Datasheet

LT3686
24
3686fc
SW
DA
FB
MODE
SS
RT
V
IN
V
IN
30V TO 36V
2.2µF
100nF
61.9k
10k
301k
100µH
0.22µF
0.22µF
10µF
15V
BD
V
OUT
500mA
GND
LT3686
3686 F18
EN/UVLO
BOOST
Figure 18. 25V Step-Down Converter
junction temperature. 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 subtract-
ing 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
BOOST pin’s 55V 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.
ApplicAtions inForMAtion