rent can be less than 7µA when operating and is ~0.3µA
when SWEN is low. The LT8494 can be configured as
either a SEPIC, boost or flyback converter.
The low ripple Burst Mode operation maintains high
efficiency at low output current while keeping output rip-
ple below 10mV. Dual supply pins (V
IN
and BIAS) allow
the part to automatically operate from the most efficient
supply. Input supply voltage can be up to 60V for SEPIC
topologies and up to 32V (with ride-through up to 60V)
for boost and flyback topologies. After start-up, battery
life is extended since the part can draw current from its
output (BIAS) even when V
IN
voltage drops below 2.5V.
Using a resistor divider on the SWEN pin provides a pro-
grammable undervoltage lockout (UVLO) for the con-
verter. A power good flag signals when V
OUT
reaches 92%
of the programmed output voltage.
Additional features such as frequency foldback and soft-
start are integrated. The LT8494 is available in 20-lead
QFN and 20-lead TSSOP packages with exposed pads
for low thermal resistance. Fault tolerance in the TSSOP
allows for adjacent pin shorts or an open without raising
the output voltage above its programmed value.
n
n
n
n
n
n
n
n
n
n
Low Ripple Burst Mode
®
Operation:
n
7µA I at 12V to 5V
Q
IN
OUT
n
Output Ripple (<10mV Typ.)
Dual Supply Pins:
n
Improves Efficiency
n
Reduces Minimum Supply Voltage to ~1V After
n
Start-Up to Extend Battery Life
Wide Input Voltage Range of ~1V to 60V (2.5V to
32V for Start-Up)
PG Functional for Input Supply Down to 1.3V
FMEA Fault Tolerant in TSSOP Package
Fixed Frequency PWM, SEPIC/BOOST/FLYBACK
Topologies
NPN Power Switch: 2A/70V
Programmable Switching Frequency: 250kHz to 1.5MHz
UVLO Programmable on SWEN Pin
Soft-Start Programmable with One Capacitor
Small 20-Lead QFN or 20-Lead TSSOP Packages
APPLICATIONS
n
n
n
Automotive ECU Power
Power for Portable Products
Industrial Supplies
L,
LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks of
Analog Devices, Inc. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
450kHz, 5V Output SEPIC Converter
V
IN
3V TO 60V
15µH
No-Load Supply Current
20
V
OUT
5V
0.35A (V
IN
= 3V)
0.6A (V
IN
= 5V)
1.0A (V
IN
> 12V)
90
85
SUPPLY CURRENT (µA)
15
EFFICIENCY (%)
80
75
70
65
0
60
0.0
Efficiency
V
IN
= 24V
V
IN
= 12V
V
IN
= 5V
•
2.2µF
4.7µF
V
IN
SW
BIAS
SWEN
LT8494
PG
RT SS
GND FB
169k
1µF
•
15µH
1M
4.7pF
316k
10
47µF
×2
8494 TA01a
5
0
12
24
36
INPUT VOLTAGE (V)
48
60
8494 TA01b
0.2
0.4
0.6
LOAD CURRENT (A)
0.8
1.0
8494 TA01c
8494fa
For more information
www.linear.com/LT8494
1
LT8494
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
, BIAS Voltage ......................................................60V
SWEN Voltage ...........................................................60V
FB Voltage .................................................................60V
SW Voltage ...............................................................70V
PG Voltage ..................................................................6V
RT Voltage ..................................................................6V
SS Voltage ..................................................................3V
Operating Junction Temperature Range
LT8494E, LT8494I (Notes 2, 3) .......... –40°C to 125°C
LT8494H (Notes 2, 3) ........................ –40°C to 150°C
Storage Temperature Range .............. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package ....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
BIAS
PG
NC
NC
FB
BIAS
FB
15 GND
21
GND
14 GND
13 GND
12 SW
11 GND
6
SWEN
7
NC
8
NC
9 10
GND
V
IN
FB
NC
NC
NC
PG
SS
NC
1
2
3
4
5
6
7
8
9
21
GND
TOP VIEW
20 SW
19 NC
18 V
IN
17 NC
16 GND
15 NC
14 GND
13 NC
12 SWEN
11 NC
20 19 18 17 16
SS 1
RT 2
GND 3
GND 4
NC 5
RT 10
UF PACKAGE
20-LEAD (4mm
×
4mm) PLASTIC QFN
θ
JA
= 47°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
FE PACKAGE
20-LEAD PLASTIC TSSOP
θ
JA
= 38°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT8494EUF#PBF
LT8494IUF#PBF
LT8494EFE#PBF
LT8494IFE#PBF
LT8494HFE#PBF
TAPE AND REEL
LT8494EUF#TRPBF
LT8494IUF#TRPBF
LT8494EFE#TRPBF
LT8494IFE#TRPBF
LT8494HFE#TRPBF
http://www.linear.com/product/LT8494#orderinfo
PART MARKING*
8494
8494
LT8494FE
LT8494FE
LT8494FE
PACKAGE DESCRIPTION
20-Lead (4mm
×
4mm) Plastic QFN
20-Lead (4mm
×
4mm) Plastic QFN
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
8494fa
For more information
www.linear.com/LT8494
LT8494
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
SWEN
= 12V, V
BIAS
= 5V, unless otherwise noted (Note 2).
