LT1305CS8 [Linear]
Micropower High Power DC/DC Converter with Low-Battery Detector; 微高功率DC / DC转换器与低电池电压检测器
| 型号： | LT1305CS8 |
| 厂家： | 
Linear |
| 描述： | Micropower High Power DC/DC Converter with Low-Battery Detector |
| 文件： | 总8页 (文件大小：238K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1305
Micropower High Power
DC/DC Converter with
Low-Battery Detector
U
DESCRIPTIO
EATURE
S
F
The LT®1305 is a micropower step-up DC/DC converter
that uses Burst ModeTM 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.
■
■
■
■
■
■
■
5V at 400mA from 2V Input
Supply Voltage As Low As 1.8V
120µA Quiescent Current
Low-Battery Detector
Low VCESAT Switch: 310mV at 2A Typ
Uses Inexpensive Surface Mount Inductors
8-Lead SO Package
Quiescent current is only 120µA and the Shutdown pin
further reduces current to 10µA. A low-battery detector
provides an open-collector output that goes low when the
input voltage drops below a preset level. The LT1305 is
availableinan8-pinSO,easingboardspacerequirements.
O U
PPLICATI
S
A
■
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation
2-Cell and 3-Cell to 5V Conversion
EL Panel Drivers
Portable Instruments
U
O
TYPICAL APPLICATI
2-Cell and 3-Cell to 5V/400mA DC/DC Converter
with Low-Battery Detect
Efficiency
90
L1
D1
10µH
V
V
= 4.00V
= 3.00V
IN
LOW BATTERY
GOES LOW AT
BAT
316k
1%
V
LBI
SW
LBO
IN
IN
100k
V
= 2.2V
80
70
60
+
412k
1%
C1
220µF
301k
1%
2 TO 3
CELLS
LT1305
V
V
= 2.00V
= 2.50V
V
IN
OUT
SHDN
GND
5V
400mA
SHUTDOWN
FB
PGND
IN
+
C2
220µF
100k
1%
C1, C2: AVX TPSE227010R0100
D1: MOTOROLA MBRS130LT3
L1: COILCRAFT D03316-103
LT1305 • TA03
1
10
100
1000
LOAD CURRENT (mA)
LT1305 • TA02
1
LT1305
W W W
U
ABSOLUTE AXI U RATI GS
/O
PACKAGE RDER I FOR ATIO
VIN 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
TOP VIEW
NUMBER
GND
LBO
1
2
3
4
8
7
6
5
PGND
SW
LT1305CS8
SHDN
FB
V
IN
LBI
S8 PART MARKING
1305
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 100°C, θJA = 80°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
TA = 25°C, VIN = 2.0V, unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Quiescent Current
V
SHDN
V
SHDN
= 0.5V, V = 2V
= 1.8V
●
●
120
7
200
15
µA
µA
Q
FB
V
Input Voltage Range
1.8
2.0
1.55
V
V
IN
●
●
●
●
Feedback Voltage
1.22
1.24
6
1.26
12.5
20
V
mV
nA
Comparator Hysteresis
Feedback Pin Bias Current
Oscillator Frequency
Oscillator TC
V
= 1V
7
FB
Current Limit Not Asserted
120
75
155
0.2
86
185
kHz
%/°C
%
DC
Maximum Duty Cycle
Switch On Time
●
95
t
Current Limit Not Asserted
5.6
0.06
140
0.1
2
µs
ON
Output Line Regulation
Switch Saturation Voltage
Switch Leakage Current
Peak Switch Current
1.8V < V < 6V
●
●
●
0.15
280
10
%/V
mV
µA
IN
V
CESAT
I
= 1A
SW
V
V
= 5V, Switch Off
SW
= 2V
1.35
1.20
2.35
2.50
A
A
IN
●
V
= 5V
1.15
1.21
2.15
1.27
20
A
V
IN
LBI Trip Voltage
(Note 2)
= 1V
●
●
●
●
●
1.24
7
LBI Input Bias Current
LBO Output Low
V
LBI
nA
V
I
= 100µA
0.11
0.1
0.4
5
LOAD
LBO Leakage Current
Shutdown Pin High
Shutdown Pin Low
Shutdown Pin Bias Current
V
LBI
= 1.3V, V
= 5V
LBO
µA
V
V
V
1.8
SHDNH
SHDNL
SHDN
0.5
20
V
I
V
SHDN
V
SHDN
V
SHDN
= 5V
= 2V
= 0V
●
●
●
8.0
3.0
0.1
µA
µA
µA
1
The
●
denotes specifications which apply over the 0°C to 70°C operating
Note 2: Low-battery detector comparator is inoperative when device is in
shutdown.
temperature range.
Note 1: Hysteresis specified is DC. Output ripple may be higher if output
capacitance is insufficient or capacitor ESR is excessive.
