LT1304/LT1304-3.3/LT1304-5
Micropower
DC/DC Converters with
Low-Battery Detector
Active in Shutdown
FEATURES
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DESCRIPTION
The LT
®
1304 is a micropower step-up DC/DC converter
ideal for use in small, low voltage, battery-operated sys-
tems. The devices operate from a wide input supply range
of 1.5V to 8V. The LT1304-3.3 and LT1304-5 generate
regulated outputs of 3.3V and 5V and the adjustable
LT1304 can deliver output voltages up to 25V. Quiescent
current, 120µA in active mode, decreases to just 10µA in
shutdown with the low-battery detector still active. Peak
switch current, internally set at 1A, can be reduced by
adding a single resistor from the I
LIM
pin to ground. The
high speed operation of the LT1304 allows the use of
small, surface-mountable inductors and capacitors. The
LT1304 is available in an 8-lead SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
5V at 200mA from Two Cells
10µA Quiescent Current in Shutdown
Operates with V
IN
as Low as 1.5V
Low-Battery Detector Active in Shutdown
Low Switch V
CESAT
: 370mV at 1A Typical
120µA Quiescent Current in Active Mode
Switching Frequency Up to 300kHz
Programmable Peak Current with One Resistor
8-Lead SO Package
APPLICATIONS
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2-, 3-, or 4-Cell to 5V or 3.3V Step-Up
Portable Instruments
Bar Code Scanners
Palmtop Computers
Diagnostic Medical Instrumentation
Personal Data Communicators/Computers
TYPICAL APPLICATION
2-Cell to 5V Step-Up Converter with Low-Battery Detect
22µH*
3
V
IN
LBI
4
SW
SENSE
LT1304-5
6
I
LIM
SHDN
7
SHUTDOWN
*SUMIDA CD54-220
**1N5817
1304 TA01
D1**
90
499k
1
8
100k
2 CELLS
100µF
604k
NC
100µF
LBO
LOW WHEN
V
BAT
< 2.2V
EFFICIENCY (%)
+
+
5V
200mA
80
70
LBO
GND
5
2
60
V
IN
= 3.3V
V
IN
= 2.5V
V
IN
= 1.8V
1
10
100
LOAD CURRENT (mA)
500
1304 TA02
50
40
0.1
U
U
U
Efficiency
1
LT1304/LT1304-3.3/LT1304-5
ABSOLUTE
MAXIMUM
RATINGS
V
IN
Voltage ................................................................ 8V
SW Voltage ............................................... – 0.4V to 25V
FB Voltage (LT1304) ...................................... V
IN
+ 0.3V
Sense Voltage (LT1304-3.3/LT1304-5) ..................... 8V
I
LIM
Voltage .............................................................. 5V
SHDN Voltage ............................................................ 6V
LBI Voltage ............................................................... V
IN
LBO Voltage ............................................................... 8V
Maximum Power Dissipation ............................. 500mW
Junction Temperature.......................................... 125°C
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
ORDER PART
NUMBER
TOP VIEW
LBI 1
LBO 2
V
IN
3
SW 4
8
7
6
5
FB (SENSE)*
SHDN
I
LIM
GND
LT1304CS8
LT1304CS8-3.3
LT1304CS8-5
S8 PART MARKING
1304
13043
13045
S8 PACKAGE
8-LEAD PLASTIC SO
*FIXED OUTPUT VERSION
T
JMAX
= 125°C,
θ
JA
= 150°C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating Voltage
Operating Voltage Range
Quiescent Current
Quiescent Current in Shutdown
Comparator Trip Point
FB Pin Bias Current
Sense Pin Leakage in Shutdown
Output Sense Voltage
Line Regulation
LBI Input Threshold
LBI Bias Current
LBI Input Hysteresis
LBO Output Voltage Low
LBO Output Leakage Current
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Pin Bias Current
Switch OFF Time
Switch ON Time
Maximum Duty Cycle
Peak Switch Current
V
SHDN
= 5V
V
SHDN
= 0V
I
SINK
= 500µA
CONDITIONS
V
IN
= 2V, V
SHDN
= 2V unless otherwise noted.
MIN
q
q
TYP
1.5
120
7
27
MAX
1.65
8
200
15
50
1.26
25
1
3.43
5.25
0.15
1.25
20
65
0.4
0.1
0.4
UNITS
V
V
µA
µA
µA
V
nA
µA
V
V
%/V
V
nA
mV
V
µA
V
V
µA
µA
µs
µs
%
A
mA
V
SHDN
= 2V, Not Switching
V
SHDN
= 0V, V
IN
= 2V
V
SHDN
= 0V, V
IN
= 5V
LT1304
LT1304
V
SHDN
= 0V, Fixed Output Versions
LT1304-3.3
LT1304-5
1.8V
≤
V
IN
≤
8V
Falling Edge
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
1.22
1.24
10
0.002
3.17
4.80
1.10
3.3
5.05
0.04
1.17
6
35
0.2
0.01
LBI = 1.5V, LBO = 5V
1.4
5
–2
1.5
6
80
1
500
8
2
8
88
1.2
–5
1
4
76
0.8
Current Limit Not Asserted
Current Limit Not Asserted
I
LIM
Pin Open, V
IN
= 5V
20k from I
LIM
to GND
q
q
2
U
W
U
U
W W
W
LT1304/LT1304-3.3/LT1304-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Switch Saturation Voltage
Switch Leakage
CONDITIONS
I
SW
= 1A
I
SW
= 700mA
V
IN
= 2V, V
SHDN
= 2V unless otherwise noted.
