EXPOSED PAD (PIN 17) IS GND AND MUST BE SOLDERED TO PCB
UF PACKAGE
24-LEAD (4mm 4mm) PLASTIC QFN
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 25) IS GND AND MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3508EFE#PBF
LT3508IFE#PBF
LT3508HFE#PBF
LT3508EUF#PBF
LT3508IUF#PBF
LT3508HUF#PBF
TAPE AND REEL
LT3508EFE#TRPBF
LT3508IFE#TRPBF
LT3508HFE#TRPBF
LT3508EUF#TRPBF
LT3508IUF#TRPBF
LT3508HUF#TRPBF
PART MARKING*
3508FE
3508FE
3508HFE
3508
3508
3508H
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
24-Lead (4mm
×
4mm) Plastic QFN
24-Lead (4mm
×
4mm) Plastic QFN
24-Lead (4mm
×
4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°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.*Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
3508fb
2
LT3508
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating Voltage, V
IN1
Minimum Operating Voltage, V
IN2
V
IN1
Quiescent Current
V
IN2
Quiescent Current
Shutdown Current (V
IN1
+ V
IN2
)
FB Voltage
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
Error Amp Transconductance
Error Amp Voltage Gain
V
C
to Switch Current Gain
Switching Frequency
Switching Phase
Maximum Duty Cycle (Note 4)
R
T
= 33.2k
R
T
= 33.2k
R
T
= 33.2k
R
T
= 7.50k
R
T
= 169k
R
T
= 33.2k, V
FB
= 0V
Duty Cycle = 15%
I
SW
= 1.5A
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
BOOST
= 17V unless otherwise noted. (Note 2)
CONDITIONS
l
MIN
l
TYP
3.4
2.5
4.3
320
0.1
MAX
3.7
3.0
5.2
500
2
0.814
0.816
300
UNITS
V
V
mA
μA
μA
V
V
nA
%/V
μS
V/V
A/V
V
IN1
= 12V
Not Switching
Not Switching
V
SHDN
= 0.3V
l
0.790
0.784
0.800
50
0.01
300
600
2.5
V
FB
= 0.800V, V
C
= 0.4V
5V < V
IN
< 40V
l
0.92
150
84
1
180
90
80
98
120
2.6
300
0.01
1.7
1.06
210
MHz
Deg
%
%
%
kHz
Foldback Frequency
Switch Current Limit (Note 5)
Switch V
CESAT
Switch Leakage Current
Minimum Boost Voltage
Boost Pin Current
TRACK/SS Pin Current
PG Threshold Offset
PG Voltage Output Low
PG Pin Leakage
SHDN
Threshold Voltage
SHDN
Input Current (Note 6)
SHDN
Threshold Current Hysteresis
SYNC Threshold Voltage
SYNC Input Frequency
2.0
3.2
1
2.5
50
2.2
110
0.4
1
2.73
10
9.5
1.5
2.5
A
mV
μA
V
mA
μA
mV
V
μA
V
μA
μA
V
MHz
I
SW
= 1.5A
V
TRACK/SS
= 0V
V
FB
Rising
V
FB
= 0.6V, I
PG
= 250μA
V
PG
= 2V
2.53
V
SHDN
= 60mV Above Threshold Voltage
6
5.5
1
0.25
0.8
56
35
1.2
75
0.13
0.01
2.63
8
7.5
1.25
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 LT3508E 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
LT3508I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3508H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C.
Note 3:
Current flows out of pin.
Note 4:
V
BOOST
=12V. Circuitry increases the maximum duty cycle of the
LT3508 when V
BOOST
> V
IN
+ 2.5V. See “Minimum Operating Voltage” in
the Applications Information section for details.
Note 5:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
Note 6:
Current flows into pin.
Note 7:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
range when overtemperature protection is active. Continuous operation
above the specified maximum operating junction temperature may impair
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