1
LT1305
Micropower High Power
DC/DC Converter with
Low-Battery Detector
s
2-Cell and 3-Cell to 5V Conversion
s
EL Panel Drivers
s
Portable Instruments
U
S
A
O
PPLICATI
U
A
O
PPLICATI
TYPICAL
V
IN
LBI
SHDN
100k
1%
301k
1%
2 TO 3
CELLS
316k
1%
412k
1%
C1
220
µ
F
C2
220
µ
F
SHUTDOWN
LT1305
GND
PGND
FB
LBO
SW
D1
LT1305 · TA03
L1
10
µ
H
100k
+
C1, C2: AVX TPSE227010R0100
D1: MOTOROLA MBRS130LT3
L1: COILCRAFT D03316-103
V
OUT
5V
400mA
+
LOW BATTERY
GOES LOW AT
V
BAT
= 2.2V
LOAD CURRENT (mA)
1
EFFICIENCY (%)
80
90
10
100
1000
LT1305 · TA02
70
60
V
IN
= 4.00V
V
IN
= 3.00V
V
IN
= 2.00V
V
IN
= 2.50V
Efficiency
D
U
ESCRIPTIO
S
FEATURE
s
5V at 400mA from 2V Input
s
Supply Voltage As Low As 1.8V
s
120
µ
A Quiescent Current
s
Low-Battery Detector
s
Low V
CESAT
Switch: 310mV at 2A Typ
s
Uses Inexpensive Surface Mount Inductors
s
8-Lead SO Package
The LT
®
1305 is a micropower step-up DC/DC converter
that uses Burst Mode
TM
operation. Similar to the LT1303,
the LT1305 features a 2A internal low-loss switch and can
deliver up to four times the output power of the LT1303.
Quiescent current is only 120
µ
A and the Shutdown pin
further reduces current to 10
µ
A. A low-battery detector
provides an open-collector output that goes low when the
input voltage drops below a preset level. The LT1305 is
available in an 8-pin SO, easing board space requirements.
2-Cell and 3-Cell to 5V/400mA DC/DC Converter
with Low-Battery Detect
Burst Mode is a trademark of Linear Technology Corporation
, LTC and LT are registered trademarks of Linear Technology Corporation.
2
LT1305
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
W
U
U
PACKAGE/ORDER I FOR ATIO
V
IN
Voltage .............................................................. 10V
SW1 Voltage ............................................................ 25V
FB Voltage ............................................................... 10V
Shutdown Voltage ................................................... 10V
LBO Voltage ............................................................. 10V
LBI Voltage .............................................................. 10V
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
ORDER PART
NUMBER
Consult factory for Industrial and Military grade parts.
S8 PART MARKING
1305
LT1305CS8
T
JMAX
= 100
°
C,
JA
= 80
°
C/ W
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Q
Quiescent Current
V
SHDN
= 0.5V, V
FB
= 2V
q
120
200
µ
A
V
SHDN
= 1.8V
q
7
15
µ
A
V
IN
Input Voltage Range
1.8
1.55
V
q
2.0
V
Feedback Voltage
q
1.22
1.24
1.26
V
Comparator Hysteresis
q
6
12.5
mV
Feedback Pin Bias Current
V
FB
= 1V
q
7
20
nA
Oscillator Frequency
Current Limit Not Asserted
120
155
185
kHz
Oscillator TC
0.2
%/
°
C
DC
Maximum Duty Cycle
q
75
86
95
%
t
ON
Switch On Time
Current Limit Not Asserted
5.6
µ
s
Output Line Regulation
1.8V < V
IN
< 6V
q
0.06
0.15
%/V
V
CESAT
Switch Saturation Voltage
I
SW
= 1A
q
140
280
mV
Switch Leakage Current
V
SW
= 5V, Switch Off
q
0.1
10
µ
A
Peak Switch Current
V
IN
= 2V
1.35
2
2.35
A
q
1.20
2.50
A
V
IN
= 5V
1.15
2.15
A
LBI Trip Voltage
(Note 2)
q
1.21
1.24
1.27
V
LBI Input Bias Current
V
LBI
= 1V
q
7
20
nA
LBO Output Low
I
LOAD
= 100
µ
A
q
0.11
0.4
V
LBO Leakage Current
V
LBI
= 1.3V, V
LBO
= 5V
q
0.1
5
µ
A
V
SHDNH
Shutdown Pin High
q
1.8
V
V
SHDNL
Shutdown Pin Low
0.5
V
I
SHDN
Shutdown Pin Bias Current
V
SHDN
= 5V
q
8.0
20
µ
A
V
SHDN
= 2V
q
3.0
µ
A
V
SHDN
= 0V
q
0.1
1
µ
A
T
A
= 25
°
C, V
IN
= 2.0V, unless otherwise noted.
ELECTRICAL C
C
HARA TERISTICS
The
q
denotes specifications which apply over the 0
°
C to 70
°
C operating
temperature range.
Note 1: Hysteresis specified is DC. Output ripple may be higher if output
capacitance is insufficient or capacitor ESR is excessive.
Note 2: Low-battery detector comparator is inoperative when device is in
shutdown.
