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APW7000 Datasheet PDF : 18 Pages
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APW7000
Function Description
Soft-Start
The APW7000 provides the soft-start function to limit the
inrush current during startup. When the input voltage is
supplied to the device and exceeds the UVLO voltage,
the output capacitor is charged directly from input with a
limited current source. Approximate 100µs after the out-
put voltage approaches the input voltage, the device starts
to provide the programmed LED current and determines
which of 1x, and 1.5x, or 2x mode is required. When the
programmed LED current can be reached with 1x mode,
the soft-start is completed and the device operates in 1x
mode. When the programmed LED current cannot be
reached, the charge pump goes into 1.5x mode. If the
1.5x mode charge pump cannot suffice for the LED cur-
rent need, the charge pump will switch to 2x mode.
Mode Transition
The APW7000 operates in 1x, 1.5x and 2x charge pump
modes and automatically switches the charge pump
modes depend on the input voltage to main tain the re-
quired power for high power efficiency. If the APW7000
operates in 1x mode, the VOUT is pulled up to VIN. When
VIN decreases, the VILED will decease to maintain the
regulated LED current. Until VILED is below 100mV, the
device will switch to 1.5x mode. In 1.5x mode, the VILED
is regulated to 0.18V, and the output voltage is VF+0.18V.
If VIN continues to decrease until VILED is below 100mV
again, the device will switch to 2x mode. When the VIN
rises and reaches by approximately VOUT-300mV, the
APW7000 switches back to 1.5x mode. If the VIN contin-
ues to rise and reaches by approximately VOUT+300mV,
the APW7000 switches back to 1x mode. The 2x charge
pump is enough to suffice the White LED for a Li-ion
battery application. The APW7000 ensures that in the 1x
mode for as long as possible to increase the efficiency
and extend the operating range by using the 2x mode.
The transition voltages from 1x to 1.5x and 1.5x to 2x are
given by:
VTRANS1X = VF + 0.1V + (IOUT x ROUT1X)
VTRANS1.5X = [VF + 0.1V + (IOUT x ROUT1.5X)] / 1.5
where VF is the forward voltage of LED
IOUT is the output current
ROUT1X is the output impedance in 1x mode = 1.6Ω
ROUT1.5X is the output impedance in 1.5x mode = 7Ω
Control Logic Pins
The APW7000 provides three logic input pins to enable
or disable a combination of LEDs. Table1 shows the truth
table of the logic pins. If the LED channels are not used,
connecting the ILED pins to VOUT to turn off the respec-
tive LED channels.
Control Logic Pin
LED Status
CTRL2 CTRL1 CTRL0 LED4 LED3 LED2 LED1
0
0
0 OFF OFF OFF ON
0
0
1 OFF OFF ON OFF
0
1
0 OFF ON OFF OFF
0
1
1
ON OFF OFF OFF
1
0
0 OFF OFF ON ON
1
0
1 OFF ON ON ON
1
1
0
ON ON ON ON
1
1
1 OFF OFF OFF OFF
Table1. The Truth Table of Control Logic Pins
LED Current Setting
Connect a resistor from ISET pin to GND to set the LED
current. The ISET voltage is typically 1.2V, and the LED
current is typically 400 times the current through the ISET
resistor. The LED current is given by:
RSET = 400 ×1.2V
ILED
The APW7000 provides up to 30mA of LED current per
LED and the device has a max current matching of ±5%
between any two LED currents and a max current accu-
racy of ±8%. If high accuracy is required, using a 1% pre-
cision surface mount resistor for the need.
ILED (mA)
5
10
15
20
30
RSET (kΩ)
92
47
32
24
16.5
Table2. RSET Value Selection
Copyright © ANPEC Electronics Corp.
10
Rev. A.2 - Feb., 2009
www.anpec.com.tw
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