BD9420F Datasheet, PDF (8/31 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter Type)

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= -0.3V～0.8V
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 BS（1～6）pin, 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 0.3V～2.5V.
 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 voltage（the
lowest BSx pin feedback voltage）.
Basically, because high accuracy of resistor divider is inputted to VREF pin
externally, the IC internally will be OPEN（High Impedance）state. 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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TSZ02201-0F1F0C100300-1-2
31.Jan.2014 Rev.002