BD63536FJ Просмотр технического описания (PDF) - ROHM Semiconductor

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BD63536FJ

Step-down,High-frequency Switching Regulator (Controller type)

ROHM Semiconductor 

BD63536FJ

Typical application design

The following section shows a typical application design.

VREF

VREG

R

OSC

C

OSC

1.25v

Soft Start

GATEOFF、OVP

TSD、UVLO

IN-

UVLO

TSD

OVP

COMP

C.L.

COMP

GATE

OFF

Controller

FB

GND

Vcc

CS

GATE

Technical Note

VIN

Rfb1

Rfb2

Fig.20 Typical application design

Example of simple design

The following section shows a design example of constants targeting the applications listed below.

Power supply voltage24V, Output voltage3.3V, Coil47µF, Output capacitor2200µF, Resr0.015, PWM frequency80

kHz, and Load resistance10

1. Determination of values of output voltage detecting resistance

The internal reference voltage is 1.25V and the maximum IN-bias current is 2µA. Consequently, to output Vout of 3.3V,

select resistance values enough to keep from the influence of this bias current, that is, Rfb133k and Rfb220k. In

this case, the ratio of Rfb1 to Rfb2 cannot be changed, but the number of digits of resistance values can be changed.

2. Setting of R (resistance) and C (capacitance) used to make PWM frequency setting

When setting C to 1000pF and R to 39k, the PWM frequency will come to approximately 80 kHz.

3. Determination of L (inductance) and C (capacitance) in accordance with characteristic requirements

This design example is based on L47µF, C2200µF, and Resr0.015.

Reference

Determine a value for the coil to the extent that the system does not enter intermittent mode until it reaches the minimum

value of the preset output current. In this case, however, careful attention should be paid not to cause the coil to become

saturated when the maximum current flows.

Reference formula: L=(Vi-Vo)VoT/ΔILVi [H],

where IL  Ripple current of coil, T  1/Switching frequency

Determine a value for the output capacitor from ESR and output ripple voltage. It is recommended to use a capacity

taking into account enough margin to a value meeting the specification.

Reference formula: ΔVout  ΔIL×Resr,

where Resr  Equivalent series resistance of capacitor

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2009.11 - Rev.A

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