Datasheet

LT3474/LT3474-1
3
3474fd
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.
Note 2: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specifi ed maximum operating junction
temperature may impair device reliability.
Note 3: The LT3474E and LT3474E-1 are guaranteed to meet performance
specifi cations from 0°C to 70°C. Specifi cations over the –40°C to 85°C
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, V
BOOST
= 16V, V
OUT
= 4V unless otherwise noted (Note 3).
PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference Voltage Line Regulation 5V < V
IN
< 36V 0.01 %/V
Reference Voltage Load Regulation 0 < I
REF
< 250μA 0.0002 %/μA
V
ADJ
Pin Bias Current (Note 4)
l
20 400 nA
Switching Frequency R
T
= 80.6k
l
470
450
500 530
540
kHz
kHz
Maximum Duty Cycle R
T
= 80.6k
R
T
= 10k
R
T
= 232k
l
90 95
76
98
%
%
%
Foldback Frequency R
T
= 80.6k, V
OUT
= 0V 70 kHz
SHDN Threshold (to Switch) 2.6 2.65 2.7 V
SHDN Pin Current (Note 5) V
SHDN
= SHDN Threshold 8.3 10.3 12.3 μA
PWM Threshold 0.4 0.9 1.2 V
V
C
Switching Threshold 0.8 V
V
C
Source Current V
C
= 1V 100 μA
V
C
Sink Current V
C
= 1V 100 μA
LED to V
C
Current Gain 1.5 μA/mA
LED to V
C
Transresistance 1 V/mA
V
C
to Switch Current Gain 2A/V
V
C
Clamp Voltage 1.9 V
V
C
Pin Current in PWM Mode V
C
= 1V, V
PWM
= 0.3V
l
0.01 1 μA
OUT Pin Clamp Voltage (LT3474) 13.2 13.8 14.5 V
OUT Pin Current in PWM Mode V
OUT
= 4V, V
PWM
= 0.3V
l
0.1 10 μA
Switch Current Limit (Note 6) –40°C to 85°C
LT3474I, LT3474I-1 at 125°C
l
1.6
1.5
2.1 3.2
3.2
A
A
Switch V
CESAT
I
SW
= 1A 380 500 mV
Boost Pin Current I
SW
= 1A 30 50 mA
Switch Leakage Current 0.01 1 μA
Minimum Boost Voltage (Note 7) 1.9 2.5 V
Boost Diode Forward Voltage I
DIO
= 100mA 600 mV
operating temperature range are assured by design, characterization and
correlation with statistical process controls. The LT3474I and LT3474I-1
are guaranteed to meet performance specifi cations over the –40°C to
125°C operating temperature range.
Note 4: Current fl ows out of pin.
Note 5: Current fl ows into pin.
Note 6: Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
Note 7: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.