1
LT1949
600kHz, 1A Switch
PWM DC/DC Converter
VIN
VIN
3.3V
SW
FB
LT1949
L1
10µHD1
R2
140k
68k
330pF
VOUT
10V
175mA
R1
1M
1949 F01
C2
10µF
CERAMIC
C1
22µF
VCGND
SHDNSHUTDOWN
C1: AVX TAJA226M006R
C2: TAIYO YUDEN LMK325BJ106MN
D1: MBRM120LT3
L1: SUMIDA CDRH62B-100
+
The LT
®
1949 is a fixed frequency step-up DC/DC con-
verter with a 1A, 0.5Ω internal switch. Capable of gener-
ating 10V at 175mA from a 3.3V input, the LT1949 is ideal
for generating bias voltages for large screen LCD panels.
Constant frequency 600kHz operation results in a low
noise output that is easy to filter and the 30V switch rating
allows output voltage up to 28V using a single inductor. An
external compensation pin gives the user flexibility in
optimizing loop compensation, allowing small low ESR
ceramic capacitors to be used at the output. The 8-lead
MSOP and SO packages ensure a low profile overall
solution.
The LT1949 includes a low-battery detector that stays
alive when the device goes into shutdown. Quiescent
current in shutdown is 25µA, while operating current is
4.5mA.
■
1A, 0.5Ω, 30V Internal Switch
■
Operates with V
IN
as Low as 1.5V
■
600kHz Fixed Frequency Operation
■
Low-Battery Detector Stays Active in Shutdown
■
Low V
CESAT
Switch: 410mV at 800mA
■
Pin-for-Pin Compatible with the LT1317B
■
Small 8-Lead MSOP and SO Packages
■
LCD Bias Supplies
■
GPS Receivers
■
Battery Backup
■
Portable Electronic Equipment
■
Diagnostic Medical Instrumentation
, LTC and LT are registered trademarks of Linear Technology Corporation.
Figure 1. 3.3V to 10V/175mA DC/DC Converter Figure 2. 3.3V to 10V Converter Efficiency
LOAD CURRENT (mA)
90
80
70
60
50
40
30
20 5 10050 300
1949 F02
10
EFFICIENCY (%)
VOUT = 10V
3VIN
3.6VIN 4.2VIN
DESCRIPTIO
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FEATURES
APPLICATIO S
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TYPICAL APPLICATIO
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2
LT1949
V
IN
, LBO Voltage..................................................... 12V
SW Voltage ............................................... –0.4V to 30V
FB Voltage .................................................... V
IN
+ 0.3V
V
C
Voltage ................................................................ 2V
LBI Voltage ............................................ 0V ≤ V
LBI
≤ 1V
SHDN Voltage ........................................................... 6V
(Note 1)
LT1949EMS8
LTJC
Consult factory for Military grade parts.
1
2
3
4
V
C
FB
SHDN
GND
8
7
6
5
LBO
LBI
V
IN
SW
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C, θ
JA
= 120°C/W
Junction Temperature.......................................... 125°C
Operating Temperature Range (Note 2)
LT1949EMS8.......................................–40°C to 85°C
LT1949ES8/LT1949IS8 .......................–40°C to 85°C
Storage Temperature ........................... –65°C to 150°C
Lead Temperature (Soldering, 10sec).................. 300°C
ORDER PART
NUMBER
LT1949ES8
LT1949IS8
S8 PART MARKING
1949E
1949I
1
2
3
4
8
7
6
5
TOP VIEW
LBO
LBI
V
IN
SW
V
C
FB
SHDN
GND
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C, θ
JA
= 120°C/W
ORDER PART
NUMBER
MS8 PART MARKING
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VIN = 2V, VSHDN = 2V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
Quiescent Current ●4.5 7.5 mA
V
SHDN
= 0V ●25 40 µA
V
FB
Feedback Voltage 1.22 1.24 1.26 V
