LT3580 LINER [Linear Technology], LT3580 Datasheet - Page 15

• Manufacturer Part Number: LT3580
• Description: Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start, and Synchronization
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
the regulator from operating at source voltages where
these problems might occur.
The shutdown pin comparator has voltage hysteresis with
typical thresholds of 1.32V (rising) and 1.29V (falling).
Resistor R
reduce the overall UVLO voltage variation caused by varia-
tions in SHDN pin current (see the Electrical Character-
istics). A good choice for R
After choosing a value for R
mined from either of the following:
where V
falling respectively.
For example, to disable the LT3580 for V
3.5V using the single resistor confi guration, choose:
or
V
R
R
R
IN
UVLO1
UVLO1
UVLO1
IN
R
R
(OPTIONAL)
+
UVLO1
UVLO2
=
=
=
UVLO2
and V
R
R
1.29V
1.32V
1.29V
3.5V 1.29V
Figure 7. Confi gurable UVLO
UVLO2
UVLO2
V
V
is optional. R
IN
IN
IN
V
SHDN
GND
–
IN
+
are the V
AT 1.3V
+ 11.6μA
11.6μA
1.32V
1.29V
+ 11.6μA
+ 11.6μA
UVLO2
1.3V
IN
UVLO2
voltages when rising or
= 190.5k
UVLO2
, R
–
+
UVLO1
can be included to
IN
is ≤10k ±1%.
voltages below
can be deter-
LOCKOUT
ACTIVE/
3580 F07
To activate the LT3580 for V
using the double resistor confi guration, choose R
= 10k and:
Internal Undervoltage Lockout
The LT3580 monitors the V
drops below a minimum operating level (typically about
2.3V). When V
deactivated, and while suffi cient V
soft-start capacitor is discharged. After V
high, the power switch will be reactivated and the soft-
start capacitor will begin charging.
Thermal Considerations
For the LT3580 to deliver its full output power, it is impera-
tive that a good thermal path be provided to dissipate the
heat generated within the package. This is accomplished
by taking advantage of the thermal pad on the underside of
the IC. It is recommended that multiple vias in the printed
circuit board be used to conduct heat away from the IC
and into a copper plane with as much area as possible.
Thermal Lockout
If the die temperature reaches approximately 165°C, the
part will go into thermal lockout, the power switch will be
turned off and the soft-start capacitor will be discharged.
The part will be enabled again when the die temperature
has dropped by ~5°C (nominal).
Thermal Calculations
Power dissipation in the LT3580 chip comes from four
primary sources: switch I
NPN base drive (DC), and additional input current. The
following formulas can be used to approximate the power
losses. These formulas assume continuous mode opera-
R
UVLO1
=
1.32V
IN
10k
4.5V 1.32V
is detected low, the power switch is
+ 11.6μA
2
R loss, NPN base drive (AC),
IN
IN
supply voltage in case V
voltage greater than 4.5V
= 22.1k
IN
voltage persists, the
IN
LT3580
is detected
15
UVLO2
3580fc
IN