LT3494/LT3494A
Micropower Low Noise
Boost Converters with
Output Disconnect
FEATURES
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DESCRIPTION
The LT
®
3494/LT3494A are low noise boost converters
with integrated power switch, Schottky diode and output
disconnect circuitry. The parts use a novel* control tech-
nique resulting in low output voltage ripple as well as high
efficiency over a wide load current range. This technique
guarantees that the switching frequency stays above the
audio band for the entire load range. The parts feature a high
performance NPN power switch with a 350mA and 180mA
current limit for the LT3494A and LT3494 respectively. The
quiescent current is a low 65μA, which is further reduced
to less than 1μA in shutdown. The internal disconnect
circuitry allows the output voltage to be isolated from the
input during shutdown. An auxiliary reference input (CTRL
pin) overrides the internal 1.225V feedback reference with
any lower value allowing full control of the output voltage
during operation. The LT3494/LT3494A are available in a
tiny 8-lead 3mm
×
2mm DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Patent pending.
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Low Quiescent Current
65μA in Active Mode
1μA in Shutdown Mode
Switching Frequency is Non-Audible Over Entire
Load Range
Integrated Power NPN:
350mA Current Limit (LT3494A)
180mA Current Limit (LT3494)
Integrated Schottky Diode
Integrated Output Disconnect
Integrated Output Dimming
Wide Input Range: 2.3V to 16V
Wide Output Range: Up to 40V
Tiny 8-Lead 3mm
×
2mm DFN Package
APPLICATIONS
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OLED Power
Low Noise Power
MP3 Players
TYPICAL APPLICATION
OLED Power Supply from One Li-Ion Cell
V
IN
3V
TO 4.2V
15μH
4.7μF
SW
V
CC
SHDN
CTRL
CAP
V
OUT
2.21M
FB
GND
3494 TA01a
Output Voltage Ripple
vs Load Current
15
V
OUT
PEAK-TO-PEAK RIPPLE (mV)
LT3494
FIGURE 5 CIRCUIT
100MHz MEASUREMENT BW
EFFICIENCY (%)
90
80
70
60
50
40
30
0
0.1
1
10
LOAD CURRENT (mA)
100
3494 TA01b
Efficiency and Power Loss
vs Load Current
V
IN
= 3.6V
280
LOAD FROM
CAPACITOR
LOAD FROM
V
OUT
240
200
160
120
80
40
0
100
3494 TA01c
POWER LOSS (mW)
0.22μF
V
OUT
16V
16mA
2.2μF
10
LT3494
5
20
0.1
1
10
LOAD CURRENT (mA)
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LT3494/LT3494A
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
SW 1
GND 2
V
CC
3
CTRL 4
9
8
7
6
5
CAP
V
OUT
FB
SHDN
V
CC
Voltage ...............................................................16V
SW Voltage ...............................................................40V
CAP Voltage ..............................................................40V
V
OUT
Voltage .............................................................40V
SHDN Voltage ...........................................................16V
CTRL Voltage ............................................................16V
FB Voltage ................................................................2.5V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
DDB PACKAGE
8-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3494EDDB
LT3494AEDDB
DDB PART MARKING
LCCD
LCRW
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating Voltage
Maximum Operating Voltage
Feedback Voltage
FB Resistor
Quiescent Current
Quiescent Current in Shutdown
Minimum Switch Off Time
Maximum Switch Off Time
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Schottky Forward Voltage
Schottky Reverse Leakage
PMOS Disconnect V
CAP
– V
OUT
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Pin Bias Current
V
SHDN
= 3V
V
SHDN
= 0V
CONDITIONS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 3V, V
SHDN
= V
CC
, unless otherwise noted. (Note 2)
MIN
TYP
2.3
V
CTRL
= 3V (Note 3)
Not Switching
V
⎯
S
⎯
H
⎯
D
⎯
N
= 0V, V
CC
= 3V
After Start-Up Mode, V
FB
= 1V, V
CTRL
= 3V (Note 4)
During Start-Up Mode, V
FB
= 0.2V, V
CTRL
= 3V (Note 4)
V
FB
= 1.5V
LT3494A (Note 5)
LT3494 (Note 5)
LT3494A, I
SW
= 200mA
LT3494, I
SW
= 100mA
V
SW
= 5V, V
⎯
S
⎯
H
⎯
D
⎯
N
= 0
I
DIODE
= 100mA
I
OUT
= 10mA, V
CAP
= 5V
1.5
0.3
5
0
10
0.1
●
●
●
MAX
2.5
16
1.245
184
75
1
UNITS
V
V
V
kΩ
μA
μA
ns
ns
1.205
179
1.225
182
65
0
100
450
15
225
115
20
350
180
180
110
0.01
900
0.05
250
30
450
250
μs
mA
mA
mV
mV
1
1100
1
μA
mV
μA
mV
V
V
μA
μA
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LT3494/LT3494A
ELECTRICAL CHARACTERISTICS
PARAMETER
CTRL Pin Bias Current
CTRL to FB Offset
Maximum Shunt Current
CONDITIONS
V
CTRL
= 0.5V, Current Flows Out of Pin
V
CTRL
= 0.5V
V
FB
= 1.3V, V
CAP
= 5V
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 3V, V
SHDN
= V
CC
, unless otherwise noted. (Note 2)
MIN
TYP
20
8
230
MAX
100
15
UNITS
nA
mV
μA
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT3494/LT3494A are guaranteed to meet performance
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
Internal reference voltage is determined by finding V
FB
voltage
level which causes quiescent current to increase 20μA above “Not
Switching” level.
