BD9479FV ROHM [Rohm], BD9479FV Datasheet - Page 10

• Manufacturer Part Number: BD9479FV
• Description: White LED Driver for large LCD Panels (DCDC Converter type)
• Manufacturer: ROHM [Rohm]

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© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
BD9479FV
Pin 33 : VREF
Pin 34 : FB
Pin 35 : SS
Pin 36 : RT
Pin 37 : UVLO
Pin 38 : AGND
Pin 39 : FAIL
Pin 40 : VCC
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 hi 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.
Current mode control DC/DC converter error amplifier output pin.By monitoring
voltage of BS（1～8）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.
The SS pin is used to set the soft start time and duty for soft start duration.SS pin normally sources 2.0uA (Typ.) of
current.When STB pin become high, it wait for in any one PWMx signal from low to high.In start-up duration, SS will not
charge because all PWMx pin are in low state.
The BD9479FV has a built-in soft start startup circuit independent of PWM light modulation, and thereby raises FB
voltage as SS pin voltage rises independent of the duty cycle range of PWM light modulation.Please pay attention to
overshoot problem will occur while low duty is inputted to IC IN start-up duration.
Only a resistor connected to RT determines saw-tooth wave frequency inside IC.
When RT=100,Frequency=150kHz(typ.).
For calculation example, please refer to section in “3.2.2 – DC/DC drive frequency setting”.
GND pin for analog system inside IC.
FAIL signal indication output pin (Open Drain).In normal operation, FAIL pin is OPEN when STB=Low.When an
abnormality is detected, CP starts to charge to external capacitance and then shutdown IC while it reach 2.5V or
higher.NMOS ON is 50 ohm(typ.）when IC is shutdown.When VCC voltage is insufficient or UVLO pin voltage is lower,
FAIL pin is also in open state.
RT sets charge/discharge current determining frequency inside IC.
LED current detect pin.By monitoring voltage of CLx pin to detect LED current.Please connect resistor to collector pin of
external PNP Tr.
UVLO pin of the coil of step-up DC/DC converter and the power for external NMOSFET.
At 3.0 V (typ.) or higher, IC starts step-up operation and stops at 2.79V or lower (typ.). (It is not shutdown of IC.)
Power source pin of IC, which should be input in the range of 9 – 35 V.
Operation starts when VCC is 7.5V (TYP.) or higher and shuts down when VCC is 7.2 V (TYP.).
（Under abnormality detection）
Abnormality (shutdown),
Normal, STB=Low,
UVLO is detected
State
10/26
(50 ohm typ.)
FAIL Output
GND Level
OPEN
TSZ02201-0F1F0C100020-1-2
9.Aug.2012 Rev.001
Datasheet