ADP5501 Analog Devices, ADP5501 Datasheet - Page 14

• Manufacturer Part Number: ADP5501
• Description: Programmable Current Backlight Driver with Ambient Light Sensor Input
• Manufacturer: Analog Devices

Specifications of ADP5501

• Vin Range: 2.7 to 5.5V
• Vout (v): 24 to 27
• Synchronous: No
• Package: 24-Lead LFCSP
• Led Configuration: Serial
• Topology: Inductive
• I2c Support: Yes
• Max Iout (ma): 30mA
• Brightness Control: I2C
• Switching Frequency: 1MHz
• Over Volt Protection (v): 24V

ADP5501
Figure 30 shows a comparison of fading techniques. Cubic fades
complete faster than linear or square fades for a given fade time
setting. Cubic 1 completes approximately 30% faster, and Cubic 2
completes approximately 10% faster, than an equivalent linear
or square fade time.
With four fade laws and 15 fade time settings, the user can
easily find the right fade experience for an application.
AMBIENT LIGHT SENSING
The ADP5501 can be used in conjunction with an external
photosensor to detect when ambient light conditions drop
below programmable set points. An ADC samples the output of
the external photosensor. The ADC result is fed into two pro-
grammable trip comparators. The ADC has an input range of
0 μA to 1000 μA (typical).
The Level 2 (office) light sensor comparator, L2_CMPR, is used
to detect when the photosensor output drops below the pro-
grammable L2_TRIP point. If this event occurs, the L2_OUT
status signal is set. L2_CMPR contains programmable hysteresis,
meaning that the photosensor output must rise above L2_TRIP
+ L2_HYS before L2_OUT is cleared. L2_CMPR is enabled in
Register 0x0C via the L2_EN bit. The L2_TRIP and L2_HYS
values of L2_CMPR can be set between 0 μA and 1000 μA in steps
of 4 μA (typical).
SENSOR
OUTPUT
PHOTO
30
25
20
15
10
5
0
0
Figure 31. Ambient Light Sensing and Trip Comparators
Figure 30. Fade Law Comparison over a Unit Fade Time
ADC
0.2
LINEAR
UNIT FADE TIME
L2_TRIP
L3_TRIP
0.4
SETTINGS
CUBIC 1
FILTER
0.6
L2_HYS
L3_HYS
CUBIC 2
L2_EN
L3_EN
0.8
SQUARE
L2_OUT
L3_OUT
1.0
Rev. 0 | Page 14 of 28
L3_CMPR is used to detect when the photosensor output drops
below the programmable L3_TRIP point. If this event occurs,
the L3_OUT status signal is set. L3_CMPR contains program-
mable hysteresis, meaning that the photosensor output must
rise above L3_TRIP + L3_HYS before L3_OUT is cleared.
L3_CMPR is enabled in Register 0x0C via the L3_EN bit. The
L3_TRIP and L3_HYS values of L3_CMPR can be set between
0 μA and 127 μA in steps of 0.5 μA (typical).
The L2_CMPR and L3_CMPR comparators can be enabled
independently of each other. The ADC and comparators run
continuously when L2_EN and/or L3_EN is set during auto-
matic backlight adjustment mode. A single conversion takes
80 ms (typical). Filter times of between 80 ms and 10 sec can be
programmed for the comparators before they change state.
It is also possible to use the light sensor comparators in a single-
shot mode. After the single-shot measurement is completed, the
internal state machine clears the FORCE_RD bit in Register 0x0C.
The interrupt flag CMPR_INT is set in Register 0x00 if either of
the L2_OUT or L3_OUT status bits changes state, meaning that
interrupts can be generated if ambient light conditions transition
between any of the programmed trip points. CMPR_INT can
cause the INT pin to be asserted if the CMPR_IEN bit is set in
Register 0x01. The CMPR_INT flag can be cleared only by
writing a 1 to it.
AUTOMATIC BACKLIGHT ADJUSTMENT
The ambient light sensor comparators can be used to automat-
ically transition the backlight among its three operating levels. To
enable this mode, the BL_AUTO_ADJ bit is set in Register 0x02.
Once enabled, the internal state machine takes control of the
BL_LVL bits in Register 0x02 and changes them based on the
L2_OUT and L3_OUT status bits in Register 0x0C. The L2_OUT
status bit indicates that ambient light conditions have dropped
below the L2_TRIP point and the backlight should be moved to
its office (L2) level. The L3_OUT status bit indicates that ambient
light conditions have dropped below the L3_TRIP point and the
backlight should be moved to its dark (L3) level. Table 5 shows
the relationship between backlight operation and the ambient
light sensor comparator outputs.
1
Figure 32. Comparator Ranges
ADC RANGE (µA)
L3_TRIP
L3_HYS
L2_TRIP
L2_HYS
10
100
1000