BD9421F_15 Datasheet, PDF (8/31 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter Type)

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 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 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 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 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. CLx pin of no use channel set CLx>3.3V.
 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= -0.3V～0.8V
 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.
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TSZ02201-0F1F0C100310-1-2
25.Sep.2015 Rev.003