LINER LTDTS

LT3502/LT3502A
1.1MHz/2.2MHz, 500mA
Step-Down Regulators in
2mm × 2mm DFN and MS10
DESCRIPTION
FEATURES
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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.
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
during start-up. DA current sense provides further protection in fault conditions. An internal boost diode reduces
component count.
APPLICATIONS
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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
5VOUT
BOOST
VIN
1μF
0.1μF 6.8μH
SW
LT3502A
VOUT
3.3V
500mA
DA
OFF ON
31.6k
SHDN
FB
GND
3.3VOUT
70
10k
10μF
EFFICIENCY (%)
VIN
4.7V TO 40V
60
50
40
30
20
10
3502 TA01a
0
0
0.1
0.3
0.2
LOAD CURRENT (A)
0.4
0.5
3502 TA01b
3502fc
1
LT3502/LT3502A
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage (VIN) ....................................................40V
BOOST Voltage .........................................................50V
BOOST Pin Above SW Pin...........................................7V
FB Voltage ...................................................................6V
SHDN 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
PIN CONFIGURATION
TOP VIEW
BD 2
TOP VIEW
8 SW
VIN 1
9
FB 3
SHDN 4
SW
BOOST
NC
DA
GND
7 BOOST
6 DA
5 GND
10
9
8
7
6
1
2
3
4
5
VIN
NC
BD
FB
SHDN
MS PACKAGE
10-LEAD PLASTIC MSOP
DC PACKAGE
8-LEAD (2mm × 2mm) PLASTIC DFN
θJA = 110°C/W
θJA = 102°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
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.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
Undervoltage Lockout
Quiescent Current at Shutdown
MIN
TYP
MAX
2.6
2.8
3
V
0.5
2
μA
1.5
2
mA
0.8
0.8
0.8
0.8
0.813
0.81
0.816
0.813
VSHDN = 0V
Quiescent Current
Not Switching
Feedback Voltage
2mm × 2mm DFN
2mm × 2mm DFN
MS10
MS10
●
●
0.785
0.79
0.780
0.786
Reference Voltage Line Regulation
0.005
FB Pin Bias Current
(Note 5)
Switching Frequency
IDA < 500mA (LT3502A)
IDA < 500mA (LT3502A)
IDA < 500mA (LT3502)
IDA < 500mA (LT3502)
●
●
●
UNITS
V
V
V
V
%/V
15
50
nA
1.9
1.8
0.9
0.8
2.25
2.25
1.1
1.1
2.7
2.8
1.3
1.4
MHz
MHz
MHz
MHz
70
80
80
90
%
%
450
mV
Maximum Duty Cycle
100mA Load (LT3502A)
100mA Load (LT3502)
Switch VCESAT
ISW = 500mA
Switch Current Limit
(Note 3)
0.9
1.1
A
Switch Active Current
SW = 10V (Note 4)
SW = 0V (Note 5)
95
8
130
30
μA
μA
BOOST Pin Current
ISW = 500mA
10
13
mA
Minimum BOOST Voltage Above Switch
ISW = 500mA
1.9
2.2
V
BOOST Schottky Forward Drop
IOUT = 100mA
0.8
1
V
DA Pin Current to Stop OSC
SHDN Bias Current
0.75
500
VSHDN = 5V
VSHDN = 0V
SHDN Input Voltage High
SHDN 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
650
55
mA
80
1
2
μA
μA
V
0.3
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.
