TLC5905 Datasheet, PDF(12/27 Page) Texas Instruments

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TLC5905 Datasheet, PDF (12/27 Pages) Texas Instruments – LED DRIVER

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TLC5905

LED DRIVER

SLLS401 â NOVEMBER 1999

PRINCIPLES OF OPERATION

constant current output selection by user (80 mA x16 bits or 120 mA x 8 bits)

When the MODE terminal is set to high, output is selected as 80 mA x 16 bits. When the MODE terminal is set

to low, output is selected as 120 mA x 8 bits. By this setting, the shift register latch for gray scale data is changed

to the configuration corresponding to the bit selected. Note that two constant output terminals should be tied

to LED such as OUT0-to-OUT1 and OUT2-to-OUT3 because they operate in pairs when the 8-bit output mode

is selected. Also, in this case, the current value on constant current output is the same as in 16-bit output mode.

Therefore, when output current of 120 mA is desired, the resister connected to the IREF terminal should be set

to the same value as the output current of 60 mA.

Table 1. Operation Mode Selection

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ MODE

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ H

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ L

OUTPUT

80 mA Ã 16 bits

120 mA Ã 8 bits

On the constant current output terminals (OUT0â15), approximately 37 times the current that flows through

external resistor, RIREF (connected between IREF and GND), can flow. The external resistor value is calculated

using the following equation.

R(IREF) (â¦) â 37 Ã 1.24 (V) / IOL(C)(A) where BCENA is low.

Note that more current flows if IREF is connected directly to GND.

constant output current operation

The constant current output turns on (sink constant current), if all the gray scale data latched into the gray scale

latch is not zero on the falling edge of the gray scale clock after the next rising edge of the gray scale clock when

BLANK goes from high to low. After that, the number of the falling edge is counted by the 8-bit gray scale counter.

Then, output counted corresponding to the gray scale data is turned off (stop to sink constant current). If the

shift register for gray scale is updated during XLATCH high, data on the gray scale data latch is also updated

affecting the number of the gray scale of constant current output. Accordingly, during on-state of constant

current output, XLATCH should be kept at a low level and the gray scale data latch should be held. If there are

constant current output terminals unconnected (includes LED disconnection), the LED should be turned on after

writing zero to the gray scale data latch corresponding to the output unconnected. Unless this action is taken,

supply current on the constant current driver will increase resulting in influencing the current value for the

constant current output when turned on.

shift register latch

The device provides three kinds of shift register latchs including the gray scale data, brightness control, and

OVM. To write data into the shift register, SCLK and SIN are utilized. The selection of the shift register will be

done by RSEL0 and RSEL1 as shown in Table 2. Note that RSEL0 and RSEL1 should be changed when both

SCLK and XLATCH are low.

Table 2. Shift Register Latch Selection

RSEL0

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ L

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ H

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ H