Linear Technology LT1300 User manual

1
LT1300
■
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
■
Palmtop Computers
■
Portable Instruments
■
Bar-Code Scanners
■
DC/DC Converter Module Replacements
■
Battery Backup Supplies
■
Personal Digital Assistants
■
PCMCIA Cards
TheLT1300isamicropowerstep-upDC/DCconverterthat
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-
loadquiescentcurrentof120µAandashutdownpinwhich
reducessupplycurrentto10µA.Theon-chippowerswitch
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-
facemountinductorsandcapacitors.Operationisguaran-
teedat 1.8V input. This allows more energytobeextracted
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
LT1300is available in an8-leadSOIC package, minimizing
board space requirements. For a 5V/12V Selectable Out-
put Converter see the LT1301. For increased output cur-
rent see the LT1302.
DESCRIPTION
U
FEATURES
TYPICAL APPLICATIONS N
U
Micropower High Efficiency
3.3/5V Step-Up DC/DC Converter
APPLICATIONS
U
Two-Cell to 3.3V/5V Step-Up Converter 5V Output Efficiency
L1 = COILCRAFT DO1608-103
OR SUMIDA CD54-100
C1 = AVX TPSD107M010R0100
OR SANYO OS-CON 16SA100M
D1 =MBRS130LT3
OR 1N5817
C1
100µF

5V/3.3V
OUTPUT
++
L1
10µH D1
C1
100µF
2×
AA
CELL
SW
I
LIM
PGND GND
SENSE
LT1300
SELECT
LT1300 TA1
5V/3.3V
SELECT
SHDN
SHUTDOWN N/C
2
67
4
5
81
3
V
IN

LOAD CURRENT (mA)
10 100 500
LT1300 TA2
1
74
EFFICIENCY (%)
76
78
80
82
90
84
86
88 V
IN
= 4.0V
V
IN
= 3.0V
V
IN
= 2.5V
V
IN
= 2.0V
Burst Mode is a trademark of Linear Technology Corporation.

2
LT1300
ORDER PART
NUMBER
ABSOLUTE MAXIMUMRATINGS
W
WW
U
PACKAGE/ORDER INFORMATION
W
UU
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
S8 PART MARKING
T
JMAX
= 100°C, θ
JA
= 150°C/W 1300
LT1300CN8
LT1300CS8
Consult factory for Industrial grade parts.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
Quiescent Current V
SHDN
= 0.5V, V
SEL
= 5V, V
SENSE
= 5.5V ●120 200 µA
V
SHDN
= 1.8V ●715 µA
V
IN
Input Voltage Range 1.8 V
●2.0 V
V
OUT
Output Sense Voltage V
SEL
= 5V ●4.80 5.0 5.20 V
V
SEL
= 0V ●3.15 3.3 3.45 V
Output Referred V
SEL
= 5V (Note 1) ●22 50 mV
Comparator Hysteresis V
SEL
= 0V (Note 1) ●14 35 mV
Oscillator Frequency Current Limit not Asserted. See Test Circuit. 120 155 185 kHz
Oscillator TC 0.2 %/°C
DC Maximum Duty Cycle 75 86 95 %
t
ON
Switch On Time Current Limit not Asserted. 5.6 µs
Output Line Regulation 1.8V < V
IN
< 6V ●0.06 0.15 %/V
V
CESAT
Switch Saturation Voltage I
SW
= 700mA ●130 200 mV
Switch Leakage Current V
SW
= 5V, Switch Off ●0.1 10 µA
Peak Switch Current I
LIM
Floating (See Typical Application) 0.75 1.0 1.25 A
(Internal Trip Point) I
LIM
Grounded 0.4 A
V
SHDNH
Shutdown Pin High ●1.8 V
V
SHDNL
Shutdown Pin Low 0.5 V
V
SELH
Select Pin High ●1.5 V
V
SELL
Select Pin Low ●0.8 V
I
SHDN
Shutdown Pin Bias Current V
SHDN
= 5V ●920 µA
V
SHDN
= 2V ●3µA
V
SHDN
= 0V ●0.1 1 µA
I
SEL
Select Pin Bias Current 0V < V
SEL
< 5V ●13 µA
ELECTRICAL CHARACTERISTICS
TA= 25°C, VIN = 2V unless otherwise noted.
Note 1: Hysteresis specified is DC. Output ripple may be higher if
output capacitance is insufficient or capacitor ESR is excessive. See
applications section.
The ●denotes specifications which apply over the 0°C to 70°C
temperature range.
1
2
3
4
8
7
6
5

