MAX6979 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX6979

16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog

Maxim Integrated 

16-Port, 5.5V Constant-Current LED Driver with

LED Fault Detection and Watchdog

LE

CLK

DIN

DOUT

tCL

tCH

tDH

tDS

D15

D14

tLW

tLF

tLS

tCP

D1

tDO

D0

D15

OE

OUT_

tOEW

tOEL

tOEH

80%

.

20%

tf

tr

Figure 2. 4-Wire Serial-Interface Timing Diagram

The 4-wire serial interface comprises a 16-bit shift reg-

ister and a 16-bit transparent latch. The shift register is

written through a clock input CLK and a data input DIN

and the data propagates to a data output DOUT. The

data output allows multiple drivers to be cascaded and

operated together. The contents of the 16-bit shift reg-

ister are loaded into the transparent latch through a

latch-enable input LE. The latch is transparent to the

shift register outputs when high, and latches the cur-

rent state on the falling edge of LE.

Each driver output is an open-drain, constant-current

sink that should be connected to the cathode of either

a single LED or a series string of multiple LEDs. The

LED anode can be connected to a supply voltage of up

to 5.5V, independent of the MAX6979 supply, V+. The

constant-current capability is up to 55mA per output,

set for all 16 outputs by an external resistor, RSET.

4-Wire Serial Interface

The serial interface on the MAX6979 is a 4-wire serial

interface using four inputs (DIN, CLK, LE, OE) and a

data output (DOUT). This interface is used to write dis-

play data to the MAX6979. The serial-interface data

word length is 16 bits, D0–D15. See Figure 2.

The functions of the five interface pins are as follows.

DIN is the serial-data input, and must be stable when it

is sampled on the rising edge of CLK. Data is shifted

in, MSB first. This means that data bit D15 is clocked