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PDF ( 数据手册 , 数据表 ) BD9421F

零件编号 BD9421F
描述 LED Drivers
制造商 ROHM Semiconductor
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BD9421F 数据手册, 描述, 功能
Datasheet
LED Drivers for LCD Backlights
White LED Driver for large LCD Panels
(DCDC Converter Type)
BD9421F
General Description
BD9421F is high efficiency driver for white LED. This is
designed for large sized LCD. BD9421F is built-in
DCDC converters that supply appropriate voltage for
light source.
BD9421F is also built-in protection function for
abnormal state such as OVP: over voltage protection,
OCP: over current limit protection of DCDC, SCP: short
circuit protection, open detection of LED string.
Thus this is used for conditions of large output voltage
and load conditions.
Features
6ch LED constant current driver(External PNP Tr
Type)
Maximum LED setting current 500mA(VREF Pin
setting)
±2% LED current accuracy(VREF=0.9V setting)
Built-in DC/DC converter
Analog Dimming(Linear) function
LED protection function(OPEN/SHORT
protection)[PWM-independent Type]
Individual detection and individual LED OFF for both
OPEN and SHORT circuit
VOUT Over Voltage Protection(OVP) and reduced
voltage protection(SCP) circuit
Built-in under voltage lockout function(UVLO) and
over voltage protection(OVP)
Built-in VOUT discharge circuit while shutdown
Key Specifications
VCC Supply Voltage Range:
9.0V to 35.0V
DCDC Oscillation Frequency: 150kHz(RT=100k)
Operation Circuit Current:
5mA(Typ)
Operating Temperature Range: -40°C to +85°C
Applications
LED driver for TV, Monitor and LCD Back Light
Package
SOP24
W(Typ) x D(Typ) x H(Max)
15.00mm x 7.80mm x 2.01mm
Pin Pitch 1.27mm
Figure 1. SOP24
Typical Application Circuit
Figure 2. Typical Application Circuit
Product structure : Silicon monolithic integrated circuit
.www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 14 • 001
This product has no designed protection against radioactive rays
1/27
TSZ02201-0F1F0C100310-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com







BD9421F pdf, 数据表
BD9421F
Datasheet
Description of pin function
P in 1: REG75
The REG pin is used in the DC/DC converter driver block to output 7.5V power. The maximum operating current is 10mA.
Using the REG pin at a current higher than 10mA can affect the N pin output pulse, causing the IC to malfunction and
leading to heat generation of the IC itself. To avoid this problem, it is recommended to make load setting to the minimum
level.
Pin 2:N
The N pin is used to output power to the external NMOS gate driver for the DC/DC converter in the amplitude range of
approx. 0 to 7.5V. Frequency setting can be made with a resistor connected to the RT pin. For details of frequency
setting, refer to the description of the RT pin.
Pin 3: PGND
The PGND pin is a power ground pin for the driver block of the N output pin.
Pin 4: CS
CS pin is current detect for DC/DC current mode inductor current control pin.
Current flowing through the inductor is converted into voltage by the current sensing resistor RCS connected to the CS
pin and this voltage is compared with voltage set with the error amplifier to control the DC/DC output voltage.
The CS pin also incorporates the overcurrent protection (OCP) function. If the CS pin voltage reaches 0.4V (Typ.) or
more, switching operation will be forcedly stopped.
Pin 5: FB
Current mode control DC/DC converter error amplifier output pin. By monitoring voltage of BS16pin, the highest Vf of
LED column will set 2/3(typ.) of applied VREF voltage to BS pin voltage to control inductor current.
The phase compensation setting has described separately.
In addition, PWM pin will become High Impedance when all PWM signals are in low state, and will maintain FB voltage.
Pin 6: VREF
LED current setting pin.1/3(typ) of applied voltage to VREF pin will be LED current
feedback voltage, 2/3(typ.) of its voltage will be DCDC feedback voltagethe
lowest BSx pin feedback voltage.
Basically, because high accuracy of resistor divider is inputted to VREF pin
externally, the IC internally will be OPENHigh Impedancestate. Please use
external power to design it. It cannot be used in OPEN state.
Pin 7-12: BS1-BS6
LED DRIVER output pin. Please connect to Base Terminal of external PNP Tr.
Pin 13-18: CL6 – CL1
LED current detect pin. By monitoring voltage of CLx pin to detect LED current.
Please connect resistor to collector pin of external PNP Tr.
Pin 19: PWM
ON/OFF terminal of LED driver pin. It inputs PWM dimming signal directly to adjust output DUTY dimming.
High/Low level of PWM terminal is shown as follows:
State
LED ON state
LED OFF state
PWM Voltage
PWM= 1.5V~18.0V
PWM= -0.3V0.8V
Pin 20: OVP
The OVP pin is an input pin for overvoltage protection and short circuit protection of DC/DC output voltage. When voltage
of it over 3.0V or higher, CP counting start.
When OVP pin voltage<0.1V (typ.) or lower, short circuit protection (SCP) function is activated, and output of Gate driver
will become low immediately.
www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
8/27
TSZ02201-0F1F0C100310-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com







BD9421F equivalent, schematic
BD9421F
Setting example
Output=VOUT[V]=40V
LED 1ch current=120mA, total LED current IOUT[A]=120mA×6ch=0.72A
DCDC input voltage=VIN [V] =24V
DCDC efficiency=η[%]=90%
Mean input current IIN required for the whole system is given by the following equation:
Datasheet
DCDC switching frequency=fsw[Hz]=200kHz
Inductor [H]=33μH
The inductor ripple current ΔIL [A] is given by the following equation:
ΔIL
(VOUT [V ] VIN [V ]) VIN [V ]
L[H ] VOUT [V ] f SW [Hz ]
 
(40[V ] 24[V ]) 24[V ]
33 10 6 [H ] 40[V ] 200 10 3[Hz ]
1.45
[ A]
As a result, the peak current Ipeak of IL is given by the following equation.
When RCS resistance is set to 0.1ohm, the VCS peak voltage will be given by the following equation:
Consequently, the result meets the condition.
Furthermore, IOCP current at which OCP is detected is given by the following equation:
I OCP
0.4[V ]
0.1[]
4.0
[ A]
So must select the component of about 5A in order to meet the above result.
I peak I OCP Max. Current tolerance for component
Particularly, To select DC/DC components, give consideration to IC variations as well as individual component
variations, and then conduct thorough verification on practical systems..
The lower limit value of coil ripple current Imin is given by the following equation, the component will not be put into
discontinuous mode.
I min I IN [ A]
IL[ A] [ A] 1.33[ A] 0.73[ A] 0.60[A] 0
2
For the selection of DC/DC components, please also consider the inaccuracy of each componentts.
www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
16/27
TSZ02201-0F1F0C100310-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com










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