TOP VIEW
GND
SEL
SHDN
SENSE
PGND
SW
V
IN
I
LIM
N8 PACKAGE
8-LEAD PLASTIC DIP

S8 PACKAGE
8-LEAD PLASTIC SOIC

3
LT1300
TYPICAL PERFORMANCE CHARACTERISTICS
UW
No-Load Battery Current Total Quiescent Current in Shutdown
SWITCH CURRENT (A)
0 0.1
V
CESAT
(mV)
150
125
200
175
250
225
0.8 0.9
LT1300 G5
100
75
50
25
00.2 0.3 0.4 0.5 0.6 0.7 1
Maximum Output Current
vs Input Voltage
Maximum Output Current
vs Input Voltage
200µs/DIV
0
Transient Response
VIN = 2V, VOUT = 5V Startup Response
VCESAT vs ISW
Efficiency
Shutdown Pin Bias Current
V
OUT
100mV/DIV
AC COUPLED V
OUT
1V/DIV
V
SHDN
10V/DIV
LT1300 G8
SHUTDOWN VOLTAGE (V)
0
0
SHUTDOWN CURRENT (µA)
2
6
8
10
20
14
245
LT1300 G4
4
16
18
12
13 6
7
8
T
A
= 25°C
LOAD CURRENT (mA)
1
74
EFFICIENCY (%)
76
78
80
82
10 100 1000
LT1300 G1
72
70
68
66
84
86
88
V
IN
= 3V
V
IN
= 2V
V
IN
= 2.5V
V
OUT
= 3.3V
L = 10µH
INPUT VOLTAGE (V)
1.4
INPUT CURRENT (µA)
150
145
160
155
170
165
3.02.8
LT1300 G2
140
135
130
125
120 1.81.6 2.22.0 2.62.4 3.43.2
V
OUT
= 5V
V
OUT
= 3.3V
INPUT VOLTAGE (V)
0
I
SHDN
+I
VIN
+I
SENSE
(µA)
40
50
60
8
LT1300 G3
30
20
0246
10
80
70
1357
INPUT VOLTAGE (V)
1.5
OUTPUT CURRENT (mA)
500
600
700
34
LT1300 G6
400
300
22.5 3.5 4.5
200
100
0
V
OUT
= 5V,
I
LIM
FLOATING
L = 22µH
COILCRAFT
DO3316-223 L = 10µH
COILCRAFT
DO1608-103
INPUT VOLTAGE (V)
1.5
0
LOAD CURRENT (mA)
100
300
400
500
2.5 3 3.5
900
LT1300 G7
200
2
600
700
800
L = 10µH
VOUT = 3.3V
ILIM FLOATING
V
OUT
= 5V
R
LOAD
= 20Ω
LT1300 G9
500µs/DIV
200mA
I
LOAD

4
LT1300
PINFUNCTIONS
UUU
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(Pin3):Shutdown.Pull highto effectshutdown. Tie
to ground for normal operation.
Sense (Pin 4): “Output” Pin.
I
LIM
(Pin5):Floatfor1Aswitchcurrentlimit. 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.
Figure 1.
BLOCK DIAGRAM
W
OSCILLATOR
155kHZ
R2
730Ω
C2

SW
R1
3Ω
Q2
1x
Q1
160x
18mV
OFF
V
IN
V
IN
I
LIM
PGND
V
OUT
ENABLE
A1
COMPARATOR
–
+
++
–
+
1.25V
REFERENCE

L1 D1
7
2
4
SENSE
A2 CURRENT 
COMPARATOR
A3 DRIVER
BIAS Q3
8.5k
58
SHUTDOWN
3
SELECT
2
GND
161k
144k
500k
C1
1
LT1300 F1

5
LT1300
TEST CIRCUIT
S

Oscillator Test Circuit
OPERATION
U
20µs/DIV
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
fullload output current is acceptable. Lower peakcurrents
also extend alkaline battery life due to the alkaline cell’s
highinternalimpedance.Typical operatingwaveforms are
shown in Figure 3.
Operationofthe 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-dividerratio,ishigherthatthe1.25Vreferencevoltage,
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,
whichevercomesfirst.Afterafixedoff-timeof(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.
Ifswitch current reaches 1A, causing A2 totrip,switchon-
timeisreducedandoff-timeincreasesslightly.Thisallows
continuous mode operation during bursts. Current com-
parator A2 monitors the voltage across 3Ωresistor R1
which is directly related to inductor L1’s current. Q2’s
collector current is set by the emitter-area ratio to 0.6%
ofQ1’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 Figure 3. Burst Mode Operation in Action
TRACE B
500mA/DIV
I
LIM
PIN
GROUNDED
LT1300 F2
Figure 2. Switch Pin Current With ILIM Floating or Grounded
TRACE A
500mA/DIV
I
LIM
PIN
OPEN
V
OUT
20mV/DIV
AC COUPLED
V
SW
5V/DIV
I
SW
IA/DIV
20µS/DIV LT1300 F2
2V
100µF
V
IN
SEL
SENSE
GND PGND
SHDN
SW
LT1300
I
L
100Ω
5V
f
OUT

