Datasheet

ADP5588 Data Sheet
Rev. C | Page 12 of 28
Light Sensor Inputs
Each light sensor input has two built-in comparators (the L2
comparator and the L3 comparator) with two programmable
trip points, L2 and L3. The trip points are used to select among
three operation modes based on ambient lighting conditions:
outdoor, office, and dark modes.
BRIGHTNESS
L3 L2
DARK OFFICE OUTDOOR
0 LUX
1 kLUX
0µA
1000µA
L2 = 1
L3 = 1
L2 = 1
L3 = 0
L2 = 0
L3 = 0
07673-016
Figure 11. Light Sensor Comparator Modes and Trip Points
L2 Comparator
The L2 comparator is used to detect when the photosensor
output drops below the programmable L2_TRIP point. When
this event occurs, the L2_OUT status signal is set. L2_CMPR
contains programmable hysteresis, meaning that the photo-
sensor output must rise above L2_TRIP + L2_HYS before
L2_OUT is cleared.
L2_CMPR is enabled via the L2_EN bit (Bit 0, Register 0x31 for
Sensor 1 and Bit 0, Register 0x32 for Sensor 2). The L2_TRIP
and L2_HYS values of L2_CMPR can be set between 0 μA and
1000 μA in steps of 4 μA.
L3 Comparator
The L3 comparator is used to detect when the photosensor
output drops below the programmable L3_TRIP point. When
this event occurs, the L3_OUT status signal is set. L3_CMPR
contains programmable hysteresis, meaning that the photo-
sensor output must rise above L3_TRIP + L3_HYS before
L3_OUT is cleared. L3_CMPR is enabled via the L3_EN bit.
The L3_TRIP and L3_HYS values of L3_CMPR can be set
between 0 μA and 127.5 μA in steps of 0.5 μA.
L3_TRIP
L2_TRIP
L3_HYST
L2_HYST
1 10 100 1000
ADC RANGE (µA)
07673-017
Figure 12. Comparator Ranges
The L2_CMPR and L3_CMPR comparators can be enabled
independently of each other, and the ADC and comparator(s)
run continuously when L2_EN and/or L3_EN is set.
Photosensor Operation
The comparator inputs remain idle until enabled, at which
point they detect lighting conditions from the photosensor
output. Depending on lighting conditions, and where the L2
and L3 trip points are set in the comparator level trip registers
(Register 0x33 through Register 0x3A), the comparators set a
value of 1 or 0 to L2_OUT and L3_OUT. The values of L2 and
L3 determine what mode or setting adjustment is required for a
particular lighting condition. Figure 11, Figure 12, and Table 15
summarize the mode settings and logical values of L2 and L3.
Table 15. L2_OUT and L3_OUT Comparator Mode
Combination
L3 L2 Mode
0 0 Outdoor
0 1 Office
1 1 Dark
It is also possible to use the light sensor comparators in single-
shot mode. A single-shot measurement is done when the
FORCE_RD bit in Register 0x31 is set. After the single-shot
measurement is completed, the internal state machine clears the
FORCE_RD bit. It takes 80 ms for a complete conversion. To
reduce the potential for flickering, the sensors can be programmed
for a number of sequential readings. The filter settings in
Register 0x31 and Register 0x32 determine the number of
sequential readings needed by the user; these settings range
from 80 ms to 10.24 sec.
L2_TRIPL2_HYST
FILTER
SETTING
L2_EN
L2_OUT
L3_OUT
COMP
INPUT
ADC
PHOTO-
SENSOR
L3_EN
V
CC
L2_CMP
L3_CMP
L3_TRIPL3_HYST
07673-018
Figure 13. Light Sensor and Trip Points Block Diagram