3502fc
3
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A 3.3VOUT Efficiency
LT3502A 5VOUT Efficiency
12VIN
70
12VIN
70
24VIN
EFFICIENCY (%)
60
50
40
30
24VIN
80
60
50
40
30
40
30
20
10
10
0
0
0.3
0.2
LOAD CURRENT (A)
0
0.5
0.4
0.1
0.3
0.2
LOAD CURRENT (A)
12VIN
1.0
1.0
0.9
0.9
TYPICAL
50
40
30
TYPICAL
MINIMUM
0.7
0.6
0.5
0.4
0.3
0.7
0.5
0.4
0.3
20
0.2
10
0.1
0.1
0
0
0.1
0.3
0.4
0.2
LOAD CURRENT (A)
0.5
0
0
10
20
VIN (V)
30
3502 G04
40
TYPICAL
600
MINIMUM
500
0.7
0.5
0.4
0.3
0.6
0.5
0.4
0.3
0.2
0.2
0.1
0.1
30
40
VIN (V)
VCE (mV)
LOAD CURRENT (A)
MINIMUM
0.6
20
30
700
0.8
TYPICAL
0.7
10
20
VIN (V)
Switch Voltage Drop
0.9
0
10
3502 G06
LT3502 Maximum Load Current
VOUT = 5V, L = 22μH
0.9
0
0
40
3502 G05
LT3502 Maximum Load Current
VOUT = 3.3V, L = 15μH
0.8
MINIMUM
0.6
0.2
0
0.5
0.8
LOAD CURRENT (A)
LOAD CURRENT (A)
60
0.3
0.4
0.2
LOAD CURRENT (A)
LT3502A Maximum Load Current
VOUT = 5V, L = 10μH
0.8
24VIN
70
0.1
3502 G03
LT3502A Maximum Load Current
VOUT = 3.3V, L = 6.8μH
100
80
0
3502 G02
LT3502 5VOUT Efficiency
90
0.5
0.4
3502 G01
EFFICIENCY (%)
50
10
0.1
12VIN
60
20
0
24VIN
70
20
0
5VIN
90
80
EFFICIENCY (%)
80
EFFICIENCY (%)
LT3502 3.3VOUT Efficiency
100
90
90
LOAD CURRENT (A)
(TA = 25°C unless otherwise noted)
0
125°C
300
200
100
0
0
10
20
30
40
0
0.2
0.4
0.6
0.8
1.0
SWITCH CURRENT (A)
VIN (V)
3502 G07
–40°C
25°C
400
3502 G08
3502 G09
3502fc
4
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS
UVLO
(TA = 25°C unless otherwise noted)
Switching Frequency
3.5
Soft-Start (SHDN)
0.9
2.5
LT3502A
0.8
3.0
FREQUENCY (MHz)
VIN (V)
2.5
2.0
1.5
1.0
SWITCH CURRENT LIMIT (A)
2.0
1.5
LT3502
1.0
0.5
0.5
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
–50
0
50
0
–50
150
100
TEMPERATURE (°C)
–0.1
0
50
100
TEMPERATURE (°C)
3502 G10
0
150
200 400 600 800 1000 1200 1400 1600
SHDN PIN VOLTAGE (mV)
3502 G12
3502 G11
SHDN Pin Current
Switch Current Limit
Switch Current Limit
1.0
300
1.2
0.9
0.8
200
150
100
1.0
SW PEAK CURRENT LIMIT
0.7
CURRENT LIMIT (A)
CURRENT LIMIT (A)
SHDN PIN CURRENT (μA)
250
DA VALLEY CURRENT LIMIT
0.6
0.5
0.4
0.3
0.2
50
LT3502
0.8
LT3502A
0.6
0.4
0.2
0.1
0
0
5
10
15 20 25 30 35
SHDN PIN VOLTAGE (V)
40
0
–50
45
0
0
LT3502A Maximum VIN for Full
Frequency (VOUT = 3.3V)
LT3502 Maximum VIN for Full
Frequency (VOUT = 3.3V)
45
TA = 25°C
35
TA = 85°C
45
40
40
35
35
30
VIN (V)
25
20
30
TA = 25°C
25
VIN (V)
30
TA = 85°C
20
15
15
10
10
5
5
5
0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
3502 G16
TA = 85°C
20
15
0
TA = 25°C
25
10
0
100
3502 G15
LT3502A Maximum VIN for Full
Frequency (VOUT = 5V)
45
40
50
DUTY CYCLE (%)
3502 G14
3502 G13
VIN (V)
0
150
50
100
TEMPERATURE (°C)
0
0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
3502 G17
0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
3502 G18
3502fc
5
LT3502/LT3502A
TYPICAL PERFORMANCE CHARACTERISTICS
LT3502A Typical Minimum Input
Voltage (VOUT = 3.3V)
(TA = 25°C unless otherwise noted)
LT3502A Typical Minimum Input
Voltage (VOUT = 5V)
LT3502 Typical Minimum Input
Voltage (VOUT = 3.3V)
7
8
7
6
7
6
6
5
5
3
VIN (V)
4
VIN (V)
VIN (V)
5
4
4
3
3
2
2
2
1
1
1
0
0.001
0.1
0.01
LOAD CURRENT (A)
1
0
0.001
0.01
0.1
LOAD CURRENT (A)
1
0
0.001
0.1
0.01
LOAD CURRENT (A)
3502 G20
3502 G19
LT3502 Typical Minimum Input
Voltage (VOUT = 5V)
1
3502 G21
Continuous Mode Waveform
Discontinuous Mode Waveform
8
7
5
VIN (V)
VSW
5V/DIV
VSW
5V/DIV
6
IL
200mA/DIV
4
3
IL
200mA/DIV
VOUT
20mV/DIV
VOUT
20mV/DIV
2
1
0
0.001
0.01
0.1
LOAD CURRENT (A)
1
VIN = 12V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
