LM2574N-015G ON Semiconductor, LM2574N-015G Datasheet - Page 9

• Manufacturer Part Number: LM2574N-015G
• Description: IC REG SW 0.5A 15V OUTPUT 8-DIP
• Manufacturer: ON Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM2574N-015G

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 15V
• Current - Output: 500mA
• Frequency - Switching: 52kHz
• Voltage - Input: 4.75 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Output Voltage: 15 V
• Output Current: 0.5 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

Buck Converter Basics
is the most elementary forward−mode converter. Its basic
schematic can be seen in Figure 17.
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. Current now
flows through the catch diode thus maintaining the load
SO−16W
The LM2574 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.
12
14
4
6
3
5
V
in
Pin
Power
Switch
Figure 17. Basic Buck Converter
PDIP−8
I
5
7
2
4
1
3
L(on)
+
Feedback
Pwr Gnd
ON/OFF
D
Symbol
Sig Gnd
Output
V
V
in
in
– V out t on
L
L
This pin is the positive input supply for the LM2574 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
typically 1.0 V. It should 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 signal ground pin. See the information about the printed circuit board layout.
Circuit power 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 LM2574 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 input threshold voltage is typically 1.5 V.
Applying a voltage above this value (up to +V
pin is lower than 1.5 V or if this pin is left open, the regulator will be in the “on” condition.
C
out
PIN FUNCTION DESCRIPTION
DESIGN PROCEDURE
LM2574, NCV2574
http://onsemi.com
R
Load
9
Description (Refer to Figure 1)
current loop. This removes the stored energy from the
inductor. The inductor current during this time is:
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 18 shows the buck converter idealized waveforms
Figure 18. Buck Converter Idealized Waveforms
d +
Power
Switch
I
V
min
Diode
D
Off
(FWD)
in
t on
) shuts the regulator off. If the voltage applied to this
T
, where T is the period of switching.
I
V
in
L(off)
Power
Switch
on(SW)
Power
Switch
On
in Figure 1).
+
d +
V out – V
Switch
Power
Diode
Off
sat
V out
V
I
pk
in
of this output switch is
L
D
Switch
Power
Power
Switch
On
t
off
I
Load
Time
Time
(AV)