LT3686 LINER [Linear Technology], LT3686 Datasheet - Page 24

• Manufacturer Part Number: LT3686
• Manufacturer: LINER [Linear Technology]

LT3686
ApplicAtions inForMAtion
The die temperature is calculated by multiplying the LT3686
power dissipation by the thermal resistance from junction
to ambient. Power dissipation within the LT3686 can be
estimated by calculating the total power loss from an
efficiency measurement and subtracting the catch diode
loss. The resulting temperature rise at full load is nearly
independent of input voltage. Thermal resistance depends
on the layout of the circuit board, but 43°C/W is typical
for the (3mm × 3mm) DFN package.
Outputs Greater Than 19V
Note that for outputs above 19V, the input voltage range
will be limited by the maximum rating of the BOOST pin.
The sum of input and output voltages cannot exceed the

30V TO 36V
V
100nF
IN
2.2µF
Figure 18. 25V Step-Down Converter
61.9k
EN/UVLO
MODE
V
SS
RT
IN
LT3686
GND
BOOST pin’s 50V rating. The 25V circuit (Figure 18) shows
how to overcome this limitation using an additional Zener
diode.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for Buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
BOOST
SW
BD
DA
FB
10k
15V
0.22µF
100µH
301k
3686 F18
0.22µF
10µF
V
500mA
OUT
3686fa