IOUT = 250mA
200ns/DIV
3502 G23
VIN = 12V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
IOUT = 30mA
200ns/DIV
3502 G24
3502 G22
3502fc
6
LT3502/LT3502A
PIN FUNCTIONS
(DFN/MS)
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 divider tap to this pin. Set the output voltage according to
VOUT = 0.8(1 + R1/R2). A good value for R2 is 10k.
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 VIN pin. The SHDN pin also provides soft-start and
frequency foldback. To use the soft-start feature, connect
R3 and C4 to the SHDN pin. SHDN Pin voltage should
not be higher than VIN.
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.
3502fc
7
8
ON OFF
VIN
C4
R3
C2
4
1
SHDN
VIN
SLOPE
COMP
FREQUENCY
FOLDBACK
OSC
INT REG
AND
UVLO
∑
VC
gm
S
R
R2
0.8V
Q
Q
3
R1
FB
DRIVER
Q1
GND
DA
SW
BOOST
BD
5
6
8
7
2
C1
L1
D1
C3
3502 BD
VOUT
LT3502/LT3502A
BLOCK DIAGRAM
3502fc
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
between the VIN and SW pins, turning the switch off when
this current reaches a level determined by the voltage at
VC. An error amplifier measures the output voltage through
an external resistor divider tied to the FB pin and servos
the VC node. If the error amplifier’s output increases, more
current is delivered to the output; if it decreases, less
current is delivered. An active clamp (not shown) on the VC
node provides current limit. The VC node is also clamped
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 circuitry. This regulator includes an undervoltage lockout to
prevent switching when VIN 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.
The switch driver operates from either VIN or from the
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.
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 voltage. The DA comparator works in conjunction with the
switch peak current limit comparator to determine the
maximum deliverable current of the LT3502/LT3502A. The
peak current limit comparator is used in normal current
mode operations and is used to turn off the switch. The DA
valley current comparator monitors the catch diode current
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.
3502fc
9
LT3502/LT3502A
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resistors according to:
V
R1= R2 OUT – 1
0.8V R2 should be 20k or less to avoid bias current errors.
Reference designators refer to the Block Diagram.
Input Voltage Range
The input voltage range for the LT3502/LT3502A applications depends on the output voltage and on the absolute
maximum ratings of the VIN and BOOST pins.
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:
VOUT + VD
DC =
VIN – VSW + VD
where VD is the forward voltage drop of the catch diode
(~0.4V) and VSW is the voltage drop of the internal switch
(~0.45V at maximum load). This leads to a minimum input
voltage of:
V +V
VIN(MIN) = OUT D – VD + VSW
DCMAX
with DCMAX = 0.80 for the LT3502A and 0.90 for the
LT3502.
The maximum input voltage is determined by the
absolute maximum ratings of the VIN and BOOST pins. For
fixed frequency operation, the maximum input voltage is
determined by the minimum duty cycle DCMIN:
V +V
VIN(MAX) = OUT D – VD + VSW
DCMIN
Note that this is a restriction on the operating input voltage for fixed frequency operation; the circuit will tolerate
transient inputs up to the absolute maximum ratings of
the VIN and BOOST pins. The input voltage should be
limited to the VIN operating range (40V) during overload
conditions.