Note 4:
If CTRL is overriding the internal reference, Start-Up mode occurs
when V
FB
is less then half the voltage on CTRL. If CTRL is not overriding
the internal reference, Start-Up mode occurs when V
FB
is less then half the
voltage of the internal reference.
Note 5:
Current limit guaranteed by design and/or correlation to static test.
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
vs Load Currrent
1400
LT3494
FIGURE 5 CIRCUIT
1200 V
CC
= 3.6V
V
OUT
= 16V
1000
800
600
400
200
0
0.1
2.0
T
A
= 25°C unless otherwise noted.
Load Regulation
LT3494
1.5 FIGURE 5 CIRCUIT
V
CC
= 3.6V
1.0 V
OUT
= 16V
0.5
0
–0.5
–1.0
–1.5
–2.0
V
OUT
VOLTAGE (V)
0
5
10 15 20 25 30
LOAD CURRENT (mA)
35
40
20
V
OUT
vs CTRL Voltage
LT3494
FIGURE 5 CIRCUIT
V
CC
= 3.6V
15 V
OUT
= 16V
LOAD CURRENT = 1mA
SWITCHING FREQUENCY (kHz)
V
OUT
VOLTAGE CHANGE (%)
10
5
0
0.1
0.3
0.5 0.7 0.9 1.1
CTRL VOLTAGE (V)
1.3
1.5
1
10
LOAD CURRENT (mA)
100
3494 G01
3494 G02
3494 G03
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LT3494/LT3494A
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Temperature
2.0
OUTPUT VOLTAGE CHANGE (%)
LT3494
1.5 FIGURE 5 CIRCUIT
SWITCHING FREQUENCY (kHz)
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3494 G04
T
A
= 25°C unless otherwise noted.
Quiescent Current–Not Switching
100
95
90
Minimum Switching Frequency
51.0
50.5
50.0
I
VCC
(μA)
49.5
49.0
48.5
48.0
47.5
47.0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3494 G05
V
CC
= 3.6V
NO LOAD
85
80
75
70
65
60
55
50
3
4
5
7
6
V
CC
(V)
8
9
10
3494 G06
SHDN Current vs SHDN Voltage
20
PEAK INDUCTOR CURRENT (mA)
400
Peak Inductor Current (LT3494)
FIGURE 5 CIRCUIT
V
CC
= 3.6V
350 V
OUT
= 16V
700
PEAK INDUCTOR CURRENT (mA)
Peak Inductor Current (LT3494A)
FIGURE 6 CIRCUIT
V
CC
= 3.6V
650 V
OUT
= 16V
SHDN PIN CURRENT (μA)
15
300
250
200
150
100
–40 –20
600
550
500
450
400
–40 –20
10
5
0
0
2
10 12
4
6
8
SHDN PIN VOLTAGE (V)
14
16
0
20 40 60 80
TEMPERATURE (°C)
100 120
3494 G08
0
20 40 60 80
TEMPERATURE (°C)
100 120
3494 G09
3494 G07
LT3494 Switching Waveforms at
No Load
FIGURE 5 CIRCUIT
V
OUT
10mV/DIV
AC
COUPLED
V
OUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
LT3494 Switching Waveforms at
1mA Load
FIGURE 5 CIRCUIT
V
OUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
100mA/DIV
LT3494 Switching Waveforms at
25mA Load
FIGURE 5 CIRCUIT
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
50mA/DIV
V
CC
= 3.6V
V
OUT
= 16V
5μs/DIV
3494 G10
INDUCTOR
CURRENT
100mA/DIV
V
CC
= 3.6V
V
OUT
= 16V
2μs/DIV
3494 G11
V
CC
= 3.6V
V
OUT
= 16V
500ns/DIV
3494 G12
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LT3494/LT3494A
TYPICAL PERFORMANCE CHARACTERISTICS
LT3494A Switching Waveforms at
No Load
FIGURE 6 CIRCUIT
V
OUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
V
OUT
10mV/DIV
AC
COUPLED
SW
VOLTAGE
10V/DIV
T
A
= 25°C unless otherwise noted.
LT3494A Switching Waveforms at
30mA Load
V
OUT
10mV/DIV
AC
COUPLED
FIGURE 6 CIRCUIT
LT3494A Switching Waveforms at
5mA Load
FIGURE 6 CIRCUIT
SW
VOLTAGE
10V/DIV
INDUCTOR
CURRENT
200mA/DIV
V
CC
= 3.6V
V
OUT
= 16V
2
m
s/DIV
3494 G14
INDUCTOR
CURRENT
50mA/DIV
V
CC
= 3.6V
V
OUT
= 16V
5
m
s/DIV
3494 G13
INDUCTOR
CURRENT
100mA/DIV
V
CC
= 3.6V
V
OUT
= 16V
500ns/DIV
3494 G15
LT3494 Start-Up Waveforms
FIGURE 5 CIRCUIT
VOUT
VOLTAGE
50mV/DIV
AC COUPLED
LT3494 Transient Response
FIGURE 5 CIRCUIT
10mA→15mA→10mA LOAD PULSE
V
OUT
50mV/DIV
AC
COUPLED
LT3494A Transient Response
FIGURE 6 CIRCUIT
15mA→30mA→15mA LOAD PULSE
CAP
VOLTAGE
5V/DIV
VOUT
VOLTAGE
5V/DIV
INDUCTOR
CURRENT
100mA/DIV
INDUCTOR
CURRENT
100mA/DIV
INDUCTOR
CURRENT
200mA/DIV
V
CC
= 3.6V
V
OUT
= 16V
200μs/DIV
3494 G16
V
CC
= 3.6V
V
OUT
= 16V
100μs/DIV
3494 G17
V
CC
= 3.6V
V
OUT
= 16V
100μs/DIV
3494 G18
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