2
LT1305
W
U
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Duty Cycle
Switch On Time
Oscillator Frequency
8
7
6
5
4
3
2
200
190
100
95
180
170
160
90
85
80
150
140
75
70
130
120
110
100
65
60
55
50
–50
0
25
50
75
100
–25
–50 –25
25
50
75
100
–50 –25
25
50
75
100
0
0
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
LT1305 • G01
LT1305 • G02
LT1305 • G03
Current Limit
Quiescent Current
Quiescent Current
500
400
300
200
100
0
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
200
190
SWITCH OFF
T = 25°C
A
SWITCH OFF
V
= 2V
IN
180
170
160
150
140
130
120
110
100
50
TEMPERATURE (˚C)
100
0
2
4
6
8
10
–50 –25
0
25
75
–50 –25
25
50
75
100
0
INPUT VOLTAGE (V)
TEMPERATURE (°C)
LT1305 • G05
LT1305 • G06
LT1305 • G04
LBI Pin Bias Current
FB Pin Bias Current
FB Voltage
20
18
20
18
1.250
1.245
16
14
12
16
14
12
1.240
1.235
1.230
10
8
10
8
1.225
1.220
6
4
2
0
6
4
2
0
1.215
1.210
1.205
1.200
–50 –25
25
50
75
100
–50 –25
25
50
75
100
–50 –25
25
50
75
100
0
0
0
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
LT1305 • G07
LT1305 • G08
LT1305 • G09
3
LT1305
TYPICAL PERFORMANCE CHARACTERISTICS
W
U
Low-Battery Detect Trip Point
Switch Saturation Voltage
Switch Saturation Voltage
400
350
300
250
200
150
100
50
300
250
200
150
100
50
1.250
1.245
T
= 25°C
I
= 1A
A
SW
1.240
1.235
1.230
1.225
1.220
1.215
1.210
1.205
1.200
0
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SWITCH CURRENT (A)
–50
0
25
50
75
100
–25
–50 –25
25
50
75
100
0
TEMPERATURE (°C)
TEMPERATURE (°C)
LT1305 • F12
LT1305 • G13
LT1305 • G10
U
U
U
PI FU CTIO S
GND (Pin 1): Signal Ground. Tie to PGND under the
package.
LBI (Pin 5): Low-Battery Comparator Input. When voltage
on this pin is below 1.24V, LBO is low.
LBO (Pin 2): Open-Collector Output of Comparator C3.
Can sink 100µA. High impedance when device is in shut-
down.
VIN (Pin 6): Supply Pin. Must be bypassed with a large
value capacitor to gound. Keep bypass within 0.2" of the
device.
SHDN (Pin 3): Shutdown. Pull high to shut down the
SW (Pin 7): Switch Pin. Connect inductor and diode here.
Keep layout short and direct to minimize radio frequency
interference.
LT1305. Ground for normal operation.
FB (Pin 4): Feedback Input. Connects to main comparator
C1 input.
PGND (Pin 8): Power Ground. Tie to signal ground (pin 1)
under the package. Bypass capacitor from VIN should be
tied directly to PGND within 0.2" of the device.
4
LT1305
W
BLOCK DIAGRAM
D1
L1
V
IN
+
+
V
IN
SW
C5
C4
6
7
36mV
CURRENT
COMPARATOR
+
–
R1
C2
3Ω
R1
R2
HYSTERETIC
COMPARATOR
OFF
FB
4
–
Q2
1×
Q1
160×
A3
DRIVER
OSCILLATOR
C1
REFERENCE
1.24V
+
–
C3
+
SHUTDOWN
3
GND
1
LBI
LBO
PGND
5
2
8
LT1305 • F01
Figure 1. LT1305 Block Diagram
U
OPERATION
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 120µA. When C1’s negative input drops
below 1.24V and overcomes C1’s 6mV hysteresis, C1’s
outputgoeshigh,enablingtheoscillator,currentcompara-
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 6µs or until
current comparator C2 trips, whichever comes first. The
switchthenturnsoffforapproximately1.5µs,thenturnson
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
untilVOUT decreasesenoughtoforceC1’soutputhigh, and
the entire cycle repeats. Figure 2 details relevant wave-
forms. C1’s cycling causes low-to-mid-frequency ripple
voltageontheoutput. Ripplecanbereducedbymakingthe
output capacitor large. The 220µF unit specified results in
ripple of 50mV to 100mV on the 5V output. Paralleling two
capacitors will decrease ripple by approximately 50%.
VOUT
100mV/DIV
AC COUPLED
VSW
5V/DIV
IL
1A/DIV
LT1305 • F02
50µs/DIV
Figure 2. Burst Mode Operation
5
LT1305
U
OPERATION
Inductor Selection
If switch current reaches 2A, causing C2 to trip, switch on
time is reduced and off time increases slightly. This allows
continuous operation during bursts. C2 monitors the
voltage across 3Ω resistor R1 which is directly related to
the switch 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 36mV, corresponding to 2A
switch current, C2’s output goes high, truncating the on
time portion of the oscillator cycle and increasing off time
to about 2µs. Response time of C2, which determines
minimum on time, is approximately 300ns.