Minimum On Time
The LT3502/LT3502A will still regulate the output at input
voltages that exceed VIN(MAX) (up to 40V), however, the
output voltage ripple increases as the input voltage is
increased.
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).
When the required on time decreases below the minimum
on time of 60ns, instead of the switch pulse width becoming
narrower to accommodate the lower duty cycle requirement, the switch pulse width remains fixed at 60ns. The
inductor current ramps up to a value exceeding the load current and the output ripple increases. The part then remains
VSW
20V/DIV
IL
500mA/DIV
VOUT
100mV/DIV
VIN = 33V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
IOUT = 250mA
1μs/DIV
3502 F01
Figure 1. Continuous Mode Operation Near
Minimum On Time of 60ns
DCMIN = 0.15 for the LT3502A and 0.08 for the LT3502.
3502fc
10
LT3502/LT3502A
APPLICATIONS INFORMATION
VSW
20V/DIV
VSW
20V/DIV
IL
500mA/DIV
IL
500mA/DIV
VOUT
100mV/DIV
VOUT
100mV/DIV
VIN = 40V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
IOUT = 250mA
1μs/DIV
3502 F02
Figure 2. Pulse Skip Occurs when
Required On Time is Below 60ns
off until the output voltage dips below the programmed
value before it begins switching again (Figure 2).
Provided that the load can tolerate the increased output
voltage ripple and that the components have been properly
selected, operation above VIN(MAX) is safe and will not
damage the part.
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
VIN(MAX) the only component requirement is that the
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:
VIN – VOUT
• 60ns
L
The part is robust enough to survive prolonged operation
under these conditions as long as the peak inductor current does not exceed 1.2A. Inductor current saturation
and junction temperature may further limit performance
during this operating regime.
900mA +
VIN = 40V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
IOUT = 500mA
1μs/DIV
3502 F03
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
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is:
L = 1.6(VOUT + VD) for the LT3502A
L = 4.6(VOUT + VD) for the LT3502
where VD is the voltage drop of the catch diode (~0.4V) and
L is in μH. With this value there will be no subharmonic
oscillation for applications with 50% or greater duty cycle.
The inductor’s RMS current rating must be greater than the
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.
To keep efficiency high, the series resistance (DCR) should
be less than 0.1Ω. Table 1 lists several vendors and types
that are suitable.
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 operation, 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.
3502fc
11
LT3502/LT3502A
APPLICATIONS INFORMATION
Table 1
VENDOR
Sumida
URL
www.sumida.com
Toko
www.toko.com
Würth Elektronik
www.we-online.com
PART SERIES
CDRH4D28
CDRH5D28
CDRH8D28
A916CY
D585LC
WE-TPC(M)
WE-PD2(M)
WE-PD(S)
Catch Diode
A low capacitance 500mA Schottky diode is recommended
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.
Input Capacitor
Bypass the input of the LT3502/LT3502A circuit with a 1μF
or higher value ceramic capacitor of X7R or X5R type. Y5V
types have poor performance over temperature and applied
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.
Step-down regulators draw current from the input supply
in pulses with very fast rise and fall times. The input capacitor 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.
A 1μF capacitor is capable of this task, but only if it is placed
close to the LT3502/LT3502A and the catch diode (see the
PCB Layout section). A second precaution regarding the
ceramic input capacitor concerns the maximum input voltage rating of the LT3502/LT3502A. A ceramic input capacitor combined with trace or cable inductance forms a high
INDUCTANCE RATE (μH)
1.2 to 4.7
2.5 to 10
2.5 to 33
2 to 12
1.1 to 39
1 to 10
2.2 to 22
1 to 27
SIZE (mm)
4.5 × 4.5
5.5 × 5.5
8.3 × 8.3
6.3 × 6.2
8.1 × 8
4.8 × 4.8
5.2 × 5.8
7.3 × 7.3
quality (underdamped) tank circuit. If the LT3502/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.
