Datasheet

LM2586
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SNVS121D MAY 1996REVISED APRIL 2013
Figure 59. Circuit Board Layout
CIRCUIT LAYOUT GUIDELINES
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring
inductance generate voltage transients which can cause problems. For minimal inductance and ground loops,
keep the length of the leads and traces as short as possible. Use single point grounding or ground plane
construction for best results. Separate the signal grounds from the power grounds (as indicated in Figure 59).
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 temperature should be selected (110°C).
4) LM2586 package thermal resistances θ
JA
and θ
JC
(given in the Electrical Characteristics).
Total power dissipated (P
D
) by the LM2586 can be estimated as follows:
where
V
IN
is the minimum input voltage
V
OUT
is the output voltage
N is the transformer turns ratio, D is the duty cycle
I
LOAD
is the maximum load current (and I
LOAD
is the sum of the maximum load currents for multiple-output
flyback regulators) (7)
The duty cycle is given by:
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