LT1613
1.4MHz, Single Cell DC/DC
Converter in 5-Lead SOT-23
FEATURES
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DESCRIPTIO
Uses Tiny Capacitors and Inductor
Internally Compensated
Fixed Frequency 1.4MHz Operation
Operates with V
IN
as Low as 1.1V
3V at 30mA from a Single Cell
5V at 200mA from 3.3V Input
15V at 60mA from Four Alkaline Cells
High Output Voltage: Up to 34V
Low Shutdown Current: <1µA
Low V
CESAT
Switch: 300mV at 300mA
Tiny 5-Lead SOT-23 Package
The LT
®
1613 is the industry’s first 5-lead SOT-23 current
mode DC/DC converter. Intended for small, low power
applications, it operates from an input voltage as low as
1.1V and switches at 1.4MHz, allowing the use of tiny, low
cost capacitors and inductors 2mm or less in height. Its
small size and high switching frequency enables the
complete DC/DC converter function to take up less than
0.2 square inches of PC board area. Multiple output power
supplies can now use a separate regulator for each output
voltage, replacing cumbersome quasi-regulated ap-
proaches using a single regulator and a custom trans-
former.
A constant frequency, internally compensated current
mode PWM architecture results in low, predictable output
noise that is easy to filter. The high voltage switch on the
LT1613 is rated at 36V, making the device ideal for boost
converters up to 34V as well as for Single-Ended Primary
Inductance Converter (SEPIC) and flyback designs. The
device can generate 5V at up to 200mA from a 3.3V supply
or 5V at 175mA from four alkaline cells in a SEPIC design.
The LT1613 is available in the 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Digital Cameras
Pagers
Cordless Phones
Battery Backup
LCD Bias
Medical Diagnostic Equipment
Local 5V or 12V Supply
External Modems
PC Cards
TYPICAL APPLICATIO
L1
4.7µH
V
IN
3.3V
D1
V
OUT
5V
200mA
100
95
90
EFFICIENCY (%)
+
V
IN
C1
15µF
SHDN
LT1613
SHDN
GND
SW
R1
37.4k
+
C2
22µF
85
80
75
70
65
V
IN
= 1.5V
V
IN
= 2.8V
V
IN
= 3.5V
FB
R2
12.1k
L1: MURATA LQH3C4R7M24 OR SUMIDA CD43-4R7
C1: AVX TAJA156M010
C2: AVX TAJB226M006
D1: MBR0520
60
1613 TA01
55
50
0
50
100 150 200 250 300 350 400
LOAD CURRENT (mA)
1613 TA01a
Figure 1. 3.3V to 5V 200mA DC/DC Converter
U
Efficiency Curve
V
IN
= 4.2V
U
U
1
LT1613
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW
SW 1
GND 2
FB 3
4 SHDN
5 V
IN
V
IN
Voltage .............................................................. 10V
SW Voltage ................................................– 0.4V to 36V
FB Voltage ..................................................... V
IN
+ 0.3V
Current into FB Pin ...............................................
