Integrated 8-Channel LED Drivers with

Switch-Mode Boost and SEPIC Controller

______________________________________________________________________________________

17

LED Fault Detection (MAX16808)

The MAX16808 includes circuitry that detects open-cir-

cuit LEDs automatically. An open-circuit fault occurs

when an output is sinking current less than approxi-

mately 50% of the programmed current flows. Open cir-

cuits are checked just after the falling edge of OE. The

fault data is latched on the rising edge of LE and is

shifted out when new LED data is loaded into the out-

put latches from the shift register. If one or more output

ports are detected with an open-circuit fault, the D6

and D5 bits of DOUT go high. If no open-circuit faults

are detected, D6 and D5 are set to low. The data in the

other 6 bit positions in DOUT are not altered. Fault sta-

tus is shifted out on DOUT for the first two rising edges

of the clock after the falling edge of LE (see Figure 5).

LE is normally taken high after all 8 bits of new LED

D0

D7

D7

LE

CLK

DIN

DOUT

OE

OUT_

80%

20%

Figure 3. 4-Wire Serial-Interface Timing Diagram

LE

OUT_

LE

OUT_

CLK

OUT_

CLK

OUT_

Figure 4. LE and CLK to OUT_ Timing

OE

LE

CLK

DOUT

D7

D6

D5

D4

FAULT STATUS BITS

Figure 5. Fault Timing