BD9470AEFV Datasheet, PDF (12/39 Pages) Rohm – White LED driver for medium sized and large sized LCD back light

BD9470AFM・BD9470AEFV
○STB (HTSSOP-B28:27PIN / HSOP-M28：20PIN）
The pin is used to ON/OFF the IC and allowed for use to reset the IC from shutdown.
The IC state is switched between ON and OFF state according to voltages input in the STB pin. Avoid using the STB pin
between two states (0.8 to 2.0V).
Input sequence of STB/PWM for startup, please input PWM before STB or at the same timing.
While in shutdown mode, the timer keeps counting until the IC is completely shut down. For details of shutdown operation,
refer to information in’3.1 application explanation/ the setting of REG58 capacity and shutdown procedure'
○VCC （HTSSOP-B28:28PIN / HSOP-M28：21PIN）
IC power supply pin. Input range is 9~35V.
VCC pin voltage reaches 7.5V (Typ.) or more, the IC will initiate operation. If it reaches 7.2V (Typ.) or less, IC will be shut
down.
○REG58 （HTSSOP-B28:1PIN / HSOP-M28：22PIN）
The REG pin is used in the DC/DC converter driver block to output 5.8V voltage. The maximum operating current is
15mA.Using the REG 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.
In addition, The REG58 pin is also allowed for use as discharge timer for DC/DC output capacitance.
For details, refer to information in ’3.1 application explanation/ the setting of REG58 capacity and shutdown procedure'
○CS （HTSSOP-B28:2PIN / HSOP-M28：23PIN）
The CS pin has the following two functions.
１．DC/DC current mode current feed Back function
Current flowing through the inductor is converted into voltage by the current sensing resistor RCS which connected to 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 (OCP pin)
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.
For detailed explanation, Please refer to information in “3.2 Selection of DC/DC Components-OCP setting procedure /
DC/DC component current tolerance selection procedure”.
○N （HTSSOP-B28:3PIN / HSOP-M28：24PIN）
The N pin is used to output power to the external NMOS gate driver for the DC/DC converter in the amplitude range of
approximately 0 to 5.8V.Frequency setting can be adjusted by a resistor connected to the RT pin. For details of frequency
setting, refer to the description of the RT pin.
○DCDC_GND （HTSSOP-B28:4PIN / HSOP-M28：25PIN）
The DCDC_GND pin is a power ground pin for the driver block of the output pin N.
○RT （HTSSOP-B28:5PIN / HSOP-M28：26PIN）
The RT pin is used to connect a DC/DC frequency setting resistor. DC/DC drive frequency is determined by connecting the
RT resistor.
・Relationship between Drive frequency and RT resistance (Ideal)
R_RT
=
15000
f _SW [kHz]
[kΩ]　
However, drive frequency setting is limited in the range of 100 kHz to 500kHz.
For calculation, refer to information in ’3.1 application explanation/ DC/DC converter drive frequency setting’
When it reaches under VRT×0.90V(typ), DCDC operation will be stopped in order to prevent from high speed oscillation
when the RT resistance is shorted to GND. And when RT pin returns to normal state, DCDC also returns to operation.
○FB （HTSSOP-B28:6PIN / HSOP-M28：27PIN）
The FB pin is an output of DC/DC current mode error amplifier. FB pin detects the voltages of LED pins (1 to 6) and
controls inductor current so that the pin voltage of the LED located in the row with the highest Vf will come to 0.45V(130mA,
typ.). Therefore, the pin voltages of other LEDs will become higher by Vf variation.
FB Voltage keep internal IC with PWM=Low timing, and it can hold by using copied FB voltage while PWM=Low.（The FB
keep voltage range is 0~4V, 40steps）
For setting example, refer to information in ’3.1 application explanation/ the necessity for holding output voltage and FB
voltage while PWM=Low’
○SS （HTSSOP-B28:7PIN / HSOP-M28：28PIN）
Soft start time and duty for soft start setting pin. The SS pin normally sources 2.0uA (Typ.) of current.
The IC has a built-in soft start start-up 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. When the SS pin voltage reaches 3.7V
(Typ.), soft start operation will be completed to unmask the LED protection function.
For setting example, refer to information in ’3.1 application explanation/ start-up and SS capacity setting explanation’
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TSZ22111・15・001
12/35
TSZ02201-0F10C1002000-1-2
19.Oct.2013 Rev.003