bd9202efs ROHM Co. Ltd., bd9202efs Datasheet - Page 12

• Manufacturer Part Number: bd9202efs
• Description: White Backlight Led Drivers For Medium To Large Lcd Panels Swreg Type
• Manufacturer: ROHM Co. Ltd.

● Selection of External Parts
© 2009 ROHM Co., Ltd. All rights reserved.
BD9202EFS
www.rohm.com
1.
2.
The stability domain of the output voltage and equivalent series resistance necessary to smooth out the ripple voltage should be
considered when choosing a condenser for the output side.
【Protection Functions】
*1 LED open and short detection is only valid with operating channels, and all CH turn to OFF when 1-ch error is
*2 Because the DC/DC converter stops and there is no voltage supply for the LED, the light will be turned off.
※ If current that is stronger than the coil’s fixed current value flows through the coil, there is magnetic saturation in
※ To lessen loss from the coil and improve efficiency, coils with low resistance components (DCR and ACR) should
Selection of Coil (L)
Selection of Output Condenser (Co)
To clear the latch type, the logic section must be reset.
detected. Furthermore, it is only valid in the ON areas during PWM operation.
the coil, lowering efficiency.
A margin large enough should be considered during selection, so that the peak current does not exceed the coil’s
be selected.
fixed current value.
L
LED open detection *1
LED short detection *1
VCC
Protection Function
L
LED open detection
LED short detection
Protection Function
VCC
I
UVLO (VREG)
L
UVLO (VREG)
UVLO (EXT)
UVLO (EXT)
I
L
OCP
OCP
TSD
OVP
TSD
OVP
ΔI
CO
L
ESR
CO
VOUT
VOUT
VOVP＞2.0V &
VLED＜0.2V &
VCS≧0.2V &
VREG＜2.9V
UVLO＜1.9V
VOVP＞1.7V
Current limit
VLED≧4.0V
Detection
Tj＞175℃
The output ripple voltage is determined by formula (4).
(ΔIL: output ripple current, ESR: equivalent series resistance of Co, η:
efficiency)
Δ
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.
When efficiency is expressed as in formula (2), the input peak current is as
※The condenser’s fixed value should be selected with enough margin for
Δ

DCDC
ILMAX
t>tCP1
t>tCP1
Stop
Stop
Stop
Stop
Stop
Stop
the output voltage.
shown in formula (3).
VOUT

IL
VOUT

Vcc
(

VOUT
12/19

Icc
L


ILMAX


IOUT
Icc
Δ
VOUT

Operation at protection function detection
2
IL
Vcc
VLED＞0.2V &
VREG＞3.0V
UVLO＞2.0V
VOVP＜1.5V
VOVP＜1.6V
VLED＜4.0V


VCS＜0.2V
LOADSW
・・・・・
Tj＜150℃
Release
)
VOUT
RESR


OFF
OFF
ON
ON
ON
ON
ON
ｆ
Vcc
Vcc


[

IOUT
A
Co

l
]
・・・・・

IOUT
(2)
Normal operation
(All CH stop) *2


All CH stop
All CH stop
All CH stop
All CH stop
All CH stop
Hysteresis
Hysteresis
Hysteresis
LED Dr

Type
Latch
Latch
Latch
Latch
Δ
1
ｆ
2
IL
[V
(1)
・・・・・
]
・・・・・
Technical Note
Logic at detection
2009.04 - Rev.A
FAIL1
Normal operation
Normal operation
Normal operation
Normal operation
Internal logic
H
H
H
H
H
L
L
Reset
Reset
Reset
(4)
(3)
FAIL2
H
H
H
H
H
L
L