TLC5904

LED DRIVER

SLLS391 – NOVEMBER 1999

12

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

constant current output selection by user (80 mA

× 16 bits or 120 mA × 8 bits)

When the MODE terminal is set to high, output is selected as 80 mA

× 16 bits. When the MODE terminal is set

to low, output is selected as 120 mA

× 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 an LED such as OUT0-to-OUT1 and OUT2-to-OUT3 because they operate in a pair when the 8 bits output

mode is selected. Also, in this case, the current value of the constant current output is the same as the 16 bits

output mode. Therefore, when an output current of 120 mA is desired, the resister connected to the IREF

terminal should be selected to the same value as the output current of 60 mA.

Table 1. Operation Mode Selection

MODE

OUTPUT

H

80 mA

× 16 bits

L

120 mA

× 8 bits

On the constant current output terminals (OUT0–15), approximately 37 times the current which flows through

using the following equation:

where BCENA is low.

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

constant output current operation

The constant current output turns on the sink constant current if all the gray scale data in 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, the output counted corresponding to 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 constant current output number of the gray scale. Accordingly, during the on-state of constant

current output, the XLATCH should be kept to 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 output unconnected. Unless this action is taken,

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

the constant current output light 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 a shift register, DCLK and DIN are utilized. The selection of a shift register will be done

by RSEL0 and RSEL1 as shown in below table. Note that RSEL0 and RSEL1 should be changed when both

DCLK and XLATCH are low.

Table 2. Shift Register Latch Selection

RSEL0

RSEL1

SHIFT REGISTER LATCH SELECTED

L

L

Shift register latch for gray scale data

L

H

Shift register latch for brightness control

H

L

Shift register latch for OVM

H

H

N/A (DOUTn is tied to low level)