10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
20
40
60
80
100
120
140
I
O
U
T
(
m
A
)
R
ISET
(k
)
C012
I
LED
=
2000
î
V
BG
R
ISET
LED Current Sinks
8
LED Current Sinks
8.1
Output Configuration
The LP8861-Q1 detects LED output configuration during start-up. Any output connected to ground is
disabled and excluded from adaptive boost control and fault detections. Non-used LED outputs must be
grounded with jumpers J11 through J14.
8.2
Current Setting
Maximum current for the LED outputs is controlled with an external resistor (R4) connected to the ISET
pin. Maximum current can be calculated as follows:
where
•
V
BG
= 1.2 V
•
R
ISET
: current setting resistor (R4), k
Ω
•
I
LED
: output current per output, mA
(3)
Figure 8. Output Current vs R
ISET
8.3
Brightness Control
The LP8861-Q1 controls the brightness of the display with conventional PWM. Output PWM will directly
follow the input PWM. Input PWM frequency can be in the range of 100 Hz to 20 kHz.
An external digital PWM signal can be connected to connector J18. For test purposes the PWM input of
the LP8861-Q1 can be connected to ground to turn off LEDs or connected to VDDIO/EN to set up 100%
brightness using jumper J2.
12
LP8861-Q1EVM Evaluation Module
SNVU456 – July 2015
Copyright © 2015, Texas Instruments Incorporated