BD9202EFS 데이터 시트보기 (PDF) - ROHM Semiconductor

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BD9202EFS

White backlight LED drivers

ROHM Semiconductor 

BD9202EFS

Technical Note

○Booster DC/DC Controller

・ LED Series Numeric

It detects the LED cathode voltage, or the LED voltage, and controls the output voltage to be 0.75 (Typ.). The booster only

operates when the LED output is operating. When multiple LED outputs are operating, the LED VF controls the LED output

of the highest line to be 0.75V (Typ.). Therefore, the voltages of other LED outputs are higher by the variation of VF.

Furthermore, you must be aware that the LED inline numerics have the following limits. At open detection, 85% of

the OVP configured voltage becomes the trigger, so the maximum value of output voltage during normal operation is

51V=60×0.85, and 51V/VF>maximum N.

・ Over voltage Protection Circuit OVP

Inputs the output voltage to the OVP terminal with resistive divide. The configured value of OVP should be

determined by the series numeric of the LED and the VF variance. When determining the OVP configured voltage,

the open detection trigger, OVP×0.85 should be considered. The switching operation stops when OVP is detected.

Furthermore, if the output voltage falls to 80% of the OVP configuration voltage within the filter time tcp1 determined

by CP1, OVP is released. If OVP continues for over tcp1, the error detection flag FAIL1 turns to Low, it latches with

the switching operation in the stopped position.

When the output voltage side is ROVP1 and the GND side is ROVP2, the OVP detection voltage is:

VOVP=(ROVP1+ROVP2)/ROVP2×2.0V

When ROVP1=560kΩand ROVP2=20kΩ, OVP activates when VOUT=58V or more.

・ Booster DC/DC Converter Oscillation Frequency and LED Driver PWM Standard Frequency

By attaching resistance to RT (BRT), it is possible to configure triangular wave oscillation frequency. The RT (BRT)

determines the charge and discharge current corresponding to the internal condenser, and the frequency changes.

Configure the RT (BRT) resistance by referring to the theoretical formula below. We recommend a range of 30kΩ

~300kΩ. Configurations outside of the frequency range in the chart below can result in stopping switching, and

operation cannot be guaranteed.

RTR(BTR( BT)R-FTO) -SFCOCShCa特rac性teristics

1200

1000

800

Calculated

600

(A計ctVu算aallu値Leine)

(実線）

400

実M測ea値sured

( マ ーVカaーlue）

(Marker)

200

fosc  3.04  104 [kHz]

RT (BRT )[kΩ]

0

0

100

200

300

400

500

600

RT(BRT)[kΩ]

・ Internal Oscillation Frequency Output Terminal CT_SYNC_OUT and External Synchronous Terminal CT_SYNC_IN

The internal oscillation frequency output terminal CT_SYNC_ OUT outputs the internal oscillator’s clock configured by the

RT terminal. However, there is no output when there is a CLK input in the external synchronous terminal CT_SYNC_IN.

The external synchronous terminal CT_SYNC_IN can be the operational frequency of the DC/DC converter by

externally inputting CLK. At this time, the external input frequency should be configured to be higher than the internal

oscillation frequency. Furthermore, there should be no switching between the external synchronous and internal oscillator

during operation.

・ Soft Start

There is no soft start function with this IC. At startup, stand-up occurs with control by the current value configured by

OCP (over-current detection).

・ Over-current Protection Circuit (OCP)

The current flowing through the coil is changed to voltage by the sense resistance Rcs, and when the CS terminal is

over 0.2V (typ), the switching operation is stopped.

OCP detection is in pulse-by-pulse format, and is detected at every switching cycle and reset at the next clock.

When detection continues longer than the time configured at tCP1, FAIL1=L and it latches with the switching operation

in the stopped position.

○ Error Detection Output Function

・ Outputs errors detected by protection circuits to FAIL1 and FAIL2 terminals. FAIL1 or FAIL2 switch to Low after the

filter time configured at CP1 or CP2, when they detect OVP or OCP (FAIL1) or LED open/short (FAIL2). (Because

FAIL1 terminal is open collector output, it is used with external pull-up.)

The filter time for CP1 and CP2 is expressed as:

Tcp1(cp2)  Ccp1 2V

1μA

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© 2009 ROHM Co., Ltd. All rights reserved.

11/19

2009.04 - Rev.A

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