●1.20 1.24 1.26 V
I
B
FB Pin Bias Current (Note 3) ●12 80 nA
Input Voltage Range ●1.7 12 V
g
m
Error Amp Transconductance ∆I = 5µA●70 140 240 µmhos
A
V
Error Amp Voltage Gain 700 V/V
Maximum Duty Cycle ●80 85 %
Switch Current Limit (Note 4) V
IN
= 2.5V, Duty Cycle = 30% 1 1.13 1.5 A
V
IN
= 2.5V, Duty Cycle = 30% ●0.95 1.5 A
f
OSC
Switching Frequency ●500 600 750 kHz
Shutdown Pin Current V
SHDN
= V
IN
●0.015 0.1 µA
V
SHDN
= 0V ●–2.3 –7 µA
LBI Threshold Voltage 190 200 210 mV
●180 200 220 mV
LBO Output Low I
SINK
= 10µA●0.15 0.25 V
LBO Leakage Current V
LBI
= 250mV, V
LBO
= 5V ●0.02 0.1 µA
LBI Input Bias Current (Note 5) V
LBI
= 150mV ●560nA
Low-Battery Detector Gain 1MΩ Pull-Up 2000 V/V
Switch Leakage Current V
SW
= 5V ●0.01 3 µA
PACKAGE/ORDER I FOR ATIO
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W
ABSOLUTE AXI U RATI GS
WWWU
ELECTRICAL CHARACTERISTICS
3
LT1949
TYPICAL PERFOR A CE CHARACTERISTICS
UW
INPUT VOLTAGE
0
OSCILLATOR FREQUENCY (kHz)
700
650
600
550
500 2468
1949 G01
10 12
25°C
–40°C
85°C
Oscillator Frequency Switch Current Limit,
Duty Cycle = 30%
Switch Current Limit
TEMPERATURE (°C)
–50
SWITCH CURRENT (A)
1.3
1.2
1.1
1.0
0.9
0.8 –25 02550
1949 G03
75 100
Switch Voltage Drop (VCESAT)Feedback Voltage
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
1.25
1.24
1.23
1.22
1.21
1.20 –25 0 25 50
1949 G05
75 100
Quiescent Current, SHDN = 2V
TEMPERATURE (°C)
–50 –25
QUIESCENT CURRENT (mA)
1949 G06
4.6
4.5
4.4
4.3
4.2
4.1
4.0
3.9
3.8 0 255075100
SWITCH CURRENT (A)
0
SWITCH VOLTAGE (V)
1.0
0.8
0.6
0.4
0.2
00.2 0.4 0.6 0.8
1949 G04
1.0 1.2
85°C
–40°C
25°C
Note 3: Bias current flows into FB pin.
Note 4: Switch current limit guaranteed by design and/or correlation to
static tests. Duty cycle affects current limit due to ramp generator.
Note 5: Bias current flows out of LBI pin.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1949E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VIN = 2V, VSHDN = 2V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Switch V
CESAT
I
SW
= 800mA 410 mV
I
SW
= 500mA ●400 mV
Reference Line Regulation 1.8V ≤ V
IN
≤ 12V ●0.08 0.15 %/V
SHDN Input Voltage High ●1.4 6 V
SHDN Input Voltage Low ●0.4 V
ELECTRICAL CHARACTERISTICS
DUTY CYCLE (%)
0
SWITCH CURRENT (A)
1.3
1.2
1.1
1.0
0.9
0.8 80
1949 G02
20 40 60 100
4
LT1949
V
C
(Pin 1): Compensation Pin for Error Amplifier. Con-
nect a series RC network from this pin to ground. Typical
values for compensation are a 68k/330pF combination
when using ceramic output capacitors. Minimize trace
area at V
C
.
FB (Pin 2): Feedback Pin. Reference voltage is 1.24V.
Connect resistor divider tap here. Minimize trace area at
FB. Set V
OUT
according to: V
OUT
= 1.24V(1 + R1/R2).
SHDN (Pin 3): Shutdown. Pull this pin low for shutdown
mode (only the low-battery detector remains active).
Leave this pin floating or tie to a voltage between 1.4V and
6V to enable the device. SHDN pin is logic level and need
only meet the logic specification (1.4V for high, 0.4V for
low).
GND (Pin 4): Ground. Connect directly to local ground
plane.
SW (Pin 5): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to keep EMI down.
V
IN
(Pin 6): Supply Pin. Must be bypassed close to the
pin.
LBI (Pin 7):
Low-Battery Detector Input. 200mV refer-
ence. Voltage on LBI must stay between ground and
700mV. Low-battery detector remains active in shutdown
mode.
