Datasheet

LT3995
18
3995f
For more information www.linear.com/LT3995
With the OUT pin connected to the output, a 100mA ac-
tive load will charge the boost capacitor during light load
start-up and an enforced 500mV minimum dropout voltage
will keep the boost capacitor charged across operating
conditions (see Minimum Dropout Voltage section). This
yields excellent start-up and dropout performance. Figure 5
shows the minimum input voltage for 3.3V and 5V outputs.
Enable and Undervoltage Lockout
The LT3995 is in shutdown when the EN pin is low and
active when the pin is high. The falling threshold of the
EN comparator is 1.02V, with 60mV of hysteresis. The EN
pin can be tied to V
IN
if the shutdown feature is not used.
Undervoltage lockout (UVLO) can be added to the LT3995
as shown in Figure 6. Typically, UVLO is used in situa-
APPLICATIONS INFORMATION
Figure 5. The Minimum Input Voltage Depends on Output Voltage and Load Current
BOOST
LT3995
(4a) For 3.2V ≤ V
OUT
≤ 16V
GND
V
IN
V
IN
SW
OUT
V
OUT
BOOST
LT3995
(4d) For V
OUT
< 2.5V, 3.1V ≤ V
S
≤ 16V
GND
V
IN
V
IN
SW
OUT
V
OUT
V
S
BOOST
LT3995
(4e) For V
OUT
> 16V, 3.1V ≤ V
S
≤ 16V
GND
V
IN
V
IN
SW
OUT
V
OUT
3995 F04
V
S
BOOST
LT3995
(4c) For V
OUT
< 2.5V, V
IN
< 30V
GND
V
IN
V
IN
SW
OUT
V
OUT
BOOST
LT3995
(4b) For 2.5V ≤ V
OUT
≤ 3.2V
GND
V
IN
V
IN
SW
OUT
V
OUT
Figure 4. Five Circuits for Generating the Boost Voltage
Minimum Input Voltage, V
OUT
= 5V
Minimum Input Voltage, V
OUT
= 3.3V
LOAD CURRENT (A)
0
4.0
INPUT VOLTAGE (V)
4.5
5.0
5.5
6.0
6.5
0.5
1.0 1.5 2.0
3995 F05a
2.5 3.0
V
OUT
= 5V
f
SW
= 500kHz
TO RUN/TO START
LOAD CURRENT (A)
0
2.5
INPUT VOLTAGE (V)
3.0
3.5
4.0
4.5
5.0
0.5
1.0 1.5 2.0
3995 F05b
2.5 3.0
V
OUT
= 3.3V
FRONT PAGE APPLICATION
TO RUN/TO START