PARAMETER
Minimum V
IN
Operating Voltages
Minimum BIAS Operating Voltages
Power Switch Driver (PSD) Overvoltage Threshold
(Note 4)
Power Switch Driver (PSD) Overvoltage Threshold
Hysteresis (Note 4)
Quiescent Current from V
IN
V
SWEN
= 0V
V
SWEN
= 5V, V
FB
= 1.25V
V
SWEN
= 5V, V
FB
= 1.25V (LT8494E, LT8494I)
V
SWEN
= 5V, V
FB
= 1.25V (LT8494H)
V
SWEN
= 0V
V
SWEN
= 5V, V
FB
= 1.25V
V
SWEN
= 5V, V
FB
= 1.25V (LT8494E, LT8494I)
V
SWEN
= 5V, V
FB
= 1.25V (LT8494H)
V
BIAS
-V
IN
, V
BIAS
Rising, V
IN
= 12V
V
BIAS
-V
IN
, V
BIAS
Falling, V
IN
= 12V
Hysteresis (Rising-Falling Threshold)
V
FB
= 1.202V
5V ≤ V
IN
≤ 32V, BIAS = 5V
5V ≤ V
IN
≤ 32V, BIAS = 0V
CONDITIONS
V
BIAS
< 2.5V
V
BIAS
≥ 2.5V
V
IN
< 2.5V
V
IN
≥ 2.5V
V
IN
or BIAS Rising
V
IN
or BIAS Falling
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
MIN
TYP
2.4
2.4
MAX
2.5
0
2.5
0
36.5
36.4
UNITS
V
V
V
V
V
V
mV
32.1
32
34
33.9
100
0.3
3.0
3.0
3.0
0.07
1.7
1.7
1.7
l
l
0.9
4.8
6.2
8.0
0.5
2.8
3.5
10
1.2
0.57
0.8
1.230
20
10
10
µA
µA
µA
µA
µA
µA
µA
µA
V
V
V
V
nA
m%/V
m%/V
ns
ns
Quiescent Current from BIAS
l
l
l
l
l
l
BIAS to V
IN
Comparator Threshold
Feedback Voltage
FB Pin Bias Current (Note 7)
FB Voltage Line Regulation
Minimum Switch Off-Time
Minimum Switch On-Time
Switching Frequency
Switch Current Limit at Minimum Duty Cycle (Note 5)
Switch Current Limit at Maximum Duty Cycle (Note 6)
Switch V
CESAT
Switch Leakage Current (Note 7)
Soft-Start Charging Current (Note 7)
SWEN Pin Current (Note 7)
0.55
0.17
0.20
1.178
0.9
0.37
0.53
1.202
0.1
0.2
0.2
70
95
R
T
= 68.1k
R
T
= 324k
l
l
l
l
0.92
219
2.1
1.3
1.0
250
2.55
1.85
340
0.01
1.06
280
2.95
2.4
1
12.2
25
200
550
1.1
97
93
150
150
150
0.3
1.0
MHz
kHz
A
A
mV
μA
μA
nA
nA
nA
V
mV
%
%
mV
mV
mV
mV
μA
μA
I
SW
= 1.2A
V
SW
= 12V, V
SWEN
= 0V
V
SS
= 100mV
V
SWEN
= 1.2V
V
SWEN
= 5V
V
SWEN
= 12V
l
l
5.2
8.2
0
35
240
SWEN Rising Voltage Threshold
SWEN Voltage Hysteresis
PG Threshold as % of V
FB
Regulation Voltage
PG Hysteresis
PG Output Voltage Low
I
SINK
= 1.25mA
I
SINK
= 100μA, V
BIAS
= 0V, V
IN
= 1.3V
I
SINK
= 100μA, V
BIAS
= 1.3V, V
IN
= 0V
V
PG
= 5V (LT8494E, LT8494I)
V
PG
= 5V (LT8494H)
V
FB
Rising
V
FB
Falling
0.9
86
82
1
30
92
88
46
33
15
15
0
0
l
l
l
l
l
l
l
PG Leakage Current
8494fa
For more information
www.linear.com/LT8494
3
LT8494
ELECTRICAL CHARACTERISTICS
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. Voltages are with respect to GND pin unless
otherwise noted.
Note 2:
The LT8494E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT8494I is guaranteed to meet performance specifications from –40°C
to 125°C junction temperature. The LT8494H is guaranteed over the full
–40°C to 150°C operating junction temperature range. Operation lifetime is
derated at junction temperatures greater than 125°C.
Note 3:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions.
Junction temperature will exceed the maximum operating range when
overtemperature protection is active. Continuous operation above the
specified maximum operating junction temperature may impair device
reliability.
Note 4:
See Power Supplies and Operating Limits in the Applications
Information section for more details.
Note 5:
Current limit guaranteed by design and/or correlation to static test.
Slope Compensation reduces current limit at higher duty cycles.
Note 6:
Max duty cycle current limit measured at 1MHz switching
frequency.
Note 7:
Polarity specification for all currents into pins is positive. All
voltages are referenced to GND unless otherwise specified.
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