LT1936
36V, 1.4A (I ), 500kHz, High Efficiency Step-Down
V : 3.6V to 36V, V
= 1.2V, I = 1.9mA, I < 1μA,
Q SD
OUT
IN
OUT(MIN)
DC/DC Converter
MS8E Package
LT1940
Dual 25V, 1.4A (I ), 1.1MHz, High Efficiency Step-Down V : 3.6V to 25V, V
= 1.20V, I = 3.8mA, I < 30μA,
Q SD
OUT
IN
OUT(MIN)
DC/DC Converter
TSSOP16E Package
LT1976/LT1977
60V, 1.2A (I ), 200kHz/500kHz High Efficiency Step-
V : 3.3V to 60V, V
= 1.20V, I = 100μA, I < 1μA,
OUT(MIN) Q SD
OUT
IN
Down DC/DC Converters with Burst Mode® Operation
TSSOP16E Package
LTC 3407/LTC3407-2 Dual 600mA/800mA, 1.5MHz/2.25MHz, Synchronous
Step-DownDC/DC Converters
V : 2.5V to 5.5V, V
= 0.6V, I = 40μA, I <1μA,
Q SD
IN
OUT(MIN)
3mm × 3mm DFN, MS10E Package
LT3434/LT3435
60V, 1.2A (I ), 200kHz/500kHz High Efficiency Step-
V : 3.3V to 60V, V = 1.20V, I = 100μA, I < 1μA,
OUT
IN
OUT(MIN)
Q
SD
Down DC/DC Converters with Burst Mode Operation
TSSOP16E Package
LT3437
60V, 400mA (I ), Micropower Step-Down DC/DC
V : 3.3V to 60V, V
= 1.25V, I = 100μA, I < 1μA,
Q SD
OUT
IN
OUT(MIN)
OUT(MIN)
OUT(MIN)
Converter with Burst Mode Operation
DFN Package
LT3493
36V, 1.4A (I ), 750kHz, High Efficiency Step-Down
V : 3.6V to 36V, V
= 0.8V, I = 1.9mA, I < 1μA,
Q SD
OUT
IN
DC/DC Converter
DFN Package
LT3501
Dual 25V, 3A (I ), 1.5MHz, High Efficiency Step-Down
V : 3.3V to 25V, V
= 0.8V, I = 3.7mA, I < 10μA,
Q SD
OUT
IN
DC/DC Converter
TSSOP20E Package
LT3503
20V, 1A (I ), 2.2MHz, High Efficiency Step-Down
V : 3.6V to 20V, V
= 0.78V, I = 1.9mA, I < 1μA,
OUT(MIN) Q SD
OUT
IN
DC/DC Converter
2mm × 3mm DFN Package
V : 3.6V to 36V, V = 0.78V, I = 2mA, I < 2μA,
OUT(MIN) Q SD
LT3505
36V, 1.2A (I ), 3MHz, High Efficiency Step-Down
OUT
IN
DC/DC Converter
3mm × 3mm DFN, MS8E Packages
LT3506/LT3506A
LT3508
Dual 25V, 1.6A (I ), 575kHz/1.1MHz, High Efficiency
V : 3.6V to 25V, V = 0.8V, I = 3.8mA, I < 30μA,
OUT
IN
OUT(MIN)
Q
SD
Step-Down DC/DC Converters
4mm × 5mm DFN Package
Dual 36V, 1.4A (I ), 2.5MHz, High Efficiency Step-Down V : 3.6V to 36V, V
= 0.8V, I = 4.3mA, I < 1μA,
Q SD
OUT
IN
OUT(MIN)
DC/DC Converter
4mm × 4mm QFN, TSSOP16E Packages
LT3510
Dual 25V, 2A (I ), 1.5MHz, High Efficiency Step-Down
V : 3.3V to 25V, V = 0.8V, I = 3.7mA, I < 10μA,
OUT
IN
OUT(MIN)
Q
SD
DC/DC Converter
TSSOP20E Package
LTC3548
Dual 400mA + 800mA, 2.25MHz Synchronous Step-Down V : 2.5V to 5.5V, V
= 0.6V, I = 40μA, I < 1μA,
IN
OUT(MIN) Q SD
DC/DC Converter
3mm × 3mm DFN, MS10E Packages
Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
3502fc
LT 0908 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
24
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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