TLC5904

LED DRIVER

SLLS391 – NOVEMBER 1999

15

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

brightness control function

By writting data into the brightness control latch, the current on all constant current outputs can be adjusted to

control the variation of brightness between ICs and the division ratio for the gray scale clock can be set to control

the variation of brigtness for the total panel system.

output current adjustment on all constant current outputs – brightness adjustment between ICs

By using the lower 5 bits of the brightness control latch, the output current can be adjusted to 32 steps. 1 step

is 1.6% of the current ratio between 100% and 51.6% when the set output current is 100% by an external resistor.

By using this function, the brightness control between modules (ICs) can be adjusted sending desired data

externally even if ICs are mounted on print-circuit board. When BCENA is pulled low, output current is set to

100%.

Table 3. Relative Current Ratio For Total Constant Current Output

CODE

CURRENT RATIO (%)

20 (mA)

80 (mA)

VIREF (TYP)

MSB 00000 LSB

51.6

10.3

41.3

0.63

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

11110

98.4

19.7

78.7

1.22

11111†

100

20.0

80.0

1.24

† BCENA is low.

frequency division ratio setting for gray scale clock – panel brightness adjustment

By using the upper 3 bits of the brightness control latch, the gray scale clock can be divided into a frequency

division ratio of 1/1 to 1/8. If the gray scale clock is set to 8 times the speed (256x8=2048) of frequency during

horizontal scanning time, the brightness can be adjusted to 8 steps selecting the frequency division ratio. By

using this function, the total panel brightness can be adjusted at once, and it applies to the brightness of day

or night circumstances. When BCENA is pulled low, the gray scale clock is not divided. When BCENA is pulled

high, the brightness can be adjusted (see Table 4).

Table 4. Relative Brightness Ratio For Total Constant Current Output

CODE

FREQUENCY

DIVISION RATIO

RELATIVE BRIGHTNESS RATIO

(%)

MSB 000 LSB†

1/1

12.5

.

.

.

.

.

.

.

.

.

.

.

.

110

1/7

87.5

111

1/8

100

† BCENA is low.

OVM (output voltage monitor) function

By writing data into the OVM latch, the comparison voltage for the voltage comparator of OUT0 to OUT15 can

be set, and the output signal for XDOWN1 and XDOWN2 can be checked.