BD9202EFS データシートの表示（PDF） - ROHM Semiconductor

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BD9202EFS

White backlight LED drivers

ROHM Semiconductor 

BD9202EFS

Technical Note

【Protection Functions】

Protection Function

Detection

Release

UVLO (VREG)

VREG＜2.9V

UVLO (EXT)

UVLO＜1.9V

TSD

Tj＞175℃

OVP

VOVP＞2.0V &

t>tCP1

OCP

VCS≧0.2V &

t>tCP1

LED open detection

VLED＜0.2V &

VOVP＞1.7V

LED short detection

VLED≧4.0V

To clear the latch type, the logic section must be reset.

VREG＞3.0V

UVLO＞2.0V

Tj＜150℃

VOVP＜1.5V

VCS＜0.2V

VLED＞0.2V &

VOVP＜1.6V

VLED＜4.0V

Type

Hysteresis

Hysteresis

Hysteresis

Latch

Latch

Latch

Latch

Logic at detection

FAIL1 FAIL2

H

H

H

H

H

H

L

H

L

H

H

L

H

L

Protection Function

UVLO (VREG)

UVLO (EXT)

TSD

OVP

OCP

LED open detection *1

LED short detection *1

DCDC

Stop

Stop

Stop

Stop

Current limit

Stop

Stop

Operation at protection function detection

LOADSW

LED Dr

ON

All CH stop

ON

All CH stop

ON

All CH stop

OFF

(All CH stop) *2

OFF

Normal operation

ON

All CH stop

ON

All CH stop

Internal logic

Reset

Reset

Reset

Normal operation

Normal operation

Normal operation

Normal operation

*1 LED open and short detection is only valid with operating channels, and all CH turn to OFF when 1-ch error is

detected. Furthermore, it is only valid in the ON areas during PWM operation.

*2 Because the DC/DC converter stops and there is no voltage supply for the LED, the light will be turned off.

● Selection of External Parts

1. Selection of Coil (L)

ΔIL

VCC

L

IL

VOUT

CO

The value of the coil greatly affects the input ripple current. As presented

in formula (1), the larger the coil and the higher the switching frequency, the

lower the ripple current.

ΔIL



(VOUTVcc)  Vcc

L VOUT ｆ

　[ A]　　　　・・・・・　　(1)

When efficiency is expressed as in formula (2), the input peak current is as

shown in formula (3).





VOUT

Vcc

IOUT

Icc

　　　　　・・・・・　　(2)

ILMAX



Icc 

ΔIL

2



VOUT IOUT

Vcc

　　 　　ΔIL

2

　・・・・・　　(3)

※ If current that is stronger than the coil’s fixed current value flows through the coil, there is magnetic saturation in

the coil, lowering efficiency.

A margin large enough should be considered during selection, so that the peak current does not exceed the coil’s

fixed current value.

※ To lessen loss from the coil and improve efficiency, coils with low resistance components (DCR and ACR) should

be selected.

2. Selection of Output Condenser (Co)

The stability domain of the output voltage and equivalent series resistance necessary to smooth out the ripple voltage should be

consideredVwCChen choosing a condenser for the output side.

The output ripple voltage is determined by formula (4).

L

IL

VOUT

ΔVOUT



ILMAX 

RESR

l

Co



IOUT





1

ｆ

　[V

]　　　　・・・・・　　(4)

(ΔIL: output ripple current, ESR: equivalent series resistance of Co, η:

efficiency)

ESR

※The condenser’s fixed value should be selected with enough margin for

the output voltage.

CO

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© 2009 ROHM Co., Ltd. All rights reserved.

12/19

2009.04 - Rev.A

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