AAT1407 Advanced Analogic Technologies, Inc., AAT1407 Datasheet - Page 10

• Manufacturer Part Number: AAT1407
• Description: 6 Channel Led Backlight Driver With Integrated Boost And High Frequency Direct Pwm Dimming
• Manufacturer: Advanced Analogic Technologies, Inc.

adjustable up to 1300kHz for optimum efficiency and the
smallest external filtering components. Alternatively, the
device may be synchronized to an external clock. Current
mode control provides fast response to line and load
transients. Integrated light load mode ensures highest
efficiency across the entire input voltage and load range.
Fault tolerant circuitry extends system life by disabling
open LED strings. The high voltage current sinks main-
tain normal operation with non-matched strings while
also preventing damage due to shorted LEDs.
The AAT1407 is available in a Pb-free, thermally enhanced
24-pin 3x4mm TQFN package.
PWM Dimming
The AAT1407 provides direct PWM dimming. After initial
power-up or when EN is cycled, the device is enabled
with brightness controlled by the PWM duty cycle and
the R
The ultra-fast 1μs turn-on and turn-off time of the boost
regulator and current sinks ensures high performance
and excellent dimming range in applications requiring
high frequency PWM dimming. The high PWM dimming
frequency eliminates audio interference. The integrated
current sinks ensure good timing between strings (PWM
matching) while the fast response yields a linear PWM
duty-cycle versus LED current characteristic. PWM inputs
from 100Hz to 100kHz are recommended.
10
SwitchReg
SET
100000
10000
1000
100
resistor value.
10
1
Figure 1: PWM Input Frequency
1
TM
6 Channel LED Backlight Driver with Integrated Boost and High Frequency Direct PWM Dimming
AAT1407 Dimming Range
vs. PWM Pin Frequency
vs. Dimming Range.
10
PWM Frequency (Hz)
100
1000
10000
w w w . a n a l o g i c t e c h . c o m
100000
Fault Tolerant Operation
The AAT1407 device is protected from faults arising from
LED opens and/or shorts.
An LED open condition will be detected by the controller
at startup and during normal operation. The low voltage
on the current sink is detected by the controller, which
disables the feedback to the boost converter from that
current sink. The remaining LED strings continue to
operate normally. The controller re-enables the disabled
current sink feedback if the LED open condition is
removed during a power or EN cycle. This feature
extends backlight life and reliability, which is otherwise
limited by intermittent conditions in the LED string(s)
and/or circuit board interconnections.
Under all conditions, the over-voltage protection circuitry
prevents the switching node (LX) from exceeding the
maximum operating voltage prior to disabling the current
sink. Over-voltage protection (OVP) disables boost switch-
ing while maintaining the programmed LED current. Boost
switching is re-enabled when OVP hysteresis is satisfied.
A LED short condition results in a higher voltage appear-
ing on the affected channels' current-sink pin. The
affected current sink automatically compensates for the
additional voltage. The current sink can withstand a high
voltage indefinitely. However, the increased voltage
across the current sink causes an increase in power dis-
sipation. The channel will continue to operate until the
over-temperature protection activates.
Integrated over-current protection is provided. Over-
current protection prevents inductor saturation and any
resulting damage to the switching device occurring dur-
ing an overload fault condition.
PRODUCT DATASHEET
AAT1407
1407.2010.06.1.0