LP3952 datasheet(13/46 Pages) TI1

13 / 46 page

LP3952

www.ti.com

SNVS518A – JULY 2007 – REVISED MARCH 2013

100 - internal current mirror multiplier

RRGB- resistor value in Ohms

Ω - internal resistor in the IRGB input

For example if 22mA is required for maximum RGB current RRGB equals to:

RRGB=100×1.23V / IMAX–50Ω=123V / 0.022A–50Ω=5.54kΩ

(2)

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 programming is shown in table below. The

default value after reset is 00b.

IR1[1:0], IG1[1:0],

Maximum

IB1[1:0], IR2[1:0],

Current/Output

IG2[1:0], IB2[1:0]

0.25 × IMAX

0.50 × IMAX

0.75 × IMAX

1.00 × IMAX

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 increased.

Please note that the switch mode requires an external ballast 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).

Table 1. RGB_ctrl Register (00H) (1.65V

≤ VDDIO ≤ VDD1,2V) (unless otherwise noted)

R1, G1 and B1 are switches

→ limit current with ballast resistor

CC_RGB1

bit7

R1, G1 and B1 are constant current sinks, current limited internally

R2, G2 and B2 are switches

→ limit current with ballast resistor

CC_RGB2

bit6

R2, G2 and B2 are constant current sinks, current limited internally

R1 is on

r1sw

bit5

R1 is off

G1 is on

g1sw

bit4

G1 is off

B1 is on

b1sw

bit3

B1 is off

R2 is on

r2sw

bit2

R2 is off

G2 is on

g2sw

bit1

G2 is off

B2 is on

b2sw

bit0

B2 is off

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