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PDF ( 数据手册 , 数据表 ) BD9420F

零件编号 BD9420F
描述 LED Drivers
制造商 ROHM Semiconductor
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BD9420F 数据手册, 描述, 功能
Datasheet
LED Drivers for LCD Backlights
White LED Driver for large LCD Panels
(DCDC Converter Type)
BD9420F
General Description
BD9420F is high efficiency driver for white LED. This is
designed for large sized LCD. BD9420F is built-in
DCDC converter that supply appropriate voltage for
light source.
BD9420F 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
Built-in PWM-independent soft start circuit
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
SOP28
W(Typ) x D(Typ) x H(Max)
18.50mm x 9.90mm x 2.41mm
Pin Pitch 1.27mm
Figure 1. SOP28
Typical Application Circuit
Figure 2. Typical Application Circuit
Product structure : Silicon monolithic integrated circuit This product has no designed protection against radioactive rays
.www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
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BD9420F pdf, 数据表
BD9420F
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: SEL
SEL pin is PWM control select pin. The PWM control mode is switched according to voltages input in the SEL pin. Avoid
using the SEL pin between two states (0.8 to 1.5V).
SEL Voltage
SEL= 1.5V~18.0V
SEL= -0.3V0.8V
State
PWMA CH1,CH2 common mode control
PWMB CH3,CH4 common mode control
PWMC CH5,CH6 common mode control
PWMA CH1,CH2,CH3 common mode control
PWMB no use
PWMC CH4,CH5,CH6 common mode control
Pin 6: 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 7: LSP
LED Short detect voltage setting pin. When LSP=OPEN, LSP pin voltage is 0.9V( typ), the BSx pin of LED SHORT
detect voltage is set to 9V.
The 10 times of LSP pin voltage is the BSx pin LED SHORT protection detect voltage.
Please set LSP pin input voltage range from 0.3V2.5V.
Pin 8: 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 9-14: BS1-BS6
LED DRIVER output pin. Please connect to Base Terminal of external PNP Tr.
Pin 15-20: 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.
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© 2013 ROHM Co., Ltd. All rights reserved.
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TSZ02201-0F1F0C100300-1-2
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BD9420F equivalent, schematic
BD9420F
Datasheet
Selection of DC/DC Components
OCP setting / DCDC component current tolerance selection guide
The OCP detection function that is one of the functions of the CS pin will stop the DC/DC converter operating if the CS
pin voltage becomes larger than 0.4V.Consequently, it is needed to calculate a peak current flowing through the coil L and
then review the resistance of RCS. Furthermore, a current tolerance for DC/DC components should be larger than that for
peak current flowing through the coil L. The following describes the peak coil current calculation procedure, CS pin
connection resistor RCS selection procedure, and DC/DC component current tolerance selection procedure .
Peak coil current Ipeak calculation
Ripple voltage generated at the CS pin is determined by conditions
L VOUT
for DC/DC application components first, Assuming the conditions as
below:
VIN
output voltage=VOUT[V]
IL
LED total current=IOUT[A]
DCDC input voltage=VIN[V]
fsw
DCDC efficiency=η[%]
N
And then mean input current IIN required for the whole system is given
by the following equation.
I IN
VOUT [V ]IOUT [ A]
VIN [V ][%]
[ A] 
CS
PGND
Rcs
Further, according to drive operation with the DC/DC converter switching
frequency fsw [Hz], inductor ripple current ΔIL [A] generated at the inductor L (or
H) is given by the following equation.
ΔIL (VOUT [V ] VIN [V ]) VIN [V ] [ A]
L[H ] VOUT [V ] f SW [Hz ]
As a result, the peak current Ipeak of IL is given by the following equation.
Ipeak
I IN [ A]
IL[ A]
2
[ A](1)
CS pin connection resistor RCS selection procedure
The current Ipeak flows into RCS to generate voltage.See the timing
chart shown to the rightThe voltage VCSpeak is given by the following
equation.
VCS peak Rcs Ipeak [V ]
If VCSpeak voltage reaches 0.4V, DC/DC output will stop.Consequently,
to select RCS resistance, the following condition should be met.
Rcs Ipeak [V ] 0.4[V ]
DC/DC component current tolerance selection procedure
Iocp current needed for OCP detection voltage CS to reach 0.4V is given
by the following equation:
I OCP
0.4[V ]
Rcs[]
[ A](2)
The relation among Ipeak current (Equation (1)), Iocp current (Equation (2)), and Maximum current tolerance for
component should meet the following equation.
I peak I OCP MAX current tolerance
DC/DC application components including FETs, inductors, and diodes should be selected so that the Equation
shown above will be met.
In addition, it is recommended to use continuous mode in DCDC application. And the lower limit value of coil ripples
current Imin so as to meet the following equation:
I min
I IN [ A]
IL[ A] [ A]
2
0
A failure to meet this condition is referred to as discontinuous mode and this failure may result in an inadequate rise in
output voltage.
www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
16/28
TSZ02201-0F1F0C100300-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com










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