AAT1270
1A Step-Up Current Regulator for Flash LEDs
If one sink pin (FLOUTA or FLOUTB) is not used,
Applications Information
the unused current sink must be directly connected
to OUT, which disables that channel.
LED Selection
The movie-mode output current is controlled by the
The AAT1270 is specifically designed to drive white
flash LEDs (typical forward voltage of 2.5V to
4.5V). Since the FLOUTA and FLOUTB input cur-
rent sinks are matched with low voltage depend-
ence; the LED-to-LED brightness will be matched
regardless of the individual LED forward voltage
(VF) levels.
2
EN/SET pin, which uses a single-wire S Cwire
interface to adjust the output current to one of 16
different levels. As shown in Table 1, the current
settings are in logarithmic scale where each code
is 1dB below the previous code. The FLEN signal
takes priority over movie-mode operation.
In mobile GSM systems where the phone remains in
constant contact with the base station by regular
communication, a FLINH pin is provided to prevent
the camera flash and PA transmission pulses from
occurring simultaneously, potentially causing the bat-
tery voltage to drop below the system’s undervoltage
lockout threshold (UVLO) or creating unwanted EMI.
Flash Mode LED Current
The LED current is controlled by the RSET resistor.
For maximum accuracy, a 1% tolerance resistor is
recommended. FLOUTA and FLOUTB can be pro-
grammed up to a maximum total flash current of
1A, or up to 500mA per channel. FLOUTA and
FLOUTB output current is matched across the pro-
gramming range.
During a flash event, strobing the FLINH pin low-to-
high will reduce the LED current to the maximum
movie mode current level for the duration of FLINH.
Strobing FLINH high-to-low will instruct the AAT1270
to revert the flash LED current to its default (maxi-
mum) level assuming that the FLEN pin is still active
(HIGH) and that the flash timer has not expired.
The maximum flash current in each FLOUTA and
FLOUTB is set by the RSET resistor and can be cal-
culated using the following equation:
81kΩ ⋅ A 81kΩ ⋅ A
= 500mA per channel
IFLOUTA = IFLOUTB
=
=
RSET
162kΩ
Over-Temperature Protection
Movie Mode LED Current
In the default movie mode, the corresponding
FLOUTA/FLOUTB movie mode current can be cal-
culated:
Thermal protection disables the AAT1270 when
internal power dissipation becomes excessive, as it
disables both MOSFETs. The junction over-tem-
perature threshold is 140°C with 15°C of tempera-
ture hysteresis. The output voltage automatically
recovers when the over-temperature fault condition
is removed.
IFLOUT[A/B]MAX
7.3
IMOVIE MODE[A/B]
=
For example, if an RSET value of 162kΩ is chosen,
then the FLOUTA/FLOUTB flash current is set to
500mA. For movie mode operation, the maximum
current available at either FLOUTA or FLOUTB is
then:
Over-Voltage Protection
(Open LED, Open Circuit)
The AAT1270’s output voltage is limited by internal
over-voltage protection circuitry, which prevents
damage to the AAT1270 from open LED or open
circuit conditions.
IFLOUT[A/B]MAX 500mA
=
IMOVIE MODE[A/B]
=
= 68.5mA
7.3
7.3
During an open circuit, the output voltage rises and
reaches 5.5V (typical), and the OVP circuit dis-
ables the switching, preventing the output voltage
from rising higher. Once the open circuit condition
is removed, switching will resume. The controller
will return to normal operation and maintain an
average output voltage.
2
Alternatively, the AAT1270 S Cwire interface pro-
grams the movie mode current at a reduced level.
The FLOUTA/FLOUTB movie-mode current can be
adjusted in logarithmic fashion to one of 16 steps.
Table 1 illustrates approximate movie mode levels
10
1270.2007.07.1.0
5秒后页面跳转
资料手册解读：UC3842参数和管脚说明
一文带你了解无源晶振的负载电容为何要加两颗谐振电容CL1和CL2
玻璃管保险丝与陶瓷管保险丝：区别与替代性探讨
PCF8574资料解读：主要参数分析、引脚说明
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
数据手册
如果您发现信息不准确，
