LTC3212 Datasheet, PDF (8/12 Pages) Linear Technology – RGB LED Driver and Charge Pump

LTC3212
Operation
White Mode
The LTC3212 has a white mode that automatically scales
the current in the red, green and blue LEDs to a preset mix
when selected. This allows the currents programmed with
the external resistors to be set independently of the ratio
needed for white light, increasing the flexibility of program-
ming other colors. The intensity of the white is set by the
resistor on I_SETG. The ratio used for white mode is:
I_LEDG
=
177.6
R_SETG
I_LEDR
=
159.8
R_SETG
I_LEDB
=
133.2
R_SETG
Enable
Each LED driver output may be programmed on or off
by pulsing the LEDEN pin while enabling the LTC3212.
An internal counter and decoder selects the output con-
figuration from the number of pulses. This counter is
clocked by the rising edges of the LEDEN signal. Refer to
Figure 2 for timing details. The outputs are programmed
using Table 1.
Table 1. LED Programming
PULSES
R
G
B
1
0
0
1
2
0
1
0
3
0
1
1
4
1
0
0
5
1
0
1
6
1
1
0
7+
White Mode
Mode Switching
The LTC3212 will automatically switch from 1x to 2x mode
whenever it detects a LED driver is entering dropout. The
part will wait approximately 140µs before switching to 2x
mode. This delay will act as filtering to prevent the part
from incorrectly switching to 2x mode due to a momen-
tary glitch on the V_IN supply. The mode may be reset by
entering shutdown mode and reprogramming.
LEDEN
LED
CURRENT
SHUTDOWN
t_PWH ≥ 80ns
t_SD
350µs
t_PWL ≥ 80ns
t_EN
400µs
PROGRAMMED
CURRENT
3212 F02
Figure 2. LED Selection and Shutdown Timing Diagram
3212fb