LM2586S-ADJ National Semiconductor, LM2586S-ADJ Datasheet - Page 28

• Manufacturer Part Number: LM2586S-ADJ
• Description: IC, FLYBACK REGULATOR, TO-263-7
• Manufacturer: National Semiconductor

Specifications of LM2586S-ADJ

• Primary Input Voltage: 40V
• No. Of Outputs: 1
• Output Voltage: 37V
• Output Current: 3A
• No. Of Pins: 7
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 3 - 168 Hours
• Supply Voltage Range: 4V To 40V
• Filter Terminals: SMD
• Rohs Compliant: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Application Hints
indicated in Figure 45). When using the Adjustable version,
physically locate the programming resistors as near the
regulator IC as possible, to keep the sensitive feedback
wiring short.
HEAT SINK/THERMAL CONSIDERATIONS
In many cases, a heat sink is not required to keep the
LM2586 junction temperature within the allowed operating
temperature range. For each application, to determine
whether or not a heat sink will be required, the following must
be identified:
1) Maximum ambient temperature (in the application).
2) Maximum regulator power dissipation (in the application).
3) Maximum allowed junction temperature (125˚C for the
LM2586). For a safe, conservative design, a temperature
approximately 15˚C cooler than the maximum junction tem-
perature should be selected (110˚C).
4) LM2586 package thermal resistances θ
in the Electrical Characteristics).
Total power dissipated (P
as follows:
V
N is the transformer turns ratio, D is the duty cycle, and I
is the maximum load current (and
maximum load currents for multiple-output flyback regula-
tors). The duty cycle is given by:
where V
typically 0.5V for Schottky diodes and 0.8V for fast recovery
diodes. V
found in the Characteristic Curves.
When no heat sink is used, the junction temperature rise is:
IN
is the minimum input voltage, V
F
SAT
is the forward biased voltage of the diode and is
is the switch saturation voltage and can be
∆T
J
D
) by the LM2586 can be estimated
= P
D
(Continued)
• θ
OUT
∑
JA
I
.
LOAD
is the output voltage,
JA
is the sum of the
and θ
JC
(given
LOAD
28
Adding the junction temperature rise to the maximum ambi-
ent temperature gives the actual operating junction tempera-
ture:
If the operating junction temperature exceeds the maximum
junction temperatue in item 3 above, then a heat sink is
required. When using a heat sink, the junction temperature
rise can be determined by the following:
Again, the operating junction temperature will be:
As before, if the maximum junction temperature is exceeded,
a larger heat sink is required (one that has a lower thermal
resistance).
Included in the Switchers Made Simple
a more precise (non-linear) thermal model that can be used
to determine junction temperature with different input-output
parameters or different component values. It can also calcu-
late the heat sink thermal resistance required to maintain the
regulator junction temperature below the maximum operat-
ing temperature.
To further simplify the flyback regulator design procedure,
National Semiconductor is making available computer de-
sign software to be used with the Simple Switcher
switching regulators. Switchers Made Simple is available
on a 3
National Semiconductor sales office in your area or the
National
(1-800-272-9959).
1
⁄
2
" diskette for IBM compatible computers from a
∆T
Semiconductor
J
= P
D
• (θ
T
T
J
JC
J
= ∆T
= ∆T
+ θ
Customer
Interface
J
J
+ T
+ T
A
A
.
+ θ
®
Response
Heat Sink
design software is
)
®
Center
line of