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11 -

Soft step-up

The operation becomes soft step-up by charge pump operation right after 2x mode starts. Rush current is

decreased by soft step-up which increases Vo straight. The current is controlled when Iled becomes 1/2 of

the setting during soft step-up. Iled is limited under 350mA(typ.) forcibly to avoid abrupt change of Iled

within 10us after step-up operation starts. Iled control current returns to the setting after step-up is finished.

2x mode

After switching to normal 2x mode, operation remains this mode until standby mode(EN1=EN2=GND)

starts. To work under 1x mode again, it is necessary to restart after switching to standby mode.

■Protection function

Thermal protection

When junction temperature becomes over 150°C, Vo output is turned to be OFF (only high resistance

PMOS switch is ON)thermal shutdown circuit and LED output is shut down by thermal shutdown circuit.

To shut down thermal protection, it is necessary to restart operation after returning to standby mode.

ISET1/ISET2 short protection

When EN1=0→1 during start-up, if Rset which is connected to ISET1 is under 3.9kΩ(setting current of

Iled is above 1A),LED current which is the same with[low] current is shut down. If ISET2 is under normal

operation under this situation, LED current which is the same with[high] current is flowed. When it is short

between ISET1 and GND under the operation that EN1=1, LED current limit is detected by 1.5A and shut

down without flowing to EN logic.

When EN2=0→1 during start-up, if Rset which is connected to ISET2 is under 3.9kΩ( setting current of

Iled is above 1A), LED current which is the same with[high] current is shut down. If ISET1 is under nor-

mal operation under this situation, LED current which is the same with[low] current is flowed. When it is

short between ISET2 and GND under the operation that EN2=1, LED current limit is detected by 1.5A and

shut down without flowing to EN logic.

LED current becomes 0 when [low]+[high]current reaches 1.5A under EN1=EN2=1 under the above-men-

tioned 2 situations.

VO short protection

When VO lowers to around 0.7V during operation, device shuts down the outputs of both Vo and LED; Vin

and Vo become connected by high resistance PMOS switch(standby output) under this situation. After VO

short is dissolved and Vo rises above 0.7V, outputs of Vo and LED restart. When VO short is detected un-

der 2x mode, the operation switches to standby mode.

Fail safe function

Fail safe function refers to the function that the output of LED is turned to be OFF automatically when

“low+high” current(EN1=EN2=1) continues for certain period of time. To dissolve the function that LED

output is turned to be OFF forcibly, it is necessary to switch EN1=EN2=1 to other modes. 3 options are

available for FS time; FS time is set by external resistors (Rfs). This function can be turned off by setting

short between FS and VIN pins or FS to be open.