ADP8860 Analog Devices, ADP8860 Datasheet - Page 20

• Manufacturer Part Number: ADP8860
• Description: Charge Pump, 7-Channel Smart LED Driver with I2C Interface
• Manufacturer: Analog Devices

Specifications of ADP8860

• Vin Range: 2.4V to 5.5V
• Vout (v): 4.3 to 5.5
• Synchronous: No
• Package: 20-Lead WLCSP
• Led Configuration: Parallel
• Topology: Capacitive
• I2c Support: Yes
• Max Iout (ma): 60mA
• Brightness Control: I2C
• Peak Efficiency (%): 89%
• Switching Frequency: 1MHz

ADP8860
contains programmable hysteresis, meaning that the photo-
sensor output must rise above L3_TRP + L3_HYS before
L3_OUT clears. L3_CMPR is enabled via the L3_EN bit. The
L3_TRP and L3_HYS values of L3_CMPR can be set between
0 μA and 137.7 μA (typical) in steps of 0.54 μA (typical).
Note that the full-scale value of the L2_TRP and L2_HYS
registers is 250 (decimal). Therefore, if the value of L2_TRP +
L2_HYS exceeds 250, the comparator output is unable to
deassert. For example, if L2_TRP is set at 204 (80% of the full-
scale value, or approximately 0.80 × 1080 μA = 864 μA), then
L2_HYS must be set at less than 46 (250 − 204 = 46). If it is not,
then the L2_HYS + L2_TRP exceeds 250 and the L2_CMPR
comparator is never allowed to go low.
When both phototransistors are enabled and programmed
in automatic mode (through Bit L3_EN and Bit L2_EN in
Register 0x1B and Register 0x1C), the user application needs
to determine which of the comparator outputs to use, selecting
Bit SEL_AB in Register 0x04 for automatic light sensing
transitions. For example, the user’s software may select the
comparator of the phototransistor exposed to higher light
intensity to control the transition between the programmed
backlight intensity levels.
The L2_CMPR and L3_CMPR comparators can be enabled
independently of each other, or can operate simultaneously. A
single conversion from each ADC takes 80 ms (typical). When
CMP_AUTOEN is set for automatic backlight adjustment (see
the Automatic Backlight Adjustment section), the ADC and
comparators run continuously. If the backlight is disabled and
at least one independent sink is enabled, it is possible to use the
light sensor comparators in a single shot mode. A single shot
read of the photocomparators is performed by setting the
FORCE_RD bit. After the single shot measurement is completed,
the internal state machine clears the FORCE_RD bit.
The interrupt flags (CMP_INT and CMP_INT2) can be used to
notify the system when either L2 or L3 changes state. Refer to
the Interrupts section for more information.
1
Figure 40. Comparator Ranges
L3_TRP
L3_HYS
ADC RANGE (µA)
L2_TRP
L2_HYS
10
100
1000
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AUTOMATIC BACKLIGHT ADJUSTMENT
The ambient light sensor comparators can automatically
transition the backlight between one of its three operating
levels. To enable this mode, set the CMP_AUTOEN bit in
Register 0x01.
When enabled, the internal state machine takes control of the
BLV bits and changes them based on the L2_OUT and L3_OUT
status bits. When L2_OUT is set high, it indicates that the
ambient light conditions have dropped below the L2_TRP point
and the backlight should move to its office (L2) level. When
L3_OUT is set high, it indicates that ambient light conditions
have dropped below the L3_TRP point and the backlight should
move to its dark (L3) level. Table 6 shows the relationship
between backlight operation and the ambient light sensor
comparator outputs.
The L3_OUT status bit has greater priority; therefore, the
backlight operates at L3 (dark) even if L2_OUT is set.
Filter times of between 80 ms and 10 sec can be programmed
for the comparators (Register 0x1B and Register 0x1C) before
they change state.
Table 6. Comparator Output Truth Table
CMP_AUTOEN
0
1
1
1
1
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 (SC1OFF, SC2OFF, SC3OFF, SC4OFF,
SC5OFF, SC6OFF, and SC7OFF) allow the LED current sinks to
be configured in various blinking modes. The on timer can be
set to four different settings: 0.2 sec, 0.6 sec, 0.8 sec, and 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.
X is the don’t care bit.
L3_OUT
X
0
0
1
1
L2_OUT
X
0
1
X
1
1
Backlight Operation
BLV can be manually set
by the user
BLV = 00, backlight
operates at L1 (daylight)
BLV = 01, backlight
operates at L2 (office)
BLV = 10, backlight
operates at L3 (dark)