6
LT1300
APPLICATIONS INFORMATION
WUU U
Output Voltage Selection
The LT1300 can be selected to 3.3V or 5V under logic
control or fixed at either by tying SELECT to ground or V
IN
respectively. It is permissible to tie SELECT to a voltage
higher than V
IN
as long as it does not exceed 10V.
Efficiencyin3.3Vmodewillbeslightlylessthat in5Vmode
due to the fact that the diode drop is a greater percentage
of 3.3V than 5V. Since the bipolar switch in the LT1300
gets its base drive from V
IN
, no reduction in switch
efficiency occurs when in 3.3V mode. When V
IN
exceeds
the programmed output voltage the output will follow the
input. This is characteristic of the simple step-up or
“boost” converter topology. A circuit example that pro-
vides a regulated output with an input voltage above or
below the output (called a buck-boost or SEPIC) is shown
in the Typical Applications section.
Shutdown
The converter can be turned off by pulling SHDN (pin 3)
high. Quiescent current drops to 10µA in this condition.
Bias current of 3µA to 5µA flows into the pin (at 2.5V input).
It is recommended that SHDN not be left floating. Tie the
pin to ground if the feature is not used.
I
LIM
Function
The LT1300’s current limit (I
LIM
) pin can be used for soft
start. Upon start-up, switching regulators require maxi-
mum current from the supply. The high currents flowing
can create IR drops along supply and ground lines and
are especially demanding on alkaline batteries. By in-
stalling an R1 and C3 as shown in Figure 4, the switch
current in the LT1300 is limited to 400mA until the 15µA
flowing out of the I
LIM
pin charges up the 0.1µF capaci-
tor. Input current is held to under 500mA while the
output voltage ramps up to 5V as shown in Figure 5. The
1Meg resistor provides a discharge path for the capacitor
withoutappreciablydecreasingpeakswitchcurrent.When
the full capability of the LT1300 is not required, peak
current can be reduced by changing the value of R3 as
shown in Figure 6. With R3 = 0, switch current is limited
to approximately 400mA.
Figure 4. Addition of R1 and C3 Limit Input Current at Startup
500µs/DIV
REP RATE = 1Hz
LT1300 F5
V
OUT
2VDIV
I
BATTERY
500mA/DIV
V
SHDN
10V/DIV
C2
100µF

C3
0.1µF

R1
1M
5V/3.3V
OUTPUT
+
+
L1
10µH D1
C1
100µF
SW
I
LIM
PGND GND
SENSE
LT1300
SHDN
SELECT
V
IN
Figure 5. Startup Waveforms using Soft-Start Circuitry
ILOAD = 100mA, VOUT = 5V
R
LIM
(Ω)
500
SWITCH CURRENT (mA)
700
800
1000
1100
100 10k 100k 1M
LT1300 F1B
300 1k
900
600
400
1.6V ≤VIN ≤5V
Figure 6. Peak Switch Current vs. RLIM

7
LT1300
COMPONENT
PART NUMBER VENDOR L ( µ H) DCR (Ω)I
LIM
PIN 50mA LOAD 200mA LOAD HEIGHT (mm) PHONE NUMBER
DO1608-103 Coilcraft 10 0.11 Float 83 83 3.5 (708) 639–6400
DO3316-223 Coilcraft 22 0.050 Float 85 85 5.5
DO1608-223 Coilcraft 22 0.31 Ground 85 — 3.5
CTX10-1 Coiltronics 10 0.038 Float 85 85 4.2 (407) 241–7876
CTX20-1 Coiltronics 20 0.175 Ground 86 — 4.2
LQH3C2204K0M00 Murata-Frie 22 0.7 Ground 81 — 2.0 (404) 436–1300
CD54-100M Sumida 10 0.11 Float 85 85 4.5 (708) 956–0666
CDRH62-220M Sumida 22 0.38 Ground 84 — 3.0
CDRH62-100M Sumida 10 0.17 Float 81 82 3.0
GA10-102K Gowanda 10 0.038 Float 85 86 6.6 Through-Hole (716) 532–2234
APPLICATIONS INFORMATION
WUU U
Table 1. Recommended Inductors
Inductor Selection
For full output power, the inductor should have a satura-
tion current rating of 1.25A for worst-case current limit,
although it is acceptable to bias an inductor 20% or more
into saturation. Smaller inductors can be used in conjunc-
tion with the I
LIM
pin. Efficiency is significantly affected by
inductor DCR. For best efficiency limit the DCR to 0.03Ω
or less. Toroidal types are preferred in some cases due to
their closed design and inherent EMI/RFI superiority.
Recommended inductors are listed in Table 1.
Capacitor Selection
LowESR capacitors are required forbothinput and output
of the LT1300. ESR directly affects ripple voltage and
efficiency.Forsurface mount applications AVX TPS series
tantalum capacitors are recommended. These have been
specially designed for SMPS and have low ESR along with
high surge current ratings. For through-hole application
Sanyo OS-CON capacitors offer extremely low ESR in a
small size. Again, if peak switch current is reduced using
the I
LIM
pin, capacitor requirements can be relaxed and
smaller, higher ESR units can be used. Low frequency
output ripple can be reduced by adding multiple output
capacitors. If capacitance is reduced, output ripple will
increase. Suggested capacitor sources are listed in Table 2.
Table 2. Recommended Capacitors
VENDOR SERIES TYPE PHONE#
AVX TPS Surface Mount (803)448–9411
Sanyo OS-CON Through-Hole (619) 661–6835
Panasonic HFQ Through-Hole (201) 348–5200
Diode Selection
Best performance is obtained with a Schottky rectifier
diode such as the 1N5817. Phillips Components makes
this in surface mount as the PRLL5817. Motorola makes
the MBRS130LT3 which is slightly better and also in
surface mount. For lower output power a 1N4148 can be
used although efficiency will suffer substantially.
Layout Considerations
The LT1300 is a high speed, high current device. The input
capacitor must be no more than 0.2" from V
IN
(pin 6) and
ground. Connect the PGND and GND (pins 8 and 1)
together under the package. Place the inductor adjacent to
SW (pin 7) and make the switch pin trace as short as
possible. This keeps radiated noise to a minimum.
EFFICIENCY 2.5V
IN
, 5V
OUT
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 represen-
tationthattheinterconnectionofitscircuitsas described herein will not infringeonexistingpatentrights.

