LM2576TV-5G ON Semiconductor, LM2576TV-5G Datasheet - Page 9

IC REG SW 3A 5V STEPDOWN TO220-5

LM2576TV-5G

Manufacturer Part Number
LM2576TV-5G
Description
IC REG SW 3A 5V STEPDOWN TO220-5
Manufacturer
ON Semiconductor
Type
Step-Down (Buck)r
Datasheet

Specifications of LM2576TV-5G

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
5V
Current - Output
3A
Frequency - Switching
52kHz
Voltage - Input
7 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Through Hole
Package / Case
TO-220-5 (Bent and Staggered Leads)
Output Voltage
5 V
Output Current
3 A
Input Voltage
4.75 V to 40 V
Switching Frequency
52 KHz
Operating Temperature Range
- 40 C to + 125 C
Mounting Style
Through Hole
Duty Cycle (max)
98 %
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Lead Free Status / Rohs Status
Lead free / RoHS Compliant

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Buck Converter Basics
is the most elementary forward−mode converter. Its basic
schematic can be seen in Figure 16.
time periods. The first one occurs when the series switch is
on, the input voltage is connected to the input of the inductor.
rectifier (or catch diode) is reverse biased. During this
period, since there is a constant voltage source connected
across the inductor, the inductor current begins to linearly
ramp upwards, as described by the following equation:
material in the form of magnetic flux. If the inductor is
properly designed, there is sufficient energy stored to carry
the requirements of the load during the “off” period.
When the power switch turns off, the voltage across the
inductor reverses its polarity and is clamped at one diode
voltage drop below ground by the catch diode. The current
now flows through the catch diode thus maintaining the load
current loop. This removes the stored energy from the
inductor. The inductor current during this time is:
PIN FUNCTION DESCRIPTION
Pin
The LM2576 is a “Buck” or Step−Down Converter which
The operation of this regulator topology has two distinct
The output of the inductor is the output voltage, and the
During this “on” period, energy is stored within the core
The next period is the “off” period of the power switch.
1
2
3
4
5
V
Feedback
in
ON/OFF
Symbol
Output
GND
V
in
Power
Switch
Figure 16. Basic Buck Converter
I
I
L(on)
L(off)
This pin is the positive input supply for the LM2576 step−down switching regulator. In order to minimize voltage
transients and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be
present (C
This is the emitter of the internal switch. The saturation voltage V
be kept in mind that the PCB area connected to this pin should be kept to a minimum in order to minimize coupling
to sensitive circuitry.
Circuit ground pin. See the information about the printed circuit board layout.
This pin senses regulated output voltage to complete the feedback loop. The signal is divided by the internal resistor
divider network R2, R1 and applied to the non−inverting input of the internal error amplifier. In the Adjustable version
of the LM2576 switching regulator this pin is the direct input of the error amplifier and the resistor network R2, R1 is
connected externally to allow programming of the output voltage.
It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply
current to approximately 80 mA. The threshold voltage is typically 1.4 V. Applying a voltage above this value (up to
+V
regulator will be in the “on” condition.
in
+
+
) shuts the regulator off. If the voltage applied to this pin is lower than 1.4 V or if this pin is left open, the
D
V
V out – V
in
in
– V out t on
in Figure 1).
L
L
L
D
t
off
C
out
DESIGN PROCEDURE
http://onsemi.com
R
Load
Description (Refer to Figure 1)
LM2576
9
turned on. Regulation of the converter is accomplished by
varying the duty cycle of the power switch. It is possible to
describe the duty cycle as follows:
cycle can also be described as:
of the catch diode voltage and the inductor current.
This period ends when the power switch is once again
For the buck converter with ideal components, the duty
Figure 17 shows the buck converter, idealized waveforms
d +
Figure 17. Buck Converter Idealized Waveforms
t on
I
Switch
Power
V
min
Diode
T
D
Off
(FWD)
, where T is the period of switching.
sat
of this output switch is typically 1.5 V. It should
V
on(SW)
Switch
Power
Switch
Power
On
d +
Switch
Power
Diode
Off
V out
V
I
pk
in
Power
Switch
Switch
Power
On
I
Load
Time
Time
(AV)

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