ADP8866 Analog Devices, ADP8866 Datasheet - Page 15

• Manufacturer Part Number: ADP8866
• Description: Charge Pump Driven 9-Channel LED Driver with Automated LED Lighting Effects
• Manufacturer: Analog Devices

Specifications of ADP8866

• Vin Range: 2.5 to 5.5V
• Vout (v): 4.3 to 5.5
• Synchronous: No
• Package: 20-Lead LFCSP
• Led Configuration: Parallel
• Topology: Capacitive
• I2c Support: Yes
• Max Iout (ma): 25mA
• Brightness Control: I2C
• Peak Efficiency (%): 92%
• Switching Frequency: 1MHz

The fade profile is based on the transfer law selected (square,
Cubic 10, or Cubic 11) and the delta between the actual current
and the target current. Smaller changes in current reduce the
fade time. For square law fades, the fade time is given by
where the Fade Rate is shown in Table 6.
Table 6. Available Fade-In and Fade-Out Times
Code
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
The Cubic 10 and Cubic 11 laws also use the square backlight
currents in Equation 3; however, the time between each step is
varied to produce a steeper slope at higher currents and a
shallower slope at lighter currents (see Figure 32).
CABC FADE DISABLE
The fade settings applied to the backlight in Register 0x12 are
also used when the BLMX (Register 0x13) current is changed.
This provides a smooth transition to new backlight current
levels.
However, in some modes of operation, this feature is not
desired. For example, during cABC (content adjustable
Figure 32. Comparison of the Dimming Transfers Law 25 mA Scale Shown
Fade Time = Fade Rate × (Code/127)
30
25
20
15
10
5
0
0
Fade Rate (Seconds per 128 Codes)
0.0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.75
1.0
1.25
1.50
1.75
0.25
UNIT FADE TIME
SQUARE
0.50
CUBIC 10
0.75
CUBIC 11
1.00
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(4)
brightness control) operation, the BLMX register is updated as
often as 60 times per second. And the changes to BLMX must
be implemented as soon as possible. Therefore, the ADP8866
has a unique mode that allows the backlight to have very fast
changes after the initial ramp in and ramp out. This mode is
entered when CABCFADE in Register 0x10 is set high.
In this mode, the backlight fades in when BL_EN and nSTBY in
Register 0x01 are set high, and it fades out when BL_EN or
nSTBY is set low. However, after the fade-in is complete, any
changes to the BLMX register result in near instantaneous
changes to the backlight current. The situation is illustrated in
Figure 33.
INDEPENDENT SINK CONTROL (ISC)
Each of the nine LEDs can be configured (in Register 0x10 and
Register 0x11) to operate as either part of the backlight or an
independent sink current (ISC). Each ISC can be enabled
independently and has its own current level. All ISCs share the
same fade-in rates, fade-out rates, and fade law.
The ISCs have additional timers to facilitate blinking functions.
A shared on timer (SCON), used in conjunction with the off
timers of each ISC (SC1OFF, SC2OFF, SC3OFF, SC4OFF,
SC5OFF, SC6OFF, and SC7OFF; see Register 0x1C through
Register 0x21) allow the LED current sinks to be configured in
various blinking modes. The on and off times are listed in the
Register Descriptions section. Blink mode is activated by setting
the off timers to any setting other than disabled.
MAX
BL EN = 1
CURRENT
SCx
SCx_EN
SET BY USER
FADE-IN
ON TIME
Figure 34. LEDx Blink Mode with Fading
Figure 33. Effect of the CABCFADE Bit
FADE-OUT FADE-IN
CABCFADE = 0 (DEFAULT)
CABCFADE = 1
TIME
OFF
TIME
ON TIME
BL EN = 0
FADE-OUT
ADP8866
TIME
OFF