lp55271tlx National Semiconductor Corporation, lp55271tlx Datasheet - Page 11

• Manufacturer Part Number: lp55271tlx
• Description: Tiny Led Driver For Camera Flash And 4 Leds With I2c Programmability, Connectivity Test And Audio Synchronization
• Manufacturer: National Semiconductor Corporation

Flash Driver
LP55271 has an internal constant current driver that is ca-
pable for sinking low (46 mA) and high (370 mA) current
mainly targeted for torch and flash LED in camera phone
applications. 370 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-
Flash LED Control (X = don’t care)
Flash Programming Example
FLASH DRIVER ELECTRICAL CHARACTERISTICS
Limits in standard typeface are for T
= 10 µF, C
= 1300Ω
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.
<
Address
00H
00H
00H
00H
Symbol
I
I
I
t
V
t
T
FLASH
TORCH
LEAKAGE
FLASH
SAFETY
EN_TORCH bit
SAT
A
<
+85
X
0
1
OUT2
Data
8FH
9FH
FFH
BFH
o
C). Unless otherwise noted, specifications apply to the LP55271 Block Diagram with: V
= 10 µF, C
Parameter
Flash Mode Sink Current
(Note 8)
Torch Mode Sink Current
(Note 8)
Flash Driver Leakage Current
Flash Turn-On Time
(Note 11)
Saturation Voltage
Safety Time Accuracy
Function
Sets safety time to 1.0s. In this example LED1 to LED4 are enabled.
Enables torch.
Activates FLASH. EN_FLASH bit and FLASH_SYNC bit are written simultaneously because EN_FLASH
disables torch.
Disables FLASH. If FLASH is disabled by safety time, FLASH_SYNC bit needs to be written to 0 before
next FLASH.
EN_FLASH bit
VDDIO
0
0
1
= 100 nF, C
J
= 25
o
C. Limits in boldface type apply over the operating ambient temperature range (-30
engage; from HIGH to LOW to
Change from LOW to HIGH to
VREF
FLASH_SYNC bit or pin
= 100 nF, C
Condition
3.0V ≤ V
V
3.0V ≤ V
V
3.0V ≤ V
Current Decreased to 95% of
the Maximum Sink Current
disengage
FLASH
FB
X
X
= 5.0V
= 1.0V
VDDA
IN
IN
IN
11
≤ 5.5V,
≤ 5.5V
≤ 5.5V,
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 driver currents — both torch and flash — are set with
external resistor R
and the torch current is 60/R
lower resistance value than 1200Ω.
= 4.7 µF, C
VDD1
SAFETY_TIME bit
0 for 2.0 seconds;
1 for 1.0 second
= 100 nF, C
F
Min
-7.5
-9
. The flash current is 480/R
X
X
Typ
370
46
0.1
20
550
F
VDD2
amperes. User should not use
IN
= 3.6V, C
= 100 nF, L
Flash LED Action
Max
+7.5
+9
IN
Torch
Flash
= 10 µF, C
1
Off
= 4.7 µH, R
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F
amperes
Units
mA
%
mA
µA
µs
mV
%
OUT1
o
C
F