±1mA
SHDN Voltage .......................................................... 10V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range
Commercial ............................................. 0°C to 70°C
Extended Commercial (Note 2) ........... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LT1613CS5
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S5 PART MARKING
LTED
Consult factory for Industrial and Military grade parts.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Commercial grade 0°C to 70°C, V
IN
= 1.5V, V
SHDN
= V
IN
unless
otherwise noted. (Note 2)
PARAMETER
Minimum Operating Voltage
Maximum Operating Voltage
Feedback Voltage
FB Pin Bias Current
Quiescent Current
Quiescent Current in Shutdown
Reference Line Regulation
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Pin Bias Current
V
SHDN
= 3V
V
SHDN
= 0V
25
0.01
(Note 3)
I
SW
= 300mA
V
SW
= 5V
1
0.3
50
0.1
V
SHDN
= 1.5V
V
SHDN
= 0V, V
IN
= 2V
V
SHDN
= 0V, V
IN
= 5V
1.5V
≤
V
IN
≤
10V
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP
0.9
MAX
1.1
10
1.255
80
4.5
0.5
1.0
0.2
1.8
UNITS
V
V
V
nA
mA
µA
µA
%/V
MHz
%
mA
1.205
1.23
27
3
0.01
0.01
0.02
1.0
82
550
1.4
86
800
300
0.01
350
1
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1613C is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
2
U
W
U
U
W W
W
mV
µA
V
V
µA
µA
LT1613
TYPICAL PERFOR A CE CHARACTERISTICS
Switch V
CESAT
vs Switch Current
700
600
500
T
A
= 25°C
2.00
1.75
V
IN
= 5V
SHDN PIN BIAS CURRENT (µA)
40
SWITCHING FREQUENCY (MHz)
V
CESAT
(mV)
400
300
200
100
0
0
100
200 300 400 500
SWITCH CURRENT (mA)
600
700
Current Limit vs Duty Cycle
1000
900
CURRENT LIMIT (mA)
800
70°C
700
600
500
400
300
200
10
20
30
40
50
60
DUTY CYCLE (%)
70
80
–40°C
25°C
FEEDBACK PIN VOLTAGE (V)
U W
Oscillator Frequency vs
Temperature
50
SHDN Pin Current vs V
SHDN
T
A
= 25°C
1.50
1.25
1.00
0.75
0.50
0.25
0
–50
V
IN
= 1.5V
30
20
10
0
–25
0
25
50
TEMPERATURE (°C)
75
100
1613 G02
0
1
2
3
4
SHDN PIN VOLTAGE (V)
5
1613 G03
1613 G01
Feedback Pin Voltage
1.25
1.24
VOLTAGE
1.23
1.22
1.21
1.20
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1613 G05
1613 G04
Switching Waveforms, Circuit of Figure 1
V
OUT
100mV/DIV
AC COUPLED
V
SW
5V/DIV
I
SW
200mA/DIV
I
LOAD
= 150mA
200ns/DIV
1613 G06
3
LT1613
PIN FUNCTIONS
SW (Pin 1):
Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to keep EMI down.
GND (Pin 2):
Ground. Tie directly to local ground plane.
FB (Pin 3):
Feedback Pin. Reference voltage is 1.23V.
Connect resistive divider tap here. Minimize trace area at
FB. Set V
OUT
according to V
OUT
= 1.23V(1 + R1/R2).
SHDN (Pin 4):
Shutdown Pin. Tie to 1V or more to enable
device. Ground to shut down.
V
IN
(Pin 5):
Input Supply Pin. Must be locally bypassed.
BLOCK DIAGRAM
V
IN
5
R5
40k
V
OUT
R1
(EXTERNAL)
FB
Q1
3
–
Q2
x10
R3
30k
R4
140k
FB
C
C
R2
(EXTERNAL)
1.4MHz
OSCILLATOR
SHDN
4
SHUTDOWN
OPERATIO
The LT1613 is a current mode, internally compensated,
fixed frequency step-up switching regulator. Operation
can be best understood by referring to the Block Diagram.
Q1 and Q2 form a bandgap reference core whose loop is
closed around the output of the regulator. The voltage
drop across R5 and R6 is low enough such that Q1 and Q2
do not saturate, even when V
IN
is 1V. When there is no
load, FB rises slightly above 1.23V, causing V
C
(the error
amplifier’s output) to decrease. Comparator A2’s output
stays high, keeping switch Q3 in the off state. As increased
output loading causes the FB voltage to decrease, A1’s
output increases. Switch current is regulated directly on a
cycle-by-cycle basis by the V
C
node. The flip flop is set at
the beginning of each switch cycle, turning on the switch.
When the summation of a signal representing switch
current and a ramp generator (introduced to avoid
subharmonic oscillations at duty factors greater than
50%) exceeds the V
C
signal, comparator A2 changes
state, resetting the flip flop and turning off the switch.
