LT1300
Micropower High Efficiency
3.3/5V Step-Up DC/DC Converter
FEATURES
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DESCRIPTION
The LT1300 is a micropower step-up DC/DC converter that
utilizes Burst Mode™ operation. The device can deliver 5V
or 3.3V from a two-cell battery input. It features program-
mable 5V or 3.3V output via a logic-controlled input, no-
load quiescent current of 120µA and a shutdown pin which
reduces supply current to 10µA. The on-chip power switch
has a low 170mV saturation voltage at a switch current of
1A, a four-fold reduction over prior designs. A 155kHz
internal oscillator allows the use of extremely small sur-
face mount inductors and capacitors. Operation is guaran-
teed at 1.8V input. This allows more energy to be extracted
from the battery increasing operating life. The I
LIM
pin can
be used to program peak switch current with a single
resistor allowing the use of less expensive and smaller
inductors and capacitors in lighter load applications. The
LT1300 is available in an 8-lead SOIC package, minimizing
board space requirements. For a 5V/12V Selectable Out-
put Converter see the LT1301. For increased output cur-
rent see the LT1302.
Burst Mode is a trademark of Linear Technology Corporation.
Up to 220mA Output Current at 5V from 2V Supply
Supply Voltage as Low as 1.8V
Up to 88% Efficiency
Small Inductor –10µH
120µA Quiescent Current
Shutdown to 10µA
Programmable 3.3V or 5V Output
I
LIM
Pin Programs Peak Switch Current
Low V
CESAT
Switch: 170mV at 1A Typical
Uses Inexpensive Surface Mount Inductors
8-Lead DIP or SOIC Package
APPLICATIONS
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Palmtop Computers
Portable Instruments
Bar-Code Scanners
DC/DC Converter Module Replacements
Battery Backup Supplies
Personal Digital Assistants
PCMCIA Cards
TYPICAL APPLICATIONS
N
Two-Cell to 3.3V/5V Step-Up Converter
L1
10µH
6
V
IN
5V/3.3V 2
SELECT
SELECT
LT1300
3
SHDN
PGND
8
I
LIM
GND
1
5
N/C
7
SW
SENSE
4
86
EFFICIENCY (%)
5V Output Efficiency
5V/3.3V
OUTPUT
90
88
V
IN
= 4.0V
V
IN
= 3.0V
V
IN
= 2.5V
V
IN
= 2.0V
D1
2×
AA
CELL
+
C1
100µF
SHUTDOWN
+
C1
100µF
84
82
80
78
L1 = COILCRAFT DO1608-103
OR SUMIDA CD54-100
C1 = AVX TPSD107M010R0100
OR SANYO OS-CON 16SA100M
D1 = MBRS130LT3
OR 1N5817
LT1300 TA1
76
74
1
10
100
LOAD CURRENT (mA)
500
LT1300 TA2
U
U
U
1
LT1300
ABSOLUTE
MAXIMUM
RATINGS
V
IN
Voltage .............................................................. 10V
SW1 Voltage ............................................................ 20V
Sense Voltage .......................................................... 10V
SHUTDOWN Voltage................................................ 10V
SELECT Voltage ....................................................... 10V
I
LIM
Voltage ............................................................ 0.5V
Maximum Power Dissipation ............................. 500mW
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
GND 1
SEL 2
SHDN 3
SENSE 4
N8 PACKAGE
8-LEAD PLASTIC DIP
8
7
6
5
PGND
SW
V
IN
I
LIM
ORDER PART
NUMBER
LT1300CN8
LT1300CS8
S8 PART MARKING
1300
S8 PACKAGE
8-LEAD PLASTIC SOIC
T
JMAX
= 100°C,
θ
JA
= 150°C/ W
Consult factory for Industrial grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
Quiescent Current
I
Q
V
IN
V
OUT
Input Voltage Range
T
A
= 25°C, V
IN
= 2V unless otherwise noted.
MIN
q
q
q
CONDITIONS
V
SHDN
= 0.5V, V
SEL
= 5V, V
SENSE
= 5.5V
V
SHDN
= 1.8V
TYP
120
7
MAX
200
15
Output Sense Voltage
Output Referred
Comparator Hysteresis
Oscillator Frequency
Oscillator TC
Maximum Duty Cycle
Switch On Time
Output Line Regulation
Switch Saturation Voltage
Switch Leakage Current
Peak Switch Current
(Internal Trip Point)
Shutdown Pin High
Shutdown Pin Low
Select Pin High
Select Pin Low
Shutdown Pin Bias Current
V
SEL
= 5V
V
SEL
= 0V
V
SEL
= 5V (Note 1)
V
SEL
= 0V (Note 1)
Current Limit not Asserted. See Test Circuit.
q
q
q
q
1.8
2.0
4.80
3.15
120
75
DC
t
ON
V
CESAT
Current Limit not Asserted.
