APW7008(2009_06) Ver la hoja de datos (PDF) - Anpec Electronics
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APW7008 Datasheet PDF : 22 Pages
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APW7008
Function Description
Soft-Start
The APW7008 provides the soft-start function to limit the
inrush current during start-up. 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 APW7008 operates in 1x, 1.5x, and 2x charge pump
modes and automatically switches the charge pump
modes depend on the input voltage to maintain the re-
quired power for high power efficiency. If the APW7008
operates in 1x mode, the VOUT is pulled up to the VIN.
When the VIN decreases, the VILED will decease to main-
tain the regulated LED current. Until the 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 the VIN continues to decrease until the VILED
is below 100mV again, the device will switch to 2x mode.
When the VIN rises and reaches by approximately VOUT-
300mV, the APW7008 switches back to 1.5x mode. If
the VIN continues to rise and reach by approximately
VOUT+300mV, the APW7008 switches back to 1x mode.
The 2x charge pump is enough to suffice the White LED
for a Li-ion battery application. The APW7008 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 APW 7008 provides three logic input pins to en-
able 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 respective LED channels.
Table 1. The Truth Table of Control Logic Pins
Control Logic Pin
CTRL2 CTRL1 CTRL0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
LED4
OFF
OFF
OFF
ON
OFF
OFF
ON
OFF
LED Status
LED3 LED2
OFF OFF
OFF ON
ON OFF
OFF OFF
OFF ON
ON ON
ON ON
OFF OFF
LED1
ON
OFF
OFF
OFF
ON
ON
ON
OFF
LED Current Setting
Connect a resistor from ISET pin to GND to set the LED
current. The ISET voltage is typically 1.2V, the LED cur-
rent is typically 400 times the current through the ISET
resistor. The LED current is given by:
RSET
=
400 × 1.2V
ILED
The APW7008 provides up 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%
precision surface mount resistor for the need.
Table 2. RSET Value Selection
ILED (mA)
5
10
15
20
30
RSET (kΩ)
92
47
32
24
16.5
Copyright © ANPEC Electronics Corp.
13
Rev. A.4 - Jun., 2009
www.anpec.com.tw
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