1
2
3
4
8
7
6
5
TOP VIEW
PGND
SW
V
IN
LBI
GND
LBO
SHDN
FB
S8 PACKAGE
8-LEAD PLASTIC SO
3
LT1305
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
TEMPERATURE (
°
C)
50
2
ON TIME (
µ
s)
3
4
5
6
8
25
0
25
50
LT1305 · G01
75
100
7
Switch On Time
TEMPERATURE (
°
C)
50
50
DUTY CYCLE (%)
60
65
70
75
80
85
25
0
25
50
LT1305 · G03
75
90
95
100
55
100
Maximum Duty Cycle
TEMPERATURE (
°
C)
50
100
FREQUENCY (kHz)
120
130
140
150
160
170
25
0
25
50
LT1305 · G02
75
180
190
200
110
100
Oscillator Frequency
TEMPERATURE (
°
C)
50
100
QUIESCENT CURRENT (
µ
A)
120
130
140
150
160
170
25
0
25
50
LT1305 · G04
75
180
190
200
110
100
SWITCH OFF
V
IN
= 2V
Quiescent Current
Quiescent Current
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (
µ
A)
300
400
500
8
LT1305 · G05
200
100
0
2
4
6
10
T
A
= 25
°
C
SWITCH OFF
Current Limit
TEMPERATURE (°C)
50
1.8
2.0
2.2
25
75
LT1305 · G06
1.6
1.4
25
0
50
100
1.2
1.0
PEAK SWITCH CURRENT (A)
2.4
TEMPERATURE (
°
C)
50
0
BIAS CURRENT (nA)
4
6
8
10
12
14
25
0
25
50
LT1305 · G07
75
16
18
20
2
100
LBI Pin Bias Current
FB Pin Bias Current
TEMPERATURE (
°
C)
50
0
BIAS CURRENT (nA)
4
6
8
10
12
14
25
0
25
50
LT1305 · G08
75
16
18
20
2
100
FB Voltage
TEMPERATURE (
°
C)
50
1.200
FEEDBACK VOLTAGE (V)
1.210
1.215
1.220
1.225
1.230
1.235
25
0
25
50
LT1305 · G09
75
1.240
1.245
1.250
1.205
100
4
LT1305
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
TEMPERATURE (
°
C)
50
1.200
LBI VOLTAGE (V)
1.210
1.215
1.220
1.225
1.230
1.235
25
0
25
50
LT1305 · G10
75
1.240
1.245
1.250
1.205
100
Low-Battery Detect Trip Point
TEMPERATURE (
°
C)
50
0
SWITCH SATURATION VOLTAGE (mV)
50
100
150
200
300
25
0
25
50
LT1305 · G13
75
100
250
I
SW
= 1A
Switch Saturation Voltage
SWITCH CURRENT (A)
0
SWITCH SATURATION VOLTAGE (mV)
300
400
1.6
LT1305 · F12
200
100
250
350
150
50
0
0.4
0.8
1.2
2.0
1.4
0.2
0.6
1.0
1.8
T
A
= 25
°
C
Switch Saturation Voltage
GND (Pin 1): Signal Ground. Tie to PGND under the
package.
LBO (Pin 2): Open-Collector Output of Comparator C3.
Can sink 100
µ
A. High impedance when device is in shut-
down.
SHDN (Pin 3): Shutdown. Pull high to shut down the
LT1305. Ground for normal operation.
FB (Pin 4): Feedback Input. Connects to main comparator
C1 input.
LBI (Pin 5): Low-Battery Comparator Input. When voltage
on this pin is below 1.24V, LBO is low.
V
IN
(Pin 6): Supply Pin. Must be bypassed with a large
value capacitor to gound. Keep bypass within 0.2" of the
device.
SW (Pin 7): Switch Pin. Connect inductor and diode here.
Keep layout short and direct to minimize radio frequency
interference.
PGND (Pin 8): Power Ground. Tie to signal ground (pin 1)
under the package. Bypass capacitor from V
IN
should be
tied directly to PGND within 0.2" of the device.
PI FU CTIO S
U
U
U
5
LT1305
BLOCK DIAGRA
M
W
+
+
+
6
7
8
3
2
5
1
4
+
+
C5
C4
L1
D1
V
IN
V
IN
R1
3
Q2
1
×
Q1
160
×
SHUTDOWN
LBO
LBI
GND
PGND
SW
R1
R2
C3
C2
C1
FB
OFF
OSCILLATOR
A3
DRIVER
CURRENT
COMPARATOR
HYSTERETIC
COMPARATOR
REFERENCE
1.24V
36mV
LT1305 · F01
Figure 1. LT1305 Block Diagram
OPERATIO
N
U
Operation of the LT1305 is best understood by referring to
the Block Diagram in Figure 1. When C1's negative input,
related to the output voltage by the appropriate resistor-
divider ratio, is higher than the 1.24V reference voltage,
C1's output is low. C2, A3 and the oscillator are turned off,
drawing no current. Only the reference and C1 consume
current, typically 120
µ
A. When C1's negative input drops
below 1.24V and overcomes C1's 6mV hysteresis, C1's
output goes high, enabling the oscillator, current compara-
tor C2 and driver A3. Quiescent current increases to 2mA
as the device goes into active switching mode. Q1 then
turns on in controlled saturation for nominally 6
µ
s or until
current comparator C2 trips, whichever comes first. The
switch then turns off for approximately 1.5
µ
s, then turns on
again. The LT1305's switching causes current to alter-
nately build up in L1 and dump into output capacitor C4 via
D1, increasing the output voltage. When the output is high
enough to cause C1's output to go high, switching action
ceases. Capacitor C4 is left to supply current to the load
until V
OUT
decreases enough to force C1's output high, and
the entire cycle repeats. Figure 2 details relevant wave-
forms. C1's cycling causes low-to-mid-frequency ripple
voltage on the output. Ripple can be reduced by making the
output capacitor large. The 220
µ
F unit specified results in
ripple of 50mV to 100mV on the 5V output. Paralleling two
capacitors will decrease ripple by approximately 50%.
V
OUT
100mV/DIV
AC COUPLED
V
SW
5V/DIV
I
L
1A/DIV
50
µ
s/DIV
LT1305 · F02
Figure 2. Burst Mode Operation
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