LT3645
4
3645f
Buck Minimum Input Voltage,
V
OUT
= 3.3V
Effi ciency V
OUT
= 5V Effi ciency V
OUT
= 3.3V
Buck Minimum Input Voltage,
V
OUT
= 5V
PARAMETER CONDITIONS MIN TYP MAX UNITS
FB NPG Threshold, % of Regulation Voltage V
FB2
= 800mV, V
FB
Rising 88 90 92 %
NPG Threshold Hysteresis 25 mV
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, BOOST = 15.3V, V
CC2
= 3.3V, OUT2 = 1.8V unless
otherwise noted. (Notes 2, 3)
Note1: 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 LT3645E is guaranteed to meet performance specifi cations
from 0°C to 125°C. Specifi cations over the –40°C to 125°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3645I is guaranteed over the full
–40°C to 125°C operating temperature range. The LT3645H is guaranteed
over the full –40°C to 150°C operating temperature range. High junction
temperatures degrade operating lifetimes. Operating 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 junction operating temperature
when overtemperature protection is active. Continuous operation above
the specifi ed maximum operating junction temperature may result in
device degradation or failure.
Note 4: Current Measurements are performed when the outputs are not
switching. Slope compensation reduces current limit at high duty cycles.
Note 5: Absolute Maximum Voltage at V
IN
and EN/UVLO pins is 55V for
nonrepetitive one second transients, and 36V for continuous operation.
FB2 Voltage
TYPICAL PERFORMANCE CHARACTERISTICS
OUTPUT CURRENT (mA)
0
50
EFFICIENCY (%)
60
70
80
90
100
200 300
3645 G01
400 500
V
IN
= 7V
V
IN
= 12V
V
IN
= 24V
LOAD CURRENT (mA)
0
50
EFFICIENCY (%)
60
70
80
90
100
200 300
3645 G02
400 500
V
IN
= 7V
V
IN
= 12V
V
IN
= 24V
OUTPUT CURRENT (mA)
1
5.0
INPUT VOLTAGE (V)
5.5
6.5
6.0
7.5
7.0
8.0
10
100
3645 G03
1000
V
IN
TO RUN
V
IN
TO START
TEMPERATURE (°C)
–50 –30 –10
794
FB VOLTAGE (mV)
796
799
798
797
795
800
801
802
803
804
10 30 50
70 90 130
3645 G05
110 150
FB Voltage
TEMPERATURE (°C)
–50 0
794
FB VOLTAGE (mV)
795
797
796
798
799
800
50
3645 G06
100 150
OUTPUT CURRENT (mA)
1
3.0
INPUT VOLTAGE (V)
4.0
3.5
5.0
4.5
6.0
5.5
6.5
10
100
3645 G04
1000
V
IN
TO RUN
V
IN
TO START