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
switching frequency is important. The second function is to
store energy in order to satisfy transient loads and stabilize
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:
COUT =
33
for the LT3502A
VOUT
COUT =
66
for the LT3502
VOUT
where COUT is in μF. Use an X5R or X7R type and keep
in mind that a ceramic capacitor biased with VOUT will
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:
25
COUT =
VOUT
where COUT is in μF. However, using an output capacitor
this small results in an increased loop crossover frequency
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
0.1Ω or less. Such a capacitor will be larger than a ceramic
capacitor and will have a larger capacitance, because the
capacitor must be large to achieve low ESR. Table 2 lists
several capacitor vendors.
Figure 4 shows the transient response of the LT3502A with
several output capacitor choices. The output is 3.3V. The
load current is stepped from 150mA to 400mA and back to
150mA, and the oscilloscope traces show the output voltage.
The upper photo shows the recommended value. The second photo shows the improved response (less voltage drop)
resulting from a larger output capacitor and a phase lead
capacitor. The last photo shows the response to a high
performance electrolytic capacitor. Transient performance
is improved due to the large output capacitance.
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 0.1μF 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
BAT54) in parallel with the internal diode to reduce VD. The
following equations can be used to calculate and minimize
boost capacitance in μF:
0.012/(VBD + VCATCH – VD – 2.2) for the LT3502A
0.030/(VBD + VCATCH – VD– 2.2) for the LT3502
VD is the forward drop of the boost diode, and VCATCH is
the forward drop of the catch diode (D1).
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
www.panasonic.com
Kemet
(864) 963-6300
www.kemet.com
Sanyo
(408)794-9714
www.sanyovideo.com
Murata
AVX
(404) 436-1300
www.murata.com
www.avxcorp.com
Taiyo Yuden
(864) 963-6300
www.taiyo-yuden.com
PART SERIES
Ceramic
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
COMMENTS
EEF Series
T494,T495
POSCAP
TPS Series
3502fc
13
LT3502/LT3502A
APPLICATIONS INFORMATION
VOUT
32.4k
FB
IL
0.2A/DIV
10μF
VOUT
0.1V/DIV
AC COUPLED
10k
10μs/DIV
3502 F04a
10μs/DIV
3502 F04b
10μs/DIV
3502 F04c
VOUT
32.4k
50pF
IL
0.2A/DIV
10μF
×2
FB
VOUT
0.1V/DIV
AC COUPLED
10k
VOUT
32.4k
+
FB
10k
IL
0.2A/DIV
100μF
VOUT
0.1V/DIV
AC COUPLED
SANYO
4TPB100M
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
VDD
BD
BD
BOOST
VIN
VIN LT3502 SW
GND
BOOST
VOUT
VIN
DA
VBOOST – VSW ≅ VOUT
MAX VBOOST ≅ VIN + VOUT
VIN LT3502 SW
GND
DA
VBOOST – VSW ≅ VIN
MAX VBOOST ≅ 2VIN
3502 F05a
(5a)
VOUT
3502 F05b
(5b)
Figure 5
3502fc
14
LT3502/LT3502A
APPLICATIONS INFORMATION
The minimum operating voltage of an LT3502/LT3502A
application is limited by the undervoltage lockout (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 VIN
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
approximately 400mV above VOUT. At higher load currents,
the inductor current is continuous and the duty cycle is
limited by the maximum duty cycle of the LT3502/LT3502A,
requiring a higher input voltage to maintain regulation.
