DLPA3000 Datasheet, PDF (25/75 Pages) Texas Instruments – PMIC and High-Current LED Driver IC

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DLPA3000
DLPS052 – OCTOBER 2015
Feature Description (continued)
Table 1. Switch Positions for Common Anode RGB LEDs
PINS CH_SEL[1:0
00
01
10
11
P
Open
Closed
Open
Open
SWITCH
Q
Open
Open
Closed
Open
R
Open
Open
Open
Closed
IDAC REGISTER
N/A
0x03 and 0x04 SW1_IDAC[9:0]
0x05 and 0x06 SW2_IDAC[9:0]
0x07 and 0x08 SW3_IDAC[9:0]
Besides enabling one of the switches, CH_SEL[1:0] also selects a 10-bit current setting for the control IDAC that
is used as the set current for the LED. This set current together with the measured current through R_LIM is used
to control the illumination driver to the appropriate V_LED. The current through the 3 LEDs can be set
independently by registers 0x03 to 0x08 (Table 1).
Each current level can be set from off to 150mV/R_LIM in 1023 steps:
Led current(A) 0 for bit value 0
Led current(A) ^{Bit value  1} ˜ ^150mV for bit value 1 to 1023
1024
R_LIM
(5)
The maximum current for R_LIM= 25 mΩ is thus 6 A.
7.3.2.4.1 Break Before Make (BBM)
The switching of the three LED NMOS switches (P, Q, and R) is controlled such that a switch is returned to the
OPEN position first before the subsequent switch is set to the CLOSED position (BBM). (See Figure 9.) The
dead time between opening and closing switches is controlled through the BBM register (0x0E). Switches that
already are in the CLOSED position and are to remain in the CLOSED state are not opened during the BBM
delay time.
BBM dead time (0x0E)
P
Q
R
P
Figure 9. BBM Timing
7.3.2.4.2 Openloop Voltage
Several situations exist in which the control loop for the buck converter via the LED is not present. In order to
prevent the output voltage of the buck converter to run-away, the loop is closed by means of an internal resistive
divider (see Figure 5 - Openloop feedback circuitry). Situations in which the openloop voltage control is active:
• During the BBM period. Transitions from one LED to another implies that during the BBM time all LEDs are
off.
• Current setting for all three LEDs is 0.
It is advised to set the openloop voltage to about the lowest LED forward voltage. The openloop voltage can be
set between 3 V and 18 V in steps of 1 V through register 0x18.
Copyright © 2015, Texas Instruments Incorporated
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