1.8V < V
IN
< 6V
I
SW
= 700mA
V
SW
= 5V, Switch Off
I
LIM
Floating (See Typical Application)
I
LIM
Grounded
q
q
q
0.75
q
q
q
5.0
3.3
22
14
155
0.2
86
5.6
0.06
130
0.1
1.0
0.4
5.20
3.45
50
35
185
95
0.15
200
10
1.25
V
SHDNH
V
SHDNL
V
SELH
V
SELL
I
SHDN
1.8
0.5
1.5
9
3
0.1
1
0.8
20
1
3
I
SEL
Select Pin Bias Current
V
SHDN
= 5V
V
SHDN
= 2V
V
SHDN
= 0V
0V < V
SEL
< 5V
q
q
q
q
UNITS
µA
µA
V
V
V
V
mV
mV
kHz
%/
°C
%
µs
%/V
mV
µA
A
A
V
V
V
V
µA
µA
µA
µA
The
q
denotes specifications which apply over the 0°C to 70°C
temperature range.
Note 1:
Hysteresis specified is DC. Output ripple may be higher if
output capacitance is insufficient or capacitor ESR is excessive. See
applications section.
2
U
W
U
U
W W
W
LT1300
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency
88
84
INPUT CURRENT (µA)
V
OUT
= 3.3V
86
L = 10µH
82
EFFICIENCY (%)
I
SHDN
+
I
VIN
+
I
SENSE
(µA)
80
78
76
74
72
70
68
66
1
V
IN
= 3V
V
IN
= 2.5V
V
IN
= 2V
10
100
LOAD CURRENT (mA)
Shutdown Pin Bias Current
20
18
SHUTDOWN CURRENT (µA)
T
A
= 25°C
16
14
12
10
8
6
4
2
0
0
1
6
4
3
2
5
SHUTDOWN VOLTAGE (V)
7
8
V
CESAT
(mV)
OUTPUT CURRENT (mA)
Maximum Output Current
vs Input Voltage
900
800
700
LOAD CURRENT (mA)
VOUT = 3.3V
ILIM FLOATING
600
500
400
300
200
100
0
1.5
2
L = 10µH
3
2.5
INPUT VOLTAGE (V)
U W
LT1300 G1
LT1300 G4
LT1300 G7
No-Load Battery Current
170
165
160
155
150
145
140
135
130
125
V
OUT
= 3.3V
V
OUT
= 5V
80
70
60
50
40
30
20
10
0
Total Quiescent Current
in Shutdown
1000
120
1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
INPUT VOLTAGE (V)
LT1300 G2
0
1
2
4
5
6
3
INPUT VOLTAGE (V)
7
8
LT1300 G3
V
CESAT
vs I
SW
250
225
200
175
150
125
100
75
50
25
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
SWITCH CURRENT (A)
LT1300 G5
Maximum Output Current
vs Input Voltage
700
600
500
400
300
200
100
0
1.5
V
OUT
= 5V,
I
LIM
FLOATING
L = 22µH
COILCRAFT
DO3316-223
L = 10µH
COILCRAFT
DO1608-103
2
3.5
3
2.5
INPUT VOLTAGE (V)
4
4.5
LT1300 G6
Transient Response
V
IN
= 2V, V
OUT
= 5V
V
OUT
100mV/DIV
AC COUPLED
200mA
0
200µs/DIV
V
OUT
1V/DIV
Startup Response
I
LOAD
V
SHDN
10V/DIV
500µs/DIV
V
OUT
= 5V
R
LOAD
= 20Ω
LT1300 G8
LT1300 G9
3.5
3
LT1300
PIN FUNCTIONS
GND (Pin 1):
Signal Ground.
Sel (Pin 2):
Output Select. When tied to V
IN
or V
OUT
converter regulates at 5V. When grounded converter
regulates at 3.3V.
SHDN (Pin 3):
Shutdown. Pull high to effect shutdown. Tie
to ground for normal operation.
Sense (Pin 4):
“Output” Pin.
