AP3156 Datasheet, PDF (9/15 Pages) Diodes Incorporated – HIGH EFFICIENCY 1X/1.5X/2X CHARGE PUMP FOR WHITE LED APPLICATIONS

AP3156
HIGH EFFICIENCY 1X/1.5X/2X CHARGE PUMP
FOR WHITE LED APPLICATIONS
Functional Description
The AP3156 is a tri-mode high efficiency six-channel charge
pump (1x, 1.5x or 2x) device intended for white LED backlight
applications. An internal comparator circuit compares the
voltage at each constant current sink input against a reference
voltage. To ensure maximum power efficiency, the most
appropriate switching mode (1x, 1.5x, 2x) is automatically
selected.
The AP3156 requires only four external components: two 1µF
ceramic flying capacitors (C1 and C2) for the charge pump, one
1µF ceramic input capacitor (CIN), and one 1µF ceramic
charge pump output capacitor (COUT).
The each output channel of the AP3156 can drive six
individual LEDs with a maximum current of 25mA per channel.
These can be paralleled to give a total output current of
150mA.
Constant Current Output Level Settings
The constant current level for the outputs is set via the Serial
Digital Interface and has a logarithmic variance. This results in
the LED brightness varying linearly when the settings in the
scale are traversed. Because the inputs D1 to D6 are true
independent constant current sinks, the voltage observed on
any single given input will be determined by the difference
between VOUT and the actual forward voltage (VF) of the LED
being driven.
Since the constant current levels for the AP3156 are
programmable, no PWM (pulse width modulation) or additional
control circuitry is needed to control LED brightness. With its
high-speed serial interface (>1MHz data rate), the LED current
drive of the AP3156 can be changed successively to brighten
or dim LEDs in smooth transitions or in abrupt steps, giving the
user complete programmability and real-time control of LED
brightness.
There are 32 current level settings separated from one another
by approximately 0.5dB (see Constant Current Programming
Level table). Code 1 is full-scale current, and Code 31 is full
scale attenuated roughly 15dB. Code 32 is reserved as a “no
current” setting.
Constant Current Programming Levels (mA)
Data
20mA Max
IOUT (mA)
25mA Max
IOUT (mA)
1
20
25
2
18.9
23.6
3
17.8
22.3
4
16.8
21.0
5
15.9
19.9
6
15.0
18.7
7
14.2
17.7
8
13.4
16.7
9
12.6
15.8
10
11.9
14.9
11
11.2
14.1
12
10.6
13.3
13
10.0
12.5
14
9.5
11.8
15
8.9
11.2
16
8.4
10.5
17
8.0
10.0
18
7.5
9.4
19
7.1
8.9
20
6.7
8.4
21
6.3
7.9
22
6.0
7.5
23
5.6
7.0
24
5.3
6.7
25
5.0
6.3
26
4.7
5.9
27
4.5
5.6
28
4.2
5.3
29
4.0
5.0
30
3.8
4.7
31
3.6
4.4
32
0
0
Low Current Output Level Setting
The AP3156 has a distinct Low Current mode with ultra-low
quiescent current. For drive currents of 2mA or less, the device
operates with significantly reduced quiescent current.
Low Current Programming Levels (mA)
Data
Current (mA)
1
2
2
1
3
0.5
4
0.05
5
0
Serial Digital Interface
SDI is a general purpose 1-wire digital interface designed to
transport digital controls for power management ICs such as
AP3156. The current levels of the six channels can be
configured either together, individually or specific grouping.
Up to 32 current levels are allowed. A generic system
controller can easily support the SDI protocol via bit-banging
over its general purpose I/Os.
The SDI protocol is simple yet flexible enough to
accommodate different switching clock frequencies. Any
sequence of negative-edged pulses of 63 or less (see
Instruction & Data Table) separated by TSEP at the SDI pin is
interpreted by the AP3156 as a channel configuration event.
In future, the number of pulses can be extended to support
additional commands.
AP3156 Rev. 1
9 of 15
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SEPTEMBER 2009
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