MAX16809_07 Datasheet, PDF (18/23 Pages) Maxim Integrated Products – Integrated 16-Channel LED Drivers with Switch-Mode Boost and SEPIC Controller

Integrated 16-Channel LED Drivers with
Switch-Mode Boost and SEPIC Controller
LED Fault Detection (MAX16810)
The MAX16810 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 shift-
ed out when new LED data is loaded into the output
latches from the shift register. If one or more output
ports are detected with an open-circuit fault, the D14
and D13 bits of DOUT go high. If no open-circuit faults
are detected, D14 and D13 are set to low. The data in
the other 14 bit positions in DOUT are not altered. Fault
status 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 16 bits of
new LED data have been clocked into the shift regis-
ter(s), and then DOUT outputs data bit D15. A typical
fault-detecting application tests all the shifted out data.
Bits D0–D12 and D15 are checked against the originally
transmitted data to check data-link integrity. Bits D13
and D14 are checked first to see that they contain the
same data (validating the status), and second, whether
faults are reported or not by the actual logic level.
OE
LE
CLK
DOUT
Figure 5. Fault Timing
D15 D14 D13 D12
FAULT STATUS BITS
Selecting External Component
R_SET to Set LED Output Current
The MAX16809/MAX16810 use an external resistor,
R_SET, to set the LED current for outputs OUT0–OUT15.
The minimum allowed value of R_SET is 311Ω, which
sets the output currents to 55mA. The maximum
allowed value of R_SET is 5kΩ (I_{OUT_ _} = 3.6mA) and
maximum allowed capacitance at SET is 100pF.
Use the following formula to set the output current:
R_SET
=
17,100V
I_{OUT _ _}
where I_{OUT_ _} is the desired output current in milliamps
and the value for R_SET is in ohms.
Overtemperature Cutoff
The MAX16809/MAX16810 contain an internal tempera-
ture sensor that turns off all outputs when the die temper-
ature exceeds +165°C. The outputs are enabled again
when the die temperature drops below +140°C. Register
contents are not affected, so when a driver is overdissi-
pating, the external symptom is the load LEDs cycling on
and off as the driver repeatedly overheats and cools,
alternately turning itself off and then back on again.
Stand-Alone Operation
In stand-alone operation, the MAX16809/MAX16810
does not use the 4-wire interface (see the Typical
Operating Circuits). Connect DIN and LE to V+ and
provide at least 16 external clock pulses to CLK to
enable 16 output ports. This startup pulse sequence
can be provided either using an external clock or the
PWM signal. The external clock can also be generated
using the signal at RTCT and an external comparator.
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