MAX6983 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX6983

16-Port, 36V Constant-Current LED Driver with LED Fault Detection and Watchdog

Maxim Integrated 

16-Port, 36V Constant-Current LED Driver with

LED Fault Detection and Watchdog

LE

tLRF

OUT_

LE

tLRR

OUT_

CLK

tCRF

OUT_

CLK

tCRR

OUT_

Figure 3. LE and CLK to OUT_ Timing

The fourth input provides output-enable control of the out-

put drivers. OE is high to force outputs OUT0–OUT15

high impedance, without altering the contents of the out-

put latches, and low to enable outputs OUT0–OUT15 to

follow the state of the output latches.

OE is independent of the operation of the serial inter-

face. Data can be shifted into the serial-interface shift

register and latched regardless of the state of OE.

DOUT is the serial-data output, which shifts data out

from the MAX6983’s 16-bit shift register on the rising

edge of CLK. Data at DIN is propagated through the

shift register and appears at DOUT 16 clock cycles later.

See Figure 2.

Watchdog

The MAX6983 includes a watchdog circuit that monitors

the CLK, DIN, and LE inputs. If there is no transition on

any one of these inputs for nominally 1s, the output

latches are cleared and outputs OUT0–OUT15 go high

impedance like the initial power-up condition. This turns

off all LEDs connected to the outputs. The shift-register

data does not change, just the output-latch data.

The watchdog is intended to be used as a fail-safe fea-

ture for applications that prefer a blank display to an

incorrect display if the serial interface fails. When the

watchdog triggers, the outputs remain off until the dri-

ver output latches are updated with data turning them

OE

LE

CLK

DOUT

Figure 4. Fault Timing

D15 D14 D13 D12

FAULT STATUS BITS

on. Recovery is therefore automatic if the transmission

failure is temporary because the MAX6983 does not

lock up in the watchdog timeout state. The MAX6983

operates correctly when the serial interface is next acti-

vated, and the watchdog circuit is reset and starts

monitoring the serial interface again. The watchdog

function requires no software change to the application

driving the MAX6983.

LED Fault Detection

The MAX6983 includes circuitry that detects open-cir-

cuit LEDs automatically. An open-circuit fault occurs

when an output is programmed to sink current but less

than about 50% of the programmed current flows.

Open circuits 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 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 when the next data

transmission is shifted in after the rising edge of LE. LE

is normally taken high after all 16 bits of new LED data

have been clocked into the shift register(s), and then

DOUT outputs data bit D15. On the next two rising

edges of CLK, the 2 fault status bits, D14 and D13, are

clocked out in that order, followed by the remaining 13

unchanged data bits D12 to D0.

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 integri-

ty. Bits D13 and D14 are checked first to see that they

contain the same data (validating the status) and sec-

ond, whether faults are reported or not by the actual

logic level.

Figure 4 is the LE and CLK to OUT_ timing diagram.

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