I
LIM
(Pin 5):
Float for 1A switch current limit. Tie to ground
for approximately 400mA. A resistor between I
LIM
and
ground sets peak current to some intermediate value (see
Figure 5).
V
IN
(Pin 6):
Supply Pin. Must be bypassed with a large
value electrolytic to ground. A 0.1µF ceramic capacitor
close to the pin may be needed in some cases.
SW (Pin 7):
Switch Pin. Connect inductor and diode here.
Keep layout short and direct to minimize electronic radia-
tion.
PGND (Pin 8):
Power Ground. Tie to signal ground (pin 1)
under the package. Bypass capacitor from V
IN
should be
tied directly to the pin.
BLOCK DIAGRAM
V
IN
+
C1
1.25V
REFERENCE
144k
4
W
U
U
U
L1
D1
V
OUT
+
C2
SENSE
4
2
V
IN
7
SW
18mV
A2 CURRENT
COMPARATOR
500k
+
R2
730Ω
R1
3Ω
–
A1
COMPARATOR
OFF
+
ENABLE OSCILLATOR
155kHZ
A3 DRIVER
–
BIAS
Q3
8.5k
Q2
1x
Q1
160x
161k
GND
1
2
SELECT
SHUTDOWN
3
5
I
LIM
PGND
8
LT1300 F1
Figure 1.
LT1300
TEST CIRCUITS
2V
Oscillator Test Circuit
5V
100Ω
V
IN
SEL
100µF
LT1300
I
L
SW
f
OUT
SENSE
GND
SHDN
PGND
OPERATION
Operation of the LT1300 is best understood by referring to
the Block Diagram in Figure 1. When A1’s negative input,
related to the Sense pin voltage by the appropriate resis-
tor-divider ratio, is higher that the 1.25V reference voltage,
A1’s output is low. A2, A3 and the oscillator are turned off,
drawing no current. Only the reference and A1 consume
current, typically 120µA. When the voltage at A1’s nega-
tive input decreases below 1.25V, overcoming A1’s 6mV
hysteresis, A1’s output goes high, enabling the oscillator,
current comparator A2, and driver A3. Quiescent current
increases to 2mA as the device prepares for high current
switching. Q1 then turns on in a controlled saturation for
(nominally) 5.3µs or until current comparator A2 trips,
whichever comes first. After a fixed off-time of (nominally)
1.2µs, Q1 turns on again. The LT1300’s switching causes
current to alternately build up in L1 and dump into capaci-
tor C2 via D1, increasing the output voltage. When the
output is high enough to cause A1’s output to go to low,
switching action ceases. C2 is left to supply current to the
load until V
OUT
decreases enough to force A1’s output
high, and the entire cycle repeats.
If switch current reaches 1A, causing A2 to trip, switch on-
time is reduced and off-time increases slightly. This allows
continuous mode operation during bursts. Current com-
parator A2 monitors the voltage across 3Ω resistor R1
which is directly related to inductor L1’s current. Q2’s
collector current is set by the emitter-area ratio to 0.6%
of Q1’s collector current. When R1’s voltage drop exceeds
18mV, corresponding to 1A inductor current, A2’s output
goes high, truncating the on-time portion of the oscillator
cycle and increasing off-time to about 2µs as shown in
Figure 2, trace A. This programmed peak current can be
TRACE A
500mA/DIV
I
LIM
PIN
OPEN
U
TRACE B
500mA/DIV
I
LIM
PIN
GROUNDED
20µs/DIV
LT1300 F2
Figure 2. Switch Pin Current With I
LIM
Floating or Grounded
reduced by tying the I
LIM
pin to ground, causing 15µA to
flow through R2 into Q3’s collector. Q3’s current causes
a 10.4mV drop in R2 so that only an additional 7.6mV is
required across R1 to turn off the switch. This corre-
sponds to a 400mA switch current as shown in Figure 2,
trace B. The reduced peak switch current reduces I
2
R
loses in Q1, L1, C1 and D1. Efficiency can be increased by
doing this provided that the accompanying reduction in
full load output current is acceptable. Lower peak currents
also extend alkaline battery life due to the alkaline cell’s
high internal impedance. Typical operating waveforms are
shown in Figure 3.
V
OUT
20mV/DIV
AC COUPLED
V
SW
5V/DIV
I
SW
IA/DIV
20µS/DIV
LT1300 F2
Figure 3. Burst Mode Operation in Action
5
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