IC, STEP-DOWN VOLTAGE REGULATOR, TO-220

LM2596T-ADJ

Manufacturer Part NumberLM2596T-ADJ
DescriptionIC, STEP-DOWN VOLTAGE REGULATOR, TO-220
ManufacturerNational Semiconductor
LM2596T-ADJ datasheet
 


Specifications of LM2596T-ADJ

Primary Input Voltage40VNo. Of Outputs1
Output Voltage37VOutput Current3A
No. Of Pins5Operating Temperature Range-40°C To +125°C
Supply Voltage Range4.5V To 40VFilter TerminalsThrough Hole
Rohs CompliantYesLead Free Status / RoHS StatusLead free / RoHS Compliant
1
2
3
4
5
6
7
8
9
10
11
Page 11
12
Page 12
13
Page 13
14
Page 14
15
Page 15
16
Page 16
17
Page 17
18
Page 18
19
Page 19
20
Page 20
21
22
23
24
25
26
27
28
29
30
31
Page 19/31

Download datasheet (737Kb)Embed
PrevNext
Block Diagram
Application Information
PIN FUNCTIONS
+V
— This is the positive input supply for the IC switching
IN
regulator. A suitable input bypass capacitor must be present
at this pin to minimize voltage transients and to supply the
switching currents needed by the regulator.
Ground — Circuit ground.
Output — Internal switch. The voltage at this pin switches
between (+V
− V
) and approximately −0.5V, with a duty
IN
SAT
cycle of approximately V
/V
. To minimize coupling to
OUT
IN
sensitive circuitry, the PC board copper area connected to
this pin should be kept to a minimum.
Feedback — Senses the regulated output voltage to com-
plete the feedback loop.
ON /OFF — Allows the switching regulator circuit to be shut
down using logic level signals thus dropping the total input
supply current to approximately 80 µA. Pulling this pin below
a threshold voltage of approximately 1.3V turns the regulator
on, and pulling this pin above 1.3V (up to a maximum of 25V)
shuts the regulator down. If this shutdown feature is not
needed, the ON /OFF pin can be wired to the ground pin or
it can be left open, in either case the regulator will be in the
ON condition.
EXTERNAL COMPONENTS
INPUT CAPACITOR
C
— A low ESR aluminum or tantalum bypass capacitor is
IN
needed between the input pin and ground pin. It must be
located near the regulator using short leads. This capacitor
prevents large voltage transients from appearing at the in-
put, and provides the instantaneous current needed each
time the switch turns on.
The important parameters for the Input capacitor are the
voltage rating and the RMS current rating. Because of the
FIGURE 12.
relatively high RMS currents flowing in a buck regulator’s
input capacitor, this capacitor should be chosen for its RMS
current rating rather than its capacitance or voltage ratings,
although the capacitance value and voltage rating are di-
rectly related to the RMS current rating.
The RMS current rating of a capacitor could be viewed as a
capacitor’s power rating. The RMS current flowing through
the capacitors internal ESR produces power which causes
the internal temperature of the capacitor to rise. The RMS
current rating of a capacitor is determined by the amount of
current required to raise the internal temperature approxi-
mately 10˚C above an ambient temperature of 105˚C. The
ability of the capacitor to dissipate this heat to the surround-
ing air will determine the amount of current the capacitor can
safely sustain. Capacitors that are physically large and have
a large surface area will typically have higher RMS current
ratings. For a given capacitor value, a higher voltage elec-
trolytic capacitor will be physically larger than a lower voltage
capacitor, and thus be able to dissipate more heat to the
surrounding air, and therefore will have a higher RMS cur-
rent rating.
The consequences of operating an electrolytic capacitor
above the RMS current rating is a shortened operating life.
The higher temperature speeds up the evaporation of the
capacitor’s electrolyte, resulting in eventual failure.
Selecting an input capacitor requires consulting the manu-
facturers data sheet for maximum allowable RMS ripple
current. For a maximum ambient temperature of 40˚C, a
general guideline would be to select a capacitor with a ripple
current rating of approximately 50% of the DC load current.
For ambient temperatures up to 70˚C, a current rating of
75% of the DC load current would be a good choice for a
conservative design. The capacitor voltage rating must be at
least 1.25 times greater than the maximum input voltage,
and often a much higher voltage capacitor is needed to
satisfy the RMS current requirements.
19
01258321
www.national.com