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●5V constant voltage（VREG）

5V (Typ.) is generated from VCC input voltage when EN=H. This voltage is used as a power supply of the internal circuit, and

also when the device pins need to be fixed to H voltage.

UVLO is built-in in VREG, and the circuit begins to operate when the voltage is more than 2.9V (Typ.) and stops when the

voltage is less than 2.8V (Typ.).

Please connect Creg=10uF (Typ.) to VREG terminal for phase compensation. The circuit’s operation becomes remarkably

unstable when Creg is not connected.

● Self-diagnosis function

The operating condition of the built-in protection circuit is transmitted to FAIL1 and FAIL2 output pins (open drain).

When UVLO, OVP, OCP or TSD is operated, FAIL1 output becomes L SWOUT is fixed to L, and the step-up conversion is

stopped. For OCP, SWOUT is fixed to L for only 1 cycle of FOSC because of the pulse-to-pulse mode operation. For UVLO,

OVP, TSD operations, LED output pins become open (Hi-Z）. When FAIL1 becomes L, LOADSW is turned off as they are

inverted to each other.

FAIL2 output becomes L when open or short is detected. The open/short detection is a latch mode, and the latch is released by

ON/OFF (UVLO) of EN. The device judges as open when LED output is lower than 0.15V (Typ.) as well as when the voltage of

OVP terminal reaches 1.7V (Typ.). The short is detected when LED output becomes more than 4.5V (Typ.). Therefore, there is

a possible scenario that short detection cannot be carried out if the difference between LED terminal voltage at the time of

being normal and LED terminal voltage at the time of being abnormal is less than 3.7V (4.5V-0.8V) (Typ.). As for short

detection hereon, if one LED in some column of LED output, for example, becomes short mode, and is in the status of nothing

but VF being low, then cathode voltage is in the status of nothing but VF being high. LED short detection and OCP are

separate protection circuits. Please take care because short detection is masked as soon as open/short is detected. However,

the open detection operates. An additional capacitance added to LED output slows down the operation and the short may be

detected.

For the two FAIL output pins, add pull-up resistors for each as they are open drain.

● Constant-current driver

Please turn off the output with LEDEN if there is constant-current driver output that is not used. The truth-table is shown below.

If constant-current driver output that is not used is not treated with LEDEN but is made open, then the open detection will

operate. Also, please do not short the driver output to GND as the inputs of the error amplifier cannot be deactivated with

LEDEN. Instead keep the driver output to open or short it to VREG.

LED EN

LED

〈

1〉

〈

2〉

1

2

3

4

L

L

ON

ON

ON

ON

H

L

ON

ON

ON

OFF

L

H

ON

ON

OFF

OFF

H

H

ON

OFF

OFF

OFF

OVP

OCP

TSD

UVLO

FAIL1

OPEN

SHORT

FAIL2

S Q

R

EN=OFF

(UVLO)

MASK

LED1

0.15V

GND

0.8V

Other LED output

4.5V

0.8V

Step-up voltage VOUT

VFxN+0.8V

OVP

1.7V

2.0V

LED1

Open

LED1

Off

Short detection is not turned off

because it is masked.

FAIL2