ncp1536 ON Semiconductor, ncp1536 Datasheet - Page 7

• Manufacturer Part Number: ncp1536
• Description: 3.0 A, Step-down Switching Regulator
• Manufacturer: ON Semiconductor

Procedure In order to simplify the switching regulator design, a step−by−step design procedure and some
examples are provided.
Given Parameters:
1. Programming Output Voltage
2. Input Capacitor Selection (C
3. Catch Diode Selection (D1)
V
V
I
To select the right programming resistor R1 and R2 value
use the following formula:
Resistor R1 can be between 1.0 k and 5.0 kW. (For best
temperature coefficient and stability with time, use 1% metal
film resistors).
To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +V
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.
For additional information see input capacitor section in the
“Application Hints” section of this data sheet.
A. Since the diode maximum peak current exceeds the
B. The reverse voltage rating of the diode should be at least
Load(max)
out
in(max)
regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design, the diode should have a
current rating equal to the maximum current limit of the
NCP1536 to be able to withstand a continuous output short.
1.25 times the maximum input voltage.
= Regulated Output Voltage
V out + V
= Maximum DC Input Voltage
= Maximum Load Current
in
and ground pin GND This capacitor should be
ref
R2 + R1
1.0 )
Procedure
R2
R1
V out
V
in
ref
)
where V
– 1.0
ref
= 1.23 V
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NCP1536
7
Given Parameters:
1. Programming Output Voltage (selecting R1 and R2)
2. Input Capacitor Selection (C
the input and ground pin provides sufficient bypassing.
3. Catch Diode Selection (D1)
V
V
I
Select R1 and R2:
A 100 mF, 150 V aluminium electrolytic capacitor located near
A. For this example, a 3.0 A current rating is adequate.
B. Use a 30 V 1N5821 Schottky diode or any suggested fast
Load(max)
out
in(max)
R2 = 9.91 kW, choose a 9.88 k metal film resistor.
recovery diode in the Table 1.
= 8.0 V
V out + 1.23 1.0 )
R2 + R1
= 25 V
= 2.5 A
V out
V
ref
* 1.0
Example
R2
R1
in
)
+ 1.8 k
Select R1 = 1.8 kW
1.23 V
8.0 V
* 1.0