The AP3031 is an inductor-based DC/DC boost converter designed to drive LED arrays. 1.4A switching
current allows AP3031 to be used in different 7' to 10'
LCD panel backlights (3*13 LED arrays typically).
A constant frequency 1MHz PWM control scheme is
employed in this IC, which means tiny external components can be used. Specifically, 1mm tall 4.7
inductor and 0.47
application is sufficient.
The over output voltage protection is equipped in
AP3031, which protects the IC under open load condition. The AP3031 includes UVLO, soft-start, current
limit and OTSD to protect the circuit.
The AP3031 is available in standard SOT-23-6, TSOT23-6 and SOIC-8 packages.
14SWSwitch Pin. Connect external inductor and Schottky
22, 3, 6GND Ground Pin
31FB Voltage Feedback Pin. Reference voltage is 200mV
4
57OVOver-voltage Protection Input Pin. Connect to the output directly. On OVP condition, the out-
65 V
Pin NameFunction
Enable and Dimming Control Pin. Connect to a high input to enable the IC or a low input to
disable the IC.
8CTRL
If logic low time ismore than about 0.7ms and then enable the IC, the AP3031 will soft start to
protect system departments. If logic low time is less than about 0.7ms and then enable the IC,
the AP3031 will hold on standby mode and start directly to achieve high frequency dimming
Thermal Resistance
(Junction to Ambient, No Heat Sink) θ
Operating Junction TemperatureT
Storage Temperature RangeT
Lead Temperature (Soldering, 10sec)T
LEAD
IN
SW
FB
CTRL
JA
J
STG
SOT-23-6/TSOT-23-6265
SOIC-8120
20V
38V
20V
20V
150
-65 to 150
260
o
C/W
o
C
o
C
o
C
ESD (Machine Model)600V
ESD (Human Body Model)4000V
Note 1:Stresses greater than those listed under "Absolute Maximum Ratings" may cause permanent damage to the device.
These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated
under "Recommended Operating Conditions" is not implied. Exposure to "Absolute Maximum Ratings" for extended periods
may affect device reliability.
Note 2: The bold type specifications of full temperature range are guaranteed by design (GBD).
Note 3: The switch current limit is related to duty cycle. Please refer to Figure 15 for detail.
The AP3031 is a boost DC-DC converter which uses a
constant frequency, current mode control scheme to
provide excellent line and load regulation. Operation
can be best understood by referring to Figure 3 and
Figure 24.
At the start of each oscillator cycle, switch Q1 turns on.
The switch current will increase linearly. The voltage
on sense resistor is proportional to the switch current.
The output of the current sense amplifier is added to a
stabilizing ramp and the result is fed into the noninversion input of the PWM comparator A2. When this
voltage exceeds the output voltage level of the error
amplifier A1, the switch is turned off.
It is clear that the voltage level at inversion input of A2
sets the peak current level to keep the output in
regulation. This voltage level is the output signal of
error amplifier A1, and is the amplified signal of the
voltage difference between feedback voltage and
reference voltage of 200mV. So, a constant output
current can be provided by this operation mode.
LED Current Control
Refer to Figure 24, the LED current is controlled by the
feedback resistor R
determined by the feedback voltage and resistor R
so the precise resistors are preferred. The resistance of
is in inverse proportion to the LED current since
R
ISET
the feedback reference is fixed at 200mV. The relation
for R
and LED current (I
ISET
below:
. LEDs' current accuracy is
ISET
)can be expressed as
LED
ISET
Soft Start
The AP3031 has an internal soft start circuit to limit
the inrush current during startup. If logic low time on
CTRL pin is more than about 0.7ms and then enable
the IC, the AP3031 will start smoothly to protect the
supplier. The time of startup is controlled by internal
soft-start capacitor. Details please refer toFigure 18.
V
CTRL
5V/div
V
SW
5V/div
I
L
500mA/div
V
OUT
10V/div
Time 80μs/div
Figure 18. Soft-start Waveform
V
=5V, 3×13 LEDs, I
IN
LED
=260mA
Standby and Dimming
To avoid audio noise and achieve high frequency dimming, AP3031 is equipped with standby function. If
logic low time on CTRL pin is less than about 0.7ms
and then enable the IC, the AP3031 will hold on
standby mode and start directly to achieve high frequency dimming. Details please refer to Figure 19.
,
V
CTRL
5V/div
V
SW
5V/div
I
L
500mA/div
V
OUT
10V/div
Time 80μs/div
Over Voltage Protection
The AP3031 has an internal open load protection
circuit. When the LEDs are disconnected from circuit
or fail open, the output voltage is clamped at about
17.5V. The AP3031 will switch at a low frequency, and
minimize current to avoid input voltage drop.
Two typical types of dimming control circuit are
present as below. First, controlling CTRL Pin voltage
to change operation state is a good choice. Second,
10
Page 11
Data Sheet
R1
FB
AP3031
R2R3
V
DC
Effective
Feedback Voltage
R1
FB
AP3031
R2
R3
PWM
R4
C
Effective
Feedback Voltage
AP3031
CTRL
WHITE LED STEP-UP CONVERTER AP3031
Application Information (Continued)
changing the feedback voltage to get appropriate duty
and luminous intensity is also useful.
(1) Adding a Control Signal to CTRL Pin
Adding a PWM signal to CTRL pin directly, the
AP3031 is turned on and off by this signal. When the
PWM frequency is lower than 1kHz(Typ.), the IC
works in the soft-start mode to dimming the light. On
contrary, when the PWM frequency is higher than
1kHz(Typ.), the IC works in the standby mode: the
converter ceaselessly switches off and directly starts to
achieve light dimming. This standby function allows
AP3031 to support high frequency dimming (up to
25kHz or higher) to avoid audio noise. More details
please refer to Figure 20 and Figure 21.
Figure 20. Dimming Control
Using a PWM Signal in CTRL Pin
Comparing with all kinds of PWM signal control, this
method features a stable output voltage and LEDs
current. Please refer to Figure 22.
Using DC Voltage
Figure 22. Dimming Control
Second, using a filtered PWM signal can do it. The
filtered PWM signal can be considered as a varying
and adjustable DC voltage, please refer to Figure 23.
V
CTRL
2.5V/div
V
SW
5V/div
I
L
500mA/div
Using Filtered PWM Voltage
Time 20μs/div
Figure 23. Dimming Control
Figure 21. High Frequency (25kHz)
Dimming Waveform
(2) Changing the Effective Feedback Voltage
There are two popular methods to change the effective
feedback voltage.
First, adding a constant DC voltage through a resistor
divider to FB pin can control the dimming. Changing
the DC voltage or resistor between the FB Pin and the
DC voltage can get appropriate luminous intensity.
BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifications herein. BCD Semiconductor Manufacturing Limited does not assume any responsibility for use of any its products for any
IMPORTANT NOTICE
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particular purpose, nor does BCD Semiconductor Manufacturing Limited assume any liability arising out of the application or use
of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or
BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifi-
BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifi-
other rights nor the rights of others.
cations herein. BCD SemiconductorManufacturing Limited does not assume any responsibility for use of any its products for any
cations herein. BCD SemiconductorManufacturing Limited does not assume any responsibility for use of any its products for any
particular purpose, nordoes BCD Semiconductor Manufacturing Limited assume anyliability arising out ofthe application or use
particular purpose, nordoes BCD Semiconductor Manufacturing Limited assume anyliability arising out ofthe application or use
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of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or
of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or