7
8
6
7
6
5
4
3
RUN
5
VIN (V)
VIN (V)
START
START
RUN
4
3
2
2
1
0
0.001
1
0.1
0.01
LOAD CURRENT (A)
0
0.001
1
0.01
0.1
LOAD CURRENT (A)
3502 G20
3502 G19
(6a) LT3502A Typical Minimum Input Voltage, VOUT = 3.3V
(6b) LT3502A Typical Minimum Input Voltage, VOUT = 5V
7
8
6
7
6
RUN
START
3
4
3
2
2
1
1
0
0.001
START
RUN
5
VIN (V)
VIN (V)
5
4
1
0.1
0.01
LOAD CURRENT (A)
0
0.001
1
0.01
0.1
LOAD CURRENT (A)
1
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
VSW
10V/DIV
RUN
SHDN
GND
IL
500mA/DIV
3502 F07a
VOUT
2V/DIV
VIN = 12V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
5μs/DIV
VIN = 12V
VOUT = 3.3V
L = 6.8μH
COUT = 10μF
50μs/DIV
RUN
VSW
10V/DIV
50k
SHDN
0.1μF
GND
IL
500mA/DIV
3502 F07b
VOUT
2V/DIV
3502 F07
Figure 7. To Soft Start the LT3502A, Add a Resistor and Capacitor to the SHDN Pin
Soft-Start
The SHDN pin can be used to soft start the LT3502/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.
Short and Reverse Protection
If the inductor is chosen so that it won’t saturate excessively,
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
battery charging applications or in battery backup systems
where a battery or some other supply is diode OR-ed with
the LT3502/LT3502A’s output. If the VIN pin is allowed to
float and the SHDN pin is held high (either by a logic signal
or because it is tied to VIN), then the LT3502/LT3502A’s
VSW
10V/DIV
IL
500mA/DIV
VIN = 40V
VOUT = 0V
L = 6.8μH
COUT = 10μF
2μs/DIV
3502 F08a
Figure 8a. The LT3502A Reduces its Frequency to Below 500kHz
to Protect Against Shorted Output with 40V Input
3502fc
16
LT3502/LT3502A
APPLICATIONS INFORMATION
D4
VIN
BD
BOOST
VIN
VOUT
SW
LT3502A
DA
SHDN
+
FB
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
VIN pin is grounded while the output is held high, then
parasitic diodes inside the LT3502/LT3502A can pull large
currents from the output through the SW pin and the VIN
pin. Figure 8b shows a circuit that will run only when the
input voltage is present and that protects against a shorted
or reversed input.
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,
these capacitors can cause problems if the LT3502/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
circuit, and the voltage at the VIN pin of the LT3502/LT3502A
can ring to twice the nominal input voltage, possibly exceeding 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
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
ripple filtering and can slightly improve the efficiency of the
circuit, though it is likely to be the largest component in the
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.
Frequency Compensation
The LT3502/LT3502A use current mode control to regulate
the output. This simplifies loop compensation. In particular,
the LT3502/LT3502A does not require the ESR of the output
capacitor for stability allowing the use of ceramic capacitors
to achieve low output ripple and small circuit size.
Figure 10 shows an equivalent circuit for the LT3502/
LT3502A control loop. The error amp is a transconductance
amplifier with finite output impedance. The power section,
consisting of the modulator, power switch and inductor,
is modeled as a transconductance amplifier generating an
output current proportional to the voltage at the VC node.
Note that the output capacitor integrates this current,
and that the capacitor on the VC node (CC) integrates the
error amplifier output current, resulting in two poles in the
loop. RC provides a zero. With the recommended output
capacitor, the loop crossover occurs above the RCCC zero.
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
ceramic capacitor (very low ESR), crossover may be lower
and a phase lead capacitor (CPL) across the feedback
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
IIN
VIN
DANGER!
LT3502
VIN
20V/DIV
+
RINGING VIN MAY EXCEED
ABSOLUTE MAXIMUM
RATING OF THE LT3502
2.2μF
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
IIN
5A/DIV
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
20μs/DIV
(9a)
VIN
20V/DIV
LT3502
+
10μF
35V
AI.EI.
+
2.2μF
IIN
5A/DIV
(9b)
20μs/DIV
1Ω
VIN
20V/DIV
LT3502
+
0.1μF
2.2μF
IIN
5A/DIV
(9c)
20μs/DIV
3502 F09
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
SW
gm =
+1A/V
LT3502
–
0.5V
OUT
R1
–
gm =
100μA/V
RC
150k
CC
70pF
GND
ERROR
AMPLIFIER
+
VC
CPL
FB
ESR
800mV
C1
+
C1
1M
R2
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 operating 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.
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 VIN and SW pins,
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
SW and BOOST nodes. Include vias near the exposed GND
pad of the LT3502/LT3502A to help remove heat from the
LT3502/LT3502A to the ground plane.
