Flash Driver

LP5527 has an internal constant current driver that is ca-

pable for sinking low (50 mA) and high (400 mA) current

mainly targeted for torch and flash LED in camera phone

applications. 400 mA flash driver can be hardware or soft-

ware enabled. Flash safety function prevents hardware dam-

ages due to possible overheating when the flash has been

stuck on because of a hardware, software, or user error.

Flash safety counter starts counting when the flash is acti-

vated, and disables the flash automatically when the pre-

defined 1.0s or 2.0s time limit is reached. Flash is activated

with FLASH_SYNC bit or FLASH_SYNC pin, as defined in

the table below. Safety time limit is defined by SAFETY-

_TIME bit. (Time limit is 2.0s if SAFETY_TIME bit is low and

1.0s if the bit is high.)

Flash LED Control (X = don’t care)

EN_TORCH bit

EN_FLASH bit

FLASH_SYNC bit or pin

SAFETY_TIME bit

Flash LED Action

0

0

X

X

Off

1

0

X

X

Torch

X

1

Change from LOW to HIGH to

engage; from HIGH to LOW to

disengage

0 for 2.0 seconds;

1 for 1.0 second

Flash

Flash Programming Example

Address

Data

Function

00H

8FH

Sets safety time to 1.0s. In this example LED1 to LED4 are enabled.

00H

9FH

Enables torch.

00H

FFH

Activates FLASH. EN_FLASH bit and FLASH_SYNC bit are written simultaneously because EN_FLASH

disables torch.

00H

BFH

Disables FLASH. If FLASH is disabled by safety time, FLASH_SYNC bit needs to be written to 0 before

next FLASH.

FLASH DRIVER ELECTRICAL CHARACTERISTICS

Limits in standard typeface are for T

=10µF, C

= 1200

Ω

Symbol

Parameter

Condition

Min

Typ

Max

Units

I

MAX

Maximum Sink Current

3.0V

≤ V

IN

≤ 5.5V, V

370

(-7,5%)

400

430

(+7,5%)

mA

I

TORCH

Torch Mode Sink Current 3.0V

≤ V

IN

≤ 5.5V

50

mA

I

LEAKAGE

Flash Driver Leakage

Current

V

0.1

µA

t

FLASH

Flash Turn-On Time

(Note 11)

20

µs

V

SAT

Saturation Voltage

3.0V

≤V

IN

≤ 5.5V, Current Decreased to

95% of the Maximum Sink Current

550

mV

t

SAFETY

Safety Time Accuracy

-9

+9

%

Note 11: Flash turn-on time is measured from the moment the flash is activated until the flash current crosses 90% of its target value.

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