8
LT1300
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
[phone]
●
FAX : [phone]
●
TELEX : 499-3977
1234
0.150 – 0.
(3.810 – 3.
8765
0.189 – 0.197*
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
0.016 – 0.050
0.406 – 1.270
0.010 – 0.020
(0.254 – 0.508)×45°
0°– 8° TYP
0.008 – 0.010
(0.203 – 0.254)
SO8 0294
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
S8 Package
8-Lead Plastic S0IC
TYPICAL APPLICATIONS N
U
 LINEAR TECHNOLOGY CORPORATION 1994
LT/GP 0394 10K • PRINTED IN USA
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters) unless otherwise noted.
Four-Cell to 5V/3.3V Up-Down Converter
N8 Package
8-Lead Plastic DIP
N8 0392
0.009 – 0.015
(0.229 – 0.381)
0.300 – 0.320
(7.620 – 8.128)
0.325 +0.025
–0.015
+0.635
–0.381
8.255
()
0.045 ± 0.015
(1.143 ± 0.381)
0.100 ± 0.010
(2.540 ± 0.254)
0.065
(1.651)
TYP
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
0.020
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
0.125
(3.175)
MIN
12 34
8765
0.250 ± 0.010
(6.350 ± 0.254)


0.400
(10.160)
MAX
+
100µF
22µF
35V
CONTRAST 
VOUT –4V TO –29V 12mA
MAXIMUM FROM 1.8V SUPPLY 
(77% EFFICIENT)
20mA MAXIMUM FROM 
3V SUPPLY (83% EFFICIENT)
2.2µF
SW
PWM IN
0% TO 100%
CMOS DRIVE 0V TO 5V
150K
12K
12K
1
10 8
2
9
3
7
4
I
LIM
PGND GND
SENSE
LT1300
SELECT
LT1300 TA6
1N5819
T1
T1 = DALE LPE-5047-AO45 [phone]
SHDN SHUTDOWN
N/C
N/C
V
IN
V
IN
1.8V TO 6V
+
+
1N5817 2N4403
5V, 200mA
+
L1*
10µH
*SUMIDA CD54-100LC 
COILCRAFT DO3316-223
100µF
100µF
470Ω
0.1µF
2×
AA
CELL SW
ILIM
PGND
GND
SENSE
LT1300
SELECT
LT1300 TA5
SHDN
NC
SHUTDOWN
VIN

+
Step-Up Converter with Automatic Output Disconnect
LCD Contrast Supply
1N5817
5V/3.3V
220mA
80% EFFICIENT
+
L1*
27µH
*L1, L2 = GOWANDA GA20-272K
COILCRAFT DO3316-273K
SUMIDA CD73-270K
**C1, C2, C3 = SANYO OS-CON 16SA100M
L2*
27µH
C1**
100µF
C2**
100µF
C3**
100µF
4×
AA
CELL
SW
I
LIM
PGND
GND
SENSE
LT1300
SELECT
LT1300 TA3
5V/3.3V
2.5V ≤V
IN
≤8V
SHDN
SHUTDOWN
N/C
V
IN

+
+