Datasheet

ADP8861 Data Sheet
Rev. B | Page 16 of 40
The dim timer and off timer can be used together for sequential
maximum-to-dim-to-off functionality. With both the dim and
off timers programmed, and BL_EN asserted, the backlight turns
on to its maximum setting, and when the dim timer expires, the
backlight changes to its dim setting. When the off timer expires,
the backlight turns off.
MAX
DIM
BL_EN = 1 BL_EN = 0DIM_EN = 1
BACKLIGHT
CURRENT
DIM TIMER
RUNNING
OFF TIMER
RUNNING
SET BY USER
SET BY INTERNAL STATE MACHINE
08391-021
Figure 35. Dim and Off Timers Used Together
FADE OVERRIDE
A fade override feature (FOVR in Register CFGR (0x04)) enables
the host to override the preprogrammed fade in or fade out set-
tings. If FOVR is set and the backlight is enabled in the middle
of a fade out process, the backlight instantly (within approximately
100 ms) returns to its prefade brightness level. Alternatively, if
the backlight is fading in, reasserting BL_EN overrides the pro-
grammed fade in time, and the backlight instantly goes to its final
fade value. This is useful for situations where a key is pressed
during a fade sequence. However, if FOVR is cleared and the
backlight is enabled in the middle of a fade process, the back-
light gradually brightens from where it was interrupted (it does
not go down to 0 and then comes back on).
MAX
BACKLIGHT
CURRENT
BL_EN = 1
BL_EN = 0
BL_EN = 1
BL_EN = 0
BL_EN = 1
(REASSERTED)
FADE-IN
OVERRIDDEN
FADE-OUT
OVERRIDDEN
08391-022
Figure 36. Fade Override Function (FOVR Is High)
INDEPENDENT SINK CONTROL
Each of the seven LEDs can be configured (in Register 0x05) to
operate as either part of the backlight or to operate as an indepen-
dent 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 (SC1_OFF, S C2 _OFF, SC3_OFF, and SC4_OFF
in Register 0x12, and SC5_OFF, SC6_OFF, and SC7_OFF in
Register 0x11) allows the LED current sinks to be configured in
various blinking modes. The on timer can be set to one of four
different settings: 0.2 sec, 0.6 sec, 0.8 sec, or 1.2 sec. The off
timers have four different settings: disabled, 0.6 sec, 1.2 sec, and
1.8 sec. Blink mode is activated by setting the off timers to any
setting other than disabled.
Program all fade, on, and off timers before enabling any of the
LED current sinks. If ISCx is on during a blink cycle and
SCx_EN is cleared, the LED turns off (or fades to off if fade out
is enabled). If ISCx is off during a blink cycle and SCx_EN is
cleared, it stays off.
MAX
ISCx_EN
ISCx
FADE-IN FADE-OUT FADE-IN FADE-OUT
ON TIME ON TIME
OFF
TIME
OFF
TIME
SET BY USER
08391-026
Figure 37. Independent Sink Blink Mode with Fading
SHORT-CIRCUIT PROTECTION MODE
The ADP8861 can protect against short circuits on the output
(VOUT). Short-circuit protection (SCP) is activated at the point
when VOUT < 55% of V
IN
. Note that SCP sensing is disabled
during both startup and restart attempts (fault recovery). SCP
sensing is reenabled 4 ms (typical) after activation. During a
short-circuit fault, the device enters a low current consumption
state and an interrupt flag is set. The device can be restarted at
any time after receiving a short-circuit fault by simply rewriting
nSTBY = 1. It then repeats another complete soft start sequence.
Note that the value of the output capacitance (C
OUT
) should be
small enough to allow VOUT to reach approximately 55% (typical)
of V
IN
within the 4 ms (typical) time. If C
OUT
is too large, the
device inadvertently enters short-circuit protection.