VOUT
C1
L1
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 calculating 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.
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
sum of input and output voltages cannot exceed the BOOST
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.
C2
VIN
C3
BST
R1
BD
FB
SHDN
10V
BD
VIN
20V TO 40V
VIN
BOOST
C3
0.1μF
C2
1μF
D1
DA
L1
33μH
SW
LT3502A
VOUT
15V
500mA
22pF
DA
R2
R1
180k
GND
OFF ON
3502 F11
= VIA
SHDN
FB
GND
3502 F12
Figure 11
R2
10k
C1
10μF
Figure 12. 15V Step-Down Converter
3502fc
19
LT3502/LT3502A
TYPICAL APPLICATIONS
0.8V Step-Down Converter
VBD
3V TO 7V
VBD
3V TO 7V
0.1μF
BD
VIN
3V TO 40V
C2
1μF
VIN
BOOST
L1
C3
0.1μF 3.3μH
SW
LT3502A
D1
0.1μF
BD
VIN
3V TO 40V
C2
1μF
VOUT
0.8V
500mA
VIN
BOOST
C3
0.1μF
SW
LT3502
DA
OFF ON
SHDN
L1
10μH
D1
VOUT
0.8V
500mA
DA
FB
OFF ON
SHDN
C1
47μF
GND
C1: JMK212BJ476MG
C3: HMK212BJ104MG
L1: LQH43CN3R3M03
FB
C1
100μF
GND
C1: JMK316BJ107ML
L1: LQH43CN100K03
3502 TA02a
3502 TA02b
1.8V Step-Down Converter
VBD
3V TO 7V
VBD
3V TO 7V
0.1μF
0.1μF
BD
VIN
3V TO 40V
C2
1μF
VIN
BOOST
L1
C3
0.1μF 4.7μH
SW
LT3502A
D1
DA
OFF ON
SHDN
C2
1μF
VOUT
1.8V
500mA
VIN
BOOST
C3
0.1μF
SW
LT3502
D1
DA
R1
12.5k
FB
GND
BD
VIN
3V TO 40V
OFF ON
R2
10k
C1: JMK212BJ226MG
L1: LQH43CN4R7M03
C1
22μF
3502 TA03a
SHDN
L1
15μH
VOUT
1.8V
500mA
R1
12.5k
FB
GND
R2
10k
C1: JMK212BJ476MG
L1: LQH55DN150M03
C1
47μF
3502 TA03b
3502fc
20
LT3502/LT3502A
TYPICAL APPLICATIONS
2.5V Step-Down Converter
VBD
3V TO 7V
VBD
3V TO 7V
0.1μF
BD
VIN
3.5V TO 40V
C2
1μF
VIN
BOOST
L1
C3
0.1μF 6.8μH
SW
LT3502A
D1
DA
OFF ON
SHDN
BD
VIN
3.5V TO 40V
C2
1μF
VOUT
2.5V
500mA
VIN
BOOST
C3
0.1μF
LT3502
D1
DA
R1
21.3k
SHDN
OFF ON
R2
10k
C1: JMK212BJ226MG
L1: LQH43DN6R8M03
L1
15μH
SW
FB
GND
0.1μF
C1
22μF
VOUT
2.5V
500mA
R1
21.3k
FB
R2
10k
GND
C1
22μF
C1: JMK212BJ226MG
L1: LQH55DN150M03
3502 TA04a
3502 TA04b
3.3V Step-Down Converter
BD
VIN
4.7V TO 40V
VIN
BOOST
C2
1μF
SW
LT3502A
D1
DA
OFF ON
L1
C3
0.1μF 6.8μH
SHDN
VIN
BOOST
C3
0.1μF
C2
1μF
VOUT
3.3V
500mA
SW
LT3502
D1
DA
R1
31.6k
FB
GND
BD
VIN
4.5V TO 40V
OFF ON
R2
10k
C1: LMK316BJ106ML-BR
L1: LQH43CN6R8M03
C1
10μF
3502 TA05a
SHDN
L1
15μH
VOUT
3.3V
500mA
R1
31.6k
FB
GND
R2
10k
C1: JMK212BJ226MG
L1: LQH55DN150M03
C1
22μF
3502 TA05b
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
1.15 ±0.05 0.64 ±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 = 0.05
TYP
2.00 ±0.10
(4 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
R = 0.115
TYP
5
8
0.40 ± 0.10
0.64 ± 0.10
(2 SIDES)
PIN 1 NOTCH
R = 0.20 OR
0.25 × 45°
CHAMFER
(DC8) DFN 0106 REVØ
4
0.200 REF
1
0.23 ± 0.05
0.45 BSC
0.75 ±0.05
1.37 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
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)
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
10 9 8 7 6
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0.497 ± 0.076
(.0196 ± .003)
REF
0° – 6° TYP
GAUGE PLANE
1 2 3 4 5
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 ± 0.0508
(.004 ± .002)
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 representation 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
