LP39542 Datasheet, PDF (12/58 Pages) National Semiconductor (TI) – Advanced Lighting Management Unit

Functionality of Color LED Outputs (R1, G1, B1; R2, G2, B2)
LP39542 has 2 sets of RGB/color LED outputs. Both sets
have 3 outputs and the sets can be controlled in 4 different
ways:
1. Command based pattern generator control (internal
PWM)
2. Audio synchronization control
3. Programmable ON/OFF blinking sequences for RGB1
4. External PWM control
By using command based pattern generator user can pro-
gram any kind of color effect patterns. LED intensity, blinking
cycles and slopes are independently controlled with 8 16-bit
commands. Also real time commands are possible as well as
loops and step by step control. If analog audio is available on
system, the user can use audio synchronization for syn-
chronizing LED blinking to the music. The different modes
together with the various sub modes generate very colorful
and interesting lighting effects. Direct ON/OFF control is
mainly for switching on and off LEDs. External PWM con-
trol is for applications where external PWM signal is available
and required to control the color LEDs. PWM signal can be
connected to any color LED separately as shown later.
COLOR LED CONTROL MODE SELECTION
The RGB_SEL[1:0] bits in the Enables register (08H) control
the output modes for RGB1 (R1, G1, B1) and RGB2 (R2, G2,
B2) outputs as seen in the following table.
RGB_SEL Audio sync
[1:0]
Pattern
generator
Blinking
control
00
-
RGB1 & RGB2
-
01
-
RGB2
RGB1
10
RGB2
RGB1
-
11
RGB1 & RGB2
-
-
RGB Control register (00H) has control bits for direct on/off
control of all color LEDs. Note that the LEDs have to be turned
on in order to control them with audio synchronization or pat-
tern generator.
The external PWM signal can control any LED depending on
the control register setup. External PWM signal is connected
to PWM/SYNC pin. The controls are in the Ext. PWM Control
register (address 07H) except the FLASH control in HC_Flash
(10H) register as follows:
Ext. PWM Control (07H)
wled1-4_pwm bit 7 PWM controls WLED 1-4
wled5-6_pwm bit 6 PWM controls WLED 5-6
r1_pwm
bit 5 PWM controls R1 output
g1_pwm
bit 4 PWM controls G1 output
CURRENT CONTROL OF COLOR LED OUTPUTS (R1, R2,
G1, G2, B1, B2)
Both RGB output sets can be separately controlled as con-
stant current sinks or as switches. This is done using
cc_rgb1/2 bits in the RGB control register. In constant current
mode one or both RGB output sets are controlled with con-
stant current sinks (no external ballast resistors required).
The maximum output current for both drivers is set by one
external resistor R_RGB. User can decrease the maximum cur-
rent for an individual LED driver by programming as shown
later.
The maximum current for all RGB drivers is set with R_RGB.
The equation for calculating the maximum current is
I_MAX = 100 × 1.23V / (R_RGB + 50Ω)
where
I_MAX - maximum RGB current in any RGB output in constant
current mode
1.23V - reference voltage
100 - internal current mirror multiplier
R_RGB- resistor value in Ohms
50Ω - internal resistor in the I_RGB input
For example if 22mA is required for maximum RGB current
R_RGB equals to
R_RGB=100×1.23V / I_MAX–50Ω=123V / 0.022A–50Ω=5.54kΩ
Each individual RGB output has a separate maximum current
programming. The control bits are in registers RGB1 max
current and RGB2 max current (12H and 13H) and pro-
gramming is shown in table below. The default value after
reset is 00b.
IR1[1:0], IG1[1:0],
IB1[1:0], IR2[1:0],
IG2[1:0], IB2[1:0]
00
01
10
11
Maximum
current/output
0.25 × I_MAX
0.50 × I_MAX
0.75 × I_MAX
1.00 × I_MAX
SWITCH MODE
The switch mode is used if there is a need to connect parallel
LEDs to output or if the RGB output current needs to be in-
creased.
Please note that the switch mode requires an external bal-
last resistors at each output to limit the LED current.
The switch/current mode and on/off controls for RGB are in
the RGB_ctrl register (00H).
b1_pwm
bit 3 PWM controls B1 output
r2_pwm
bit 2 PWM controls R2 output
g2_pwm
bit 1 PWM controls G2 output
b2_pwm
bit 0 PWM controls B2 output
HC_Flash (10H)
hc_pwm
bit 5 PWM controls FLASH
Note: If DISPL=1, wled1-4pwm controls WLED1-6
Note: Maximum external PWM frequency is 1kHz. If during the external
PWM control the internal PWM is on, the result will be product of both
functions.
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