LBO (Pin 8): Low-Battery Detector Output. Open collec-
tor, can sink 10µA. A 1MΩ pull-up is recommended.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Load Regulation
VOUT
50mV/DIV
DC
COUPLED
OFFSET
ADDED
ILOAD 25mA/DIV
VIN = 3V
VOUT = 10V
L1 = 10µH, SUMIDA CD54
COUT = 10µF CERAMIC 1949 G10
Load Regulation
VOUT
50mV/DIV
DC
COUPLED
OFFSET
ADDED
ILOAD 50mA/DIV
VIN = 4V
VOUT = 10V
L1 = 10µH, SUMIDA CD54
COUT = 10µF CERAMIC 1949 G11
Transient Response
VOUT
100mV/DIV
AC COUPLED
50µs/DIV
VIN = 3.3V
VOUT = 10V
CIRCUIT OF FIGURE 1 1949 G12
IL
500mA/DIV
200mA
100mA
ILOAD
TEMPERATURE (°C)
–50
QUIESCENT CURRENT (µA)
26
25
24
23
22
21
20 –25 0 25 50
1317 TPC10
75 100
TEMPERATURE (°C)
–50 –25 0 25 50 75 100
FB PIN BIAS CURRENT (nA)
1317 TPC11
40
36
32
28
24
20
16
12
8
4
0
Quiescent Current, SHDN = 0V FB Pin Bias Current SHDN Pin Current
SHDN PIN VOLTAGE (V)
0
SHDN PIN CURRENT (µA)
35
1317 TPC12
12 4
2
1
0
–1
–2
–3 6
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PI FU CTIO S
5
LT1949
–
+
–
+
–
+
–
+
–
+
+
+
Σ
RAMP
GENERATOR
1.24V
REFERENCE
R
BIAS
V
C
g
m
FB
ENABLE
200mV
A = 2
FF
A1
COMPARATOR
A2
COMPARATOR
ERROR
AMPLIFIER
A4
0.06Ω
DRIVER
SW
GND
1949 BD
Q3
Q
S
600kHz
OSCILLATOR
5
LBO
LBI
SHDN
SHUTDOWN 3
7
1
4
R1
(EXTERNAL)
V
OUT
8
R2
(EXTERNAL)
FB
2
Figure 3. LT1949 Block Diagram
The LT1949 is a current mode, fixed frequency step-up
DC/DC converter with an internal 1A NPN power transis-
tor. Operation can best be understood by referring to the
Block Diagram.
At the beginning of each oscillator cycle, the flip-flop is set
and the switch is turned on. Current in the switch ramps
up until the voltage at A2’s positive input reaches the V
C
pin voltage, causing A2’s output to change state and the
switch to be turned off. The signal at A2’s positive input is
a summation of a signal representing switch current and
a ramp generator (introduced to avoid subharmonic oscil-
lations at duty factors greater than 50%). If the load
increases, V
OUT
(and FB) will drop slightly and the error
amplifier will drive V
C
to a higher voltage, causing current
in the switch to increase. In this way, the error amplifier
drives the V
C
pin to the voltage necessary to satisfy the
load. Frequency compensation is provided by an external
series RC network connected between the V
C
pin and
ground.
Layout Hints
The LT1949 switches current at high speed, mandating
careful attention to layout for proper performance.
You
will not get advertised performance with careless layouts.
Figure 4 shows recommended component placement for
a boost (step-up) converter. Follow this closely in your PC
layout. Note the direct path of the switching loops. Input
capacitor C1
must
be placed close (<5mm) to the IC
package. As little as 10mm of wire or PC trace from C
IN
to
V
IN
will cause problems such as inability to regulate or
oscillation.
The ground terminal of output capacitor C2 should tie
close to Pin 4 of the LT1949. Doing this reduces dI/dt in the
ground copper which keeps high frequency spikes to a
minimum. The DC/DC converter ground should tie to the
PC board ground plane at one place only, to avoid intro-
ducing dI/dt in the ground plane.
BLOCK DIAGRA
W
OPERATIO
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6
LT1949
APPLICATIONS INFORMATION
WUUU
Low-Battery Detector
The LT1949’s low-battery detector is a simple PNP input
gain stage with an open collector NPN output. The nega-
tive input of the gain stage is tied internally to a 200mV
±5% reference. The positive input is the LBI pin. Arrange-
ment as a low-battery detector is straightforward.
Figure␣ 5 details hookup. R1 and R2 need only be low
enough in value so that the bias current of the LBI pin
doesn’t cause large errors. For R2, 100k is adequate. The
200mV reference can also be accessed as shown in
Figure␣ 6. The low-battery detector remains active in
shutdown.
1
2
8
7
3
4
6
5
L1
C2
LBO
LBI
LT1949
V
OUT
V
IN
GND
SHUTDOWN
R1
R2
MULTIPLE
VIAs
GROUND PLANE
1949 F04
C1
+
Figure 4. Recommended Component Placement for Boost
Converter. Note Direct High Current Paths Using Wide PC
Traces. Minimize Trace Area at Pin 1 (VC) and Pin 2 (FB).
Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use
Vias at One Location Only to Avoid Introducing Switching
Currents into the Ground Plane
LBO
LBI
TO PROCESSOR
R1
1M
R2
100k
V
IN
LT1949
1949 F05
3.3V
GND
200mV
INTERNAL
REFERENCE
–
+
R1 = V
LB
– 200mV
2µA
Figure 5. Setting Low-Battery Detector Trip Point
V
IN
LT1949
LBI
LBO
200k
10µFGND
10k
1949 F06
2N3906
V
REF
200mV
+
Figure 6. Accessing 200mV Reference
OPERATIO
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7
LT1949
Dimensions in inches (millimeters) unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
PACKAGE DESCRIPTIO
MSOP (MS8) 1098
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.021 ± 0.006
(0.53 ± 0.015)
0° – 6° TYP
SEATING
PLANE
0.007
(0.18)
0.040 ± 0.006
(1.02 ± 0.15)
0.012
(0.30)
REF
0.006 ± 0.004
(0.15 ± 0.102)
0.034 ± 0.004
(0.86 ± 0.102)
0.0256
(0.65)
BSC 12
34
0.193 ± 0.006
(4.90 ± 0.15)
8765
0.118 ± 0.004*
(3.00 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
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 1298
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
1234
0.150 – 0.157**
(3.810 – 3.988)
8765
0.189 – 0.197*
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
V
IN
V
IN
4V TO 9V
SW
FB
LT1949
L1
10µH
L2
10µH
D1
33k
1M
3.3nF
C2
4.7µF
16V V
OUT
5V
250mA
1949 TA02
C3
10µF
6.3V
C1
4.7µF
16V V
C
GND
SHDN
C1, C2: TAIYO YUDEN EMK316BJ475ML
C3: TAIYO YUDEN JMK316BJ106ML
D1: MOTOROLA MBRM120LT3
L1, L2: SUMIDA CR32-100KC
1M
1M
1%
332k
1%
4 Cell to 5V SEPIC Converter
TYPICAL APPLICATIO
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8
LT1949
LINEAR TECHNOLOGY CORPORATION 1999
1949f LT/TP 0300 4K • PRINTED IN THE USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
PART NUMBER DESCRIPTION COMMENTS
LT1054 High Power Regulated Charge Pump Up to 100mA Output with No Inductors
LT1302 High Output Current Micropower DC/DC Converter 5V/600mA from 2V, 2A Internal Switch, 200µA I
Q
LT1304 2-Cell Micropower DC/DC Converter Low-Battery Detector Active in Shutdown
LT1307B Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from 1 Cell, MSOP Package
LT1308B 2A 600kHz PWM DC/DC Converter TSSOP Package
LT1317B Micropower, 600kHz PWM DC/DC Converter 2 Cells to 3.3V at 200mA, MSOP Package
LTC®1516 2-Cell to 5V Regulated Charge Pump 12µA I
Q
, No Inductors, 5V at 50mA from 3V Input
LT1613 Single Cell 1.4MHz PWM DC/DC Converter 3.3V to 5V at 200mA, SOT-23 Package
LTC1682 Doubler Charge Pump with Low Noise Linear Regulator 3.3V and 5V Outputs with 60µV
RMS
Noise, Up to 80mA Output
LTC1754 Micropower 3.3V/5V Charge Pump with Shutdown Up to 50mA Output, I
Q
= 13µA, SOT-23 Package
RELATED PARTS
V
IN
V
IN
3.3V
SW
FB
LT1949
L1
10µHD7
R3
7.5k
1%
R2
40.2k
1%
R1
47k
1949 TA01
C2
10µF
C7
0.1µFC8
0.1µFC9
0.1µF
C4
4.7µF
C5
4.7µF
C1
22µF
C3
680pF
D5
D1 D2
–8V
10mA
8V
200mA
23V
5mA
D6
C6
4.7µF
V
C
GND
SHDNSHUTDOWN
LBI
LB0
C1: AVX TAJB226M010
C2: TAIYO YUDEN TMK432BJ106MN X7R 1210
C4, C5, C6: TAIYO YUDEN LMK316BJ475ML X5R1206
C7, C8, C9: 0.1µF CERAMIC, 50V
D1 TO D6: FMMD7000, DUAL DIODE
D7: MBRM120LT3
L1: SUMIDA CDRH62B-100
+
D3 D4
Low Profile Triple Output LCD Bias Generator
TYPICAL APPLICATIO
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