LT3508
3
3508fd
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25°C. V
IN
= 12V unless otherwise noted. (Note 2)
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 specifi cations
from 0°C to 125°C junction temperature. Specifi cations 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 fl ows 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 fl ows 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 specifi ed maximum operating junction temperature may impair
device reliability.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage, V
IN1
l
3.4 3.7 V
Minimum Operating Voltage, V
IN2
V
IN1
= 12V
l
2.5 3.0 V
V
IN1
Quiescent Current Not Switching 4.3 5.2 mA
V
IN2
Quiescent Current Not Switching 320 500 µA
Shutdown Current (V
IN1
+ V
IN2
)V
SHDN
= 0.3V 0.1 2 µA
FB Voltage
l
0.790
0.784
0.800 0.814
0.816
V
V
FB Pin Bias Current (Note 3) V
FB
= 0.800V, V
C
= 0.5V
l
50 300 nA
FB Voltage Line Regulation 5V < V
IN
< 40V 0.01 %/V
Error Amp Transconductance 300 µS
Error Amp Voltage Gain 600 V/V
V
C
to Switch Current Gain 2.5 A/V
Switching Frequency R
T
= 33.2k
l
0.92 1 1.06 MHz
Switching Phase R
T
= 33.2k 150 180 210 Deg
Maximum Duty Cycle (Note 4) R
T
= 33.2k
R
T
= 7.50k
R
T
= 169k
l
84 90
80
98
%
%
%
Foldback Frequency R
T
= 33.2k, V
FB
= 0V 120 kHz
Switch Current Limit (Note 5) Duty Cycle = 15%
l
2.0 2.6 3.2 A
Switch V
CESAT
I
SW
= 1.5A 300 mV
Switch Leakage Current 0.01 1 µA
Minimum Boost Voltage 1.7 2.5 V
Boost Pin Current I
SW
= 1.5A, V
BOOST
= 17V 35 50 mA
TRACK/SS Pin Current V
TRACK/SS
= 0V 0.8 1.2 2.2 µA
PG Threshold Offset V
FB
Rising 56 75 110 mV
PG Voltage Output Low V
FB
= 0.6V, I
PG
= 250µA 0.13 0.4 V
PG Pin Leakage V
PG
= 2V 0.01 1 µA
SHDN Threshold Voltage 2.53 2.63 2.73 V
SHDN Input Current (Note 6) V
SHDN
= 60mV Above Threshold Voltage 6 8 10 µA
SHDN Threshold Current Hysteresis 5.5 7.5 9.5 µA
SYNC Threshold Voltage 1 1.25 1.5 V
SYNC Input Frequency 0.25 2.5 MHz