More power is delivered to the output as switch current is
increased. The output voltage, attenuated by external
resistor divider R1 and R2, appears at the FB pin, closing
the overall loop. Frequency compensation is provided
internally by R
C
and C
C
. Transient response can be opti-
mized by the addition of a phase lead capacitor C
PL
in
parallel with R1 in applications where large value or low
ESR output capacitors are used.
As the load current is decreased, the switch turns on for a
shorter period each cycle. If the load current is further
decreased, the converter will skip cycles to maintain
output voltage regulation.
4
+
R
C
RAMP
GENERATOR
Σ
–
W
U
U
U
U
V
IN
R6
40k
+
A1
g
m
1 SW
COMPARATOR
FF
S
DRIVER
Q
Q3
A2
R
+
0.15Ω
–
2 GND
1613 • BD
LT1613
OPERATIO
LAYOUT
The LT1613 switches current at high speed, mandating
careful attention to layout for proper performance.
You
will not get advertised performance with careless layouts.
Figure 2 shows recommended component placement for
a boost (step-up) converter. Follow this closely in your
PCB layout. Note the direct path of the switching loops.
Input capacitor C1
must
be placed close (< 5mm) to the IC
package. As little as 10mm of wire or PC trace from C
IN
to
V
IN
will cause problems such as inability to regulate or
oscillation.
The ground terminal of output capacitor C2 should tie
close to Pin 2 of the LT1613. Doing this reduces dI/dt in the
ground copper which keeps high frequency spikes to a
minimum. The DC/DC converter ground should tie to the
PC board ground plane at one place only, to avoid intro-
ducing dI/dt in the ground plane.
A SEPIC (single-ended primary inductance converter)
schematic is shown in Figure 3. This converter topology
produces a regulated output voltage that spans (i.e., can
be higher or lower than) the output. Recommended com-
ponent placement for a SEPIC is shown in Figure 4.
V
OUT
D1
+
C2
VIAS TO
GROUND
PLANE
R2
GROUND
Figure 2. Recommended Component Placement for Boost
Converter. Note Direct High Current Paths Using Wide PCB
Traces. Minimize Area at Pin 3 (FB). Use Vias to Tie Local
Ground Into System Ground Plane. Use Vias at Location Shown
to Avoid Introducing Switching Currents Into Ground Plane
U
V
IN
4V TO
7V
L1A
22µH
C3
1µF
+
C1
15µF
V
IN
LT1613
SW
R1
100k
FB
GND
R2
32.4k
L1B
22µH
D1
SHDN
SHDN
+
V
OUT
5V/150mA
C2
15µF
C1, C2: AVX TAJA156M016
C3: TAIYO YUDEN JMK325BJ226MM
D1: MOTOROLA MBR0520
L1, L2: MURATA LQH3C220
1613 F03
Figure 3. Single-Ended Primary Inductance Converter (SEPIC)
Generates 5V from An Input Voltage Above or Below 5V
L1B
V
OUT
D1
C3
L1A
+
C1
V
IN
+
C2
1
5
2
SHUTDOWN
3
VIAS TO
GROUND
PLANE
R2
4
L1
+
C1
V
IN
GROUND
R1
1613 F04
Figure 4. Recommended Component Placement for SEPIC
1
5
COMPONENT SELECTION
SHUTDOWN
2
3
4
Inductors
Inductors used with the LT1613 should have a saturation
current rating (where inductance is approximately 70% of
zero current inductance) of approximately 0.5A or greater.
DCR of the inductors should be 0.5Ω or less. For boost
converters, inductance should be 4.7µH for input voltage
less than 3.3V and 10µH for inputs above 3.3V. When
using the device as a SEPIC, either a coupled inductor or
two separate inductors can be used. If using separate
inductors, 22µH units are recommended for input voltage
above 3.3V. Coupled inductors have a beneficial mutual
inductance, so a 10µH coupled inductor results in the
same ripple current as two 20µH uncoupled units.
R1
1613 F02
5
