BD9428 Datasheet, PDF (9/29 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter type)

BD9428
Datasheet
●Pin Functions
VCC
The VCC pin is used to supply power for the IC in the range of 9 to 35V.
If the VCC pin voltage reaches 7.5V (Typ.) or more, the IC will initiate operation. If it reaches 7.2V (Typ.) or less, the IC
will be shut down.
REG100
The REG100 pin is used in the DC/DC converter driver block to output 10V power. The maximum operating current is
15mA. Using the REG100 pin at a current higher than 15mA 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. The characteristic of VCC line regulation at REG100 is shown as Figure 7. (page.8). VCC must be
used in more than 12V (Io=0mA), 14V (Io=15mA) for stable 10V output, respectively.
Please place the ceramic capacitor connected to REG100 pin (2.2uF~10uF) closest to REG100-GND pin.
CS
The CS pin has the following two functions:
1. DC/DC current mode current feedback function
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.
2. Inductor current limit function
The CS pin also incorporates the over current protection (OCP) function. If the CS pin voltage reaches 0.45V (Typ.) or
more, switching operation will be forcedly stopped.
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 REG100. ON resistances is 5Ω (Typ.) in source (H side), 3Ω (Typ.) in sink (L side).
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.
GND
Ground of the IC.
LED1 – LED4
The LED1 to 4 pins are used to output constant current to LED drivers. Current value setting can be made by connecting
a resistor to the ISET pin.
For the current value setting procedure, refer to the description of “ISET pin”.
If any of the LED pins is put in an erroneous state (e.g. short circuit mode, open circuit mode, or ground short circuit
mode), the relevant protection function will be activated.
This IC is detected automatically that it is an unused channel by asssuming the LED terminal to be connected to GND
before start up.
PWM
The PWM pin is used to turn ON and OFF LED drivers. Light can be modulated by changing the duty cycle through the
direct input of a PWM light modulation signal
The high and low voltage levels of PWM pin is as listed in the table below:
State
LED ON
LED OFF
PWM Voltage
PWM= 2.0V to 35V
PWM= －0.3V to 0.8V
ISET
The ISET pin is an output current setting resistor. Output current ILED varies in inverse proportion to resistance.
The relation between output current ILED and the resistance of ISET pin connection resistor RISET is given
by the following equation:
I _LED [mA]

7500
R_ISET [kΩ]
Output current setting should be made in the range of 30 to 250mA.
When it reaches under VISET×0.90V(typ), the LED current is off to prevent from passing a large current to the LED pin
when the RISET is shorted and the ISET pin is shorted to the GND. And as the ISET pin returns to a normal state, the
LED current returns.
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TSZ02201-0F1F0C100290-1-2
16.Oct.2013 Rev.001