IC MULTI CONFIG ADJ 3A TO-263-5

LM2585SX-ADJ/NOPB

Manufacturer Part NumberLM2585SX-ADJ/NOPB
DescriptionIC MULTI CONFIG ADJ 3A TO-263-5
ManufacturerNational Semiconductor
SeriesSIMPLE SWITCHER®
TypeStep-Up (Boost), Flyback, Forward Converter
LM2585SX-ADJ/NOPB datasheet
 

Specifications of LM2585SX-ADJ/NOPB

Internal Switch(s)YesSynchronous RectifierNo
Number Of Outputs1Voltage - OutputAdjustable
Current - Output3AFrequency - Switching100kHz
Voltage - Input4 ~ 40 VOperating Temperature-40°C ~ 125°C
Mounting TypeSurface MountPackage / CaseD²Pak, TO-263 (5 leads + tab)
Primary Input Voltage40VNo. Of Outputs1
Output Voltage12.6VOutput Current3A
No. Of Pins5Operating Temperature Range-40°C To +125°C
Filter TerminalsSMDInput Voltage Primary Max40V
Rohs CompliantYesFor Use With551011367-061 - BOARD WEBENCH LM2577,LM2585/87
Lead Free Status / RoHS StatusLead free / RoHS CompliantPower - Output-
Other names*LM2585SX-ADJ
*LM2585SX-ADJ/NOPB
LM2585SX-ADJ
  
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CIRCUIT LAYOUT GUIDELINES
As in any switching regulator, layout is very important. Rapidly
switching currents associated with wiring inductance gener-
ate 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
41). 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, no heat sink is required to keep the LM2585
junction temperature within the allowed operating 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
LM2585). For a safe, conservative design, a temperature ap-
proximately 15°C cooler than the maximum junction temper-
ature should be selected (110°C).
4) LM2585 package thermal resistances θ
in the Electrical Characteristics).
Total power dissipated (P
) by the LM2585 can be estimated
D
as follows:
V
is the minimum input voltage, V
IN
N is the transformer turns ratio, D is the duty cycle, and
I
is the maximum load current (and
LOAD
the maximum load currents for multiple-output flyback regu-
lators). The duty cycle is given by:
www.national.com
FIGURE 41. Circuit Board Layout
Figure
where V
typically 0.5V for Schottky diodes and 0.8V for fast recovery
diodes. V
in the Characteristic Curves.
When no heat sink is used, the junction temperature rise is:
Adding the junction temperature rise to the maximum ambient
temperature gives the actual operating junction temperature:
If the operating junction temperature exceeds the maximum
junction temperatue in item 3 above, then a heat sink is re-
quired. When using a heat sink, the junction temperature rise
can be determined by the following:
and θ
(given
JA
JC
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 design software is a
more precise (non-linear) thermal model that can be used to
determine junction temperature with different input-output pa-
rameters or different component values. It can also calculate
the heat sink thermal resistance required to maintain the reg-
ulator junction temperature below the maximum operating
temperature.
To further simplify the flyback regulator design procedure,
National Semiconductor is making available computer design
is the output voltage,
OUT
software to be used with the Simple Switcher line of switching
regulators. Switchers Made Simple is available on a 3½
I
is the sum of
LOAD
diskette for IBM compatible computers from a National Semi-
conductor sales office in your area or the National Semicon-
ductor Customer Response Center (1-800-272-9959).
24
1251558
is the forward biased voltage of the diode and is
F
is the switch saturation voltage and can be found
SAT
ΔT
× θ
= P
.
J
D
JA
= ΔT
T
+ T
.
J
J
A
ΔT
× (θ
+ θ
+ θ
= P
J
D
JC
Interface
Heat Sink
= ΔT
T
+ T
J
J
A
)