lt3502aidc-trpbf Linear Technology Corporation, lt3502aidc-trpbf Datasheet - Page 17

• Manufacturer Part Number: lt3502aidc-trpbf
• Description: 1.1mhz/2.2mhz, 500ma Step-down Regulators In 2mm X 2mm Dfn
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
High Temperature Considerations
The die temperature of the LT3502/LT3502A must be lower
than the maximum rating of 125°C. This is generally not
a concern unless the ambient temperature is above 85°C.
For higher temperatures, care should be taken in the layout
of the circuit to ensure good heat sinking of the LT3502/
LT3502A. The maximum load current should be derated as
the ambient temperature approaches 125°C. The die tem-
perature is calculated by multiplying the LT3502/LT3502A
power dissipation by the thermal resistance from junction
to ambient. Power dissipation within the LT3502/LT3502A
can be estimated by calculating the total power loss from
an effi ciency 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 102°C/W is typical
for the (2mm × 2mm) DFN package.
Outputs Greater Than 7V
Note that for outputs above 7V, 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 50V rating. The 15V circuit (Figure 12) shows
TYPICAL APPLICATIONS
3V TO 40V
3V TO 7V
V
V
BD
IN
OFF ON
C2
1μF
0.1μF
V
SHDN
IN
LT3502A
GND
BD
C1: JMK212BJ476MG
C3: HMK212BJ104MG
L1: LQH43CN3R3M03
BOOST
SW
DA
FB
C3
0.1μF
D1
3.3μH
L1
0.8V Step-Down Converter
3502 TA02a
C1
47μF
V
0.8V
500mA
OUT
how to overcome this limitation using an additional zener
diode.
Other Linear Technology Publications
Application notes AN19, AN35 and AN44 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.
20V TO 40V
3V TO 40V
3V TO 7V
V
V
V
BD
IN
IN
OFF ON
OFF ON
Figure 12. 15V Step-Down Converter
C2
1μF
C2
1μF
0.1μF
V
SHDN
V
SHDN
IN
IN
LT3502A
LT3502
GND
BD
LT3502/LT3502A
GND
BD
C1: JMK316BJ107ML
L1: LQH43CN100K03
BOOST
BOOST
SW
DA
FB
SW
DA
FB
R2
10k
C3
0.1μF
C3
0.1μF
D1
10V
180k
R1
33μH
10μH
L1
L1
22pF
17
3502 TA02b
3502 F12
C1
100μF
V
0.8V
500mA
C1
10μF
V
15V
500mA
OUT
3502fa
OUT