ACT5880
Rev 2, 03-Sep-13
OPEN-DRAIN DRIVERS
The ODO1, the ODO2 and the ODO3 are open-drain
drivers, which could operate as simple open-drain
outputs, or as constant current sinkers, set by
individual configuration. Each of them could also
output in PWM pattern for extended output power
adjustment range. One of the driver output, the
ODO1, has high operation voltage range of up to
40V and the other 2 have the ranges of up to 5V,
make them flexible and powerful.
implemented in the driver circuitry additional to the
current-on slew rate limit of 40mA/μs nominal,
which assure no flicker, no fake operation in various
size for high quality image display.
Figure 7:
The PWM Adjustment Curves.
1
0.9
Non‐linear code
Each driver is configured and manipulated through
the access to respective register bit. Refer to THE
REGISTER BIT DESCRIPTION for more details.
0.8
Expotential Curve
0.7
Linear code
0.6
The BUFFER bit sets how a current setting or PWM
duty cycle affects the output. When the BUFFER is
set to 0, the data written into the respective current
or duty register affects the output instantly; When it
is set to 1, the data written into the register does not
affect the output until the bit is set to 0. This
BUFFER bit has power over all the 3 drivers, which
makes the outputs of drivers change
simultaneously, independent to when the data is
set.
0.5
0.4
0.3
0.2
0.1
0
0
50
100
150
200
250
Operation Modes
Combined Modulations
Constant Current Driving
The PWM pattern could modulate the constant
current output on and off, as well as the simple
open drain output on and off. The combined
modulation extends the dynamic range for backlight
brightness adjustment. For multi-strings backlight
application, the current setting could be used for
matching different strings while the PWM is used for
overall brightness control.
The current is set by configuring the weight for LSB
and a 6 bits current code. Combining the weight
and the current code, the adjustment to current for
each driver covers 0 to 100.8mA nominal.
PWM Switching
Each driver could be turned on and off with an
internal generated PWM pattern at nominal 244Hz.
The duty cycle of PWM pattern is either linear
coded or non-linear coded, optioned against
ordering. If linear coded, the duty cycle is the ratio
of the integer volume put into the duty register over
255. See respective tables for non-linear coded
duty cycle setting and the register setting. Figure 7
shows the duty cycle to code plot for both the linear
and non-linear code, with an exponential curve for
reference.
Inductive Load
For inductive load driving, like driving a vibrator
motor, an external dump clamp diode is desired to
avoid voltage overstress by current breaking
voltage surge caused by the serial inductance. As
specified in the characteristics table, the drivers
have a controlled current on slew rate of 40mA/μs
nominal. This slew rate control only applies on the
turning on of the current, not on the turning off.
The non-linear coded duty cycle setting provides a
close to exponential code to brightness
approximation, which gives similar feeling
difference in changing the code linearly, against the
Webber's law.
Irregular Conditions
The driver block has her own overheat monitoring,
with a threshold temperature lower than the over
temperature shutdown threshold. If overheat is
detected in this block, the drivers are turned off
before the system is possibly forced into thermal-
shutdown. Each driver also has a LED open
detection circuit, which monitors the driving level of
the output stage. When it is driven saturated, then
Phase Shift and Delay
In case of driving backlight assembly with long wire
and close to the EMI sensitive LCD display, both
PWM phase shift and sequential on are
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