MIN
q
q
TYP
0.37
0.26
0.01
MAX
0.35
7
UNITS
V
V
µA
Switch Off, V
SW
= 5V
The
q
denotes specifications which apply over the 0°C to 70°C operating
temperature range.
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
500
T
A
= 25°C
1.2
SATURATION VOLTAGE (mV)
400
PEAK CURRENT (A)
1.0
0.9
0.8
0.7
TIME (µs)
300
200
100
0
0
0.2
0.4
0.6
0.8
SWITCH CURRENT (A)
1.0
1.2
1304 G01
Feedback Voltage
1.250
1.245
1.240
FEEDBACK VOLTAGE (V)
BIAS CURRENT (nA)
1.235
1.230
1.225
1.220
1.215
1.210
1.205
1.200
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
20
18
14
12
10
8
6
4
2
0
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
1304 G05
SUPPLY CURRENT (µA)
U W
1304 G04
Peak Switch Current Limit
1.3
8
7
6
5
4
3
2
1
–25
0
25
50
TEMPERATURE (°C)
75
100
1304 G02
On- and Off-Times
MAXIMUM ON-TIME
1.1
OFF-TIME
0.6
–50
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1304 G03
Feedback Pin Bias Current
300
Supply Current
T
A
= 25°C
250
200
150
100
50
0
V
SHDN
= V
IN
NOT SWITCHING
16
V
SHDN
= 0V
0
1
2
6
4
3
5
INPUT VOLTAGE (V)
7
8
1304 G06
3
LT1304/LT1304-3.3/LT1304-5
TYPICAL PERFORMANCE CHARACTERISTICS
Load Transient Response
V
OUT
100mV/DIV
AC COUPLED
I
LOAD
200mA
0
100µs/DIV
1304 G07
PIN FUNCTIONS
LBI (Pin 1):
Low-Battery Detector Input. When voltage on
this pin is less than 1.17V, detector output is low.
LBO (Pin 2):
Low-Battery Detector Output. Open collector
can sink up to 500µA. Low-battery detector remains active
when device is shut down.
V
IN
(Pin 3):
Input Supply. Must be bypassed close (< 0.2")
to the pin. See required layout in the Typical Applications.
SW (Pin 4):
Collector of Power NPN. Keep copper traces on
this pin short and direct to minimize RFI.
GND (Pin 5):
Device Ground. Must be low impedance;
solder directly to ground plane.
I
LIM
(Pin 6):
Current Limit Set Pin. Float for 1A peak switch
current; a resistor to ground will lower peak current.
SHDN (Pin 7):
Shutdown Input. When low, switching
regulator is turned off. The low-battery detector remains
active. The SHDN input should not be left floating. If SHDN
is not used, tie the pin to V
IN
.
FB/SENSE (Pin 8):
On the LT1304 (adjustable) this pin
goes to the comparator input. On the fixed-output ver-
sions, the pin connects to the resistor divider which sets
output voltage. The divider is disconnected from the pin
during shutdown.
4
U W
Burst Mode
TM
Operation
V
OUT
100mV/DIV
AC COUPLED
V
SW
5V/DIV
I
L
500mA/DIV
V
IN
= 2.5V
V
OUT
= 5V
I
LOAD
= 185mA
L = 22µH
20µs/DIV
1304 G08
Burst Mode is a trademark of Linear Technology Corporation.
U
U
U
LT1304/LT1304-3.3/LT1304-5
BLOCK DIAGRA S
V
IN
1
R3
8
R4
FB
Figure 1. LT1304 Block Diagram. Independent Low-Battery Detector A3 Remains Alive When Device Is in Shutdown
8
SENSE
R1 = 355k (LT1304-3.3), 195k (LT1304-5)
W
LBI
+
C1
3
L1
V
IN
SW
D1
4
+
V
OUT
C2
2
LB0
1.5V
UNDERVOLTAGE
LOCKOUT
36mV
+
A2
+
A3
BIAS
~1V
–
1.17V
–
Q3
R2
1k
R1
7.2Ω
OFF
–
A1
ENABLE
+
1.24V
V
REF
TIMERS
6µs ON
1.5µs OFF
DRIVER
1k
Q2
×1
Q1
×200
SHUTDOWN
7
SHDN
6
I
LIM
5
GND
1304 F01
LBI
1
LB0
2
1.5V
UNDERVOLTAGE
LOCKOUT
36mV
V
IN
3
SW
4
+
A2
+
A3
BIAS
~1V
–
1.17V
590k
–
Q3
R2
1k
R1
7.2Ω
OFF
–
R1
A1
ENABLE
+
1.24V
V
REF
TIMERS
6µs ON
1.5µs OFF
DRIVER
1k
Q2
×1
Q1
×200
SHUTDOWN
SHDN
7
6
I
LIM
5
GND
1304 F02
Figure 2. LT1304-3.3/LT1304-5 Block Diagram
5
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