VIN
6.7V TO 40V
VIN
BOOST
C3
0.1μF
C2
1μF
SW
LT3502A
D1
DA
OFF ON
L1
10μH
SHDN
VIN
BOOST
C3
0.1μF
C2
1μF
VOUT
5V
500mA
LT3502
R1
52.3k
R2
10k
C1
10μF
C1: LMK316BJ106ML-BR
L1: LQH43CN100K03
OFF ON
L1
22μH
SW
D1
DA
FB
GND
BD
VIN
6.4V TO 40V
SHDN
R1
52.3k
FB
GND
R2
10k
C1: LMK316BJ106ML-BR
L1: LQH43CN100K03
3502 TA06a
VOUT
5V
500mA
C1
22μF
3502 TA06b
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1766
60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down
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VIN: 5.5V to 60V, VOUT(MIN) = 1.2V, IQ = 2.5mA, ISD = 25μA,
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500mA (IOUT), 500kHz, Step-Down Switching Regulator in
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LT1936
36V, 1.4A (IOUT), 500kHz, High Efficiency Step-Down
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MS8E Package
LT1940
Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.6V to 25V, VOUT(MIN) = 1.20V, IQ = 3.8mA, ISD < 30μA,
TSSOP16E Package
LT1976/LT1977
60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency StepDown DC/DC Converters with Burst Mode® Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA,
TSSOP16E Package
LTC 3407/LTC3407-2
Dual 600mA/800mA, 1.5MHz/2.25MHz, Synchronous
Step-DownDC/DC Converters
VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD <1μA,
3mm × 3mm DFN, MS10E Package
LT3434/LT3435
60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency StepDown DC/DC Converters with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA,
TSSOP16E Package
LT3437
60V, 400mA (IOUT), Micropower Step-Down DC/DC
Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100μA, ISD < 1μA,
DFN Package
LT3493
36V, 1.4A (IOUT), 750kHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1μA,
DFN Package
LT3501
Dual 25V, 3A (IOUT), 1.5MHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10μA,
TSSOP20E Package
LT3503
20V, 1A (IOUT), 2.2MHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.6V to 20V, VOUT(MIN) = 0.78V, IQ = 1.9mA, ISD < 1μA,
2mm × 3mm DFN Package
LT3505
36V, 1.2A (IOUT), 3MHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.6V to 36V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD < 2μA,
3mm × 3mm DFN, MS8E Packages
LT3506/LT3506A
Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz, High Efficiency
Step-Down DC/DC Converters
VIN: 3.6V to 25V, VOUT(MIN) = 0.8V, IQ = 3.8mA, ISD < 30μA,
4mm × 5mm DFN Package
LT3508
Dual 36V, 1.4A (IOUT), 2.5MHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 4.3mA, ISD < 1μA,
4mm × 4mm QFN, TSSOP16E Packages
LT3510
Dual 25V, 2A (IOUT), 1.5MHz, High Efficiency Step-Down
DC/DC Converter
VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10μA,
TSSOP20E Package
LTC3548
Dual 400mA + 800mA, 2.25MHz Synchronous Step-Down
DC/DC Converter
VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA,
3mm × 3mm DFN, MS10E Packages
Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
3502fc
24 Linear Technology Corporation
LT 0908 REV C • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007