Inductors used with the LT1305 must fulfill two require-
ments. First, the inductor must be able to handle current
of 2A to 2.5A without runaway saturation. Rod or drum
coreunitsusuallysaturategraduallyanditisacceptableto
exceed manufacturer’s published saturation current by
20% or so. Second, the unit must have low DCR, under
0.05Ω so that copper loss is kept low and excess heating
is avoided. Inductance value is not critical. Generally, for
low voltage inputs below 3V a 10µH inductor is recom-
mended(suchasCoilcraftDO3316-103).Forinputsabove
4V to 5V use a 22µH unit (such as Coilcraft DO3316-223).
Switching frequency can reach up to 300kHz so the core
material should be able to operate at high frequency
without excessive core loss. Ferrite or molypermalloy
cores are a better choice than powdered iron. If EMI is a
concern, a toroidal inductor is suggested, such as
Coiltronics CTX20-4.
Low-Battery Detector
Thelow-batterydetectorisenabledwhenSHDNislowand
disabled when SHDN is high. The comparator has no
hysteresis built in, but hysteresis can be added by
connecting a high-value resistor from LBI to LBO as
shown in Figure 3. The internal reference can be accessed
via the comparator as shown in Figure 4.
Capacitor Selection
5V
V
BAT
LT1305
Output and input capacitors should have low ESR for best
performance. Inexpensive aluminum electrolytics some-
times have ESR above 1Ω, even for relatively large values
such as 100µF, 16V units. Since the LT1305 has a 2A
current limit, 2V of ripple voltage would result with such a
capacitorattheoutput. KeepESRbelow0.05Ωto0.1Ωfor
reasonable ripple voltage. Tantalum capacitors such as
AVX TPS series or Sprague 593D have low ESR and are
surface mount components. For lowest ESR, use Sanyo
OS-CON units (OS-CON is also available from Vishay).
These capacitors have superior ESR, small size and per-
form well at cold temperatures.
R4
47k
R1
1.24V
LBI
–
+
LBO
R2
49.9k
1%
R3
2M
R1 = (V
HYSTERESIS ≈ 30mV
–1.24V) (43.5k)
TRIP
LT1305 • F03
Figure 3. R3 Adds Hysteresis to Low-Battery Detector
V
IN
Diode Selection
100k
V
IN
LBO
2N3906
A 2A Schottky diode such as Motorola MBRS130LT3 is a
good choice for the rectifier diode. A 1N5821 or
MBRS130T3 are suitable as well. Do not use “general
purpose”diodessuchas1N4001. Theyaremuchtooslow
for use in switching regulator applications.
LT1305
R2
V
REF
LBI
OUTPUT
+
GND
R1
2.2µF
R2
V
V
= 1.24V 1 +
REF
(
)
R1
≥ V
REF
R1 + R2 ≈ 33k
+ 200mV
IN
LT1305 • F04
Figure 4. Accessing Internal Reference
6
LT1305
U
TYPICAL APPLICATIONS N
Setting Output Voltage
4-Cell-to-5V Converter
L1*
100µF**
MBRS130LT3
1N5817
L1
+
22µH
3.5V to 6.5V
4 CELLS
V
IN
V
SW
V
IN
SW
IN
5V
+
V
OUT
400mA
100µF
+
R2
R1
LT1305
309k
100k
LT1305
100µF
+
+
SHDN
GND
220µF
FB
PGND
FB
PGND
22µH*
150µF**
GND
SHUTDOWN
*COILCRAFT DO3316-223 OR
SUMIDA CD105-220
**SANYO OS-CON
LT1305 • TA05
LT1305 • TA03
R2
R1
V
OUT
= 1.24V 1 +
(
)
5V Step-Up Converter with Reference Output
MBRS130LT3
10µH*
1.8V TO 4.5V
INPUT
100k
V
SW
IN
5V
400mA
LBO
2N3906
+
LT1305
309k
100k
100µF
V
REF
+
OUTPUT
1.24V
LBI
GND
FB
PGND
220µF
+
2.2µF
33k
*COILCRAFT DO3316-103
LT1305 • TA06
EL Panel Driver
T1**
1:15
MUR160
V
IN
•
1.5V TO 8V
4, 5
6
C1*
50pF
10
10Ω
•
1, 2
1N5818
4.7µF
160V
+
3.3M
V
SW
EL PANEL
IN
+
3.3M
3.3M
1k
47µF††
1/2W
0.1µF
CERAMIC
LT1305
1N4148
10k
ZETEX
FZT658
SHDN
GND
FB
PGND
C
≤ 100nF
PANEL
51k
SHUTDOWN
R1†
25k
LT1305 • TA04
100Hz TO 1000Hz
SQUARE WAVE
DRIVE
*ADD C1 FOR OPEN-PANEL PROTECTION
**DALE LPE5047-A132 1:15 TURNS RATIO
10µH PRIMARY INDUCTANCE (605) 666-9301
†R1 ADJUSTS V
83V TO 115V
OUT
RMS
RMS
††AVX TPS OR SANYO OS-CON MUST HAVE ESR ≤0.15Ω
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
7
LT1305
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic SOIC
0.189 – 0.197*
(4.801 – 5.004)
7
5
8
6
0.150 – 0.157*
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
3
4
2
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
SO8 0294
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
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LT/GP 0595 10K • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
8
●
●
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LINEAR TECHNOLOGY CORPORATION 1995
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