Ver2.1

17

LD1024

16-Channel, Constant-Current LED Driver with LED Open Detection

SETTING FOR THE CONSTANT SINK CURRENT VALUE

X 68

(6)

where:

V(REXT) = the internal reference voltage on the REXT pin (typically 1.20 V)

Iout must be set in the range of 5 mA to 45 mA. The constant sink current characteristic for the external resistor

value is shown in Figure 10. Table 1 describes the constant current output versus external resistor value.

Iout(mA, Typical)

45

1.8K

40

2.0K

35

2.3K

30

2.7K

25

3.2K

20

4.0K

15

5.4K

10

8.0K

5

16K

Table 1. Constant Current Output versus External Resistor Value

CONSTANT CURRENT DRIVER ON/OFF CONTROL

When OEB is low, the corresponding output is turned on if the data in the on/off control data latch are '1' and

remains off if the data are '0'. When OEB is high, all outputs are forced off. This control is shown in Table 2.

ON/OFF CONTROL LATCH DATA

CONSTANT CURRENT OUTPUT STATUS

0

Off

1

On

Table 2. On/Off Control Data Truth Table

When the IC is initially powered on, the data in the on/off control shift register and data latch are not set to the

respective default value. Therefore, the on/off control data must be written to the data latch before turning the

constant current output on. OEB should be at a high level when powered on because the constant current

may be turned on as a result of random data in the on/off control latch.

The on/off data corresponding to any unconnected OUTn outputs should be set to ‘0’ before turning on the

remaining outputs. Otherwise, the supply current (ICC) increases while the LEDs are on.