BD9486F 데이터 시트보기 (PDF) - ROHM Semiconductor

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BD9486F

1ch Boost up type White LED Driver for large LCD

ROHM Semiconductor 

BD9486F

○Pin 13: DIMOUT

This is the output pin for external dimming NMOS. The table below shows the rough output

logic of each operation state, and the output H level is VCC. Please refer to “3.5 Timing Chart”

for detailed explanations, because DIMOUT logic has an exceptional behavior. Please insert

the resistor RDIM between the dimming MOS gate to improve the over shoot of LED current, as

PWM turns from low to high.

Status

Normal

Abnormal

DIMOUT output

Same logic to PWM

GND Level

Datasheet

Figure 15. DIMOUT terminal circuit example

○Pin 14: GATE

This is the output terminal for driving the gate of the boost MOSFET. The high level is VCC. Frequency can be set by the

resistor connected to RT. Refer to <RT> pin description for the frequency setting.

○Pin 15: CS

The CS pin has two functions.

1. DC / DC current mode Feedback terminal

The inductor current is converted to the CS pin voltage by the sense resistor

RCS. This voltage compared to the voltage set by error amplifier controls the

output pulse.

2. Inductor current limit (OCP) terminal

The CS terminal also has an over current protection (OCP). If the voltage is

more than 0.4V(typ.), the switching operation will be stopped compulsorily. And

the next boost pulse will be restarted to normal frequency.

In addition, the CS voltage is more than 1.0V(typ.) during four GATE clocks, IC

will be latch off. As above OCP operation, if the current continues to flow

nevertheless GATE=L because of the destruction of the boost MOS, IC will

stops the operation completely.

Both of the above functions are enabled after 300ns (typ) when GATE pin Figure 16. CS terminal circuit example

asserts high, because the Leading Edge Blanking function (LEB) is included

into this IC to prevent the effect of noise.

Please refer to section “3.3.1 OCP Setting / Calculation Method for the Current Rating of DCDC Parts”, for detailed

explanation.

If the capacitance Cs in the right figure is increased to a micro order, please be careful that the limited value of NMOS

drain current Id is more than the simple calculation. Because the current Id flows not only through Rcs but also through

Cs, as the CS pin voltage moves according to Id.

○Pin 16: VCC

This is the power supply pin of the IC. Input range is from 9V to 18V.

The operation starts at more than 7.5V(typ) and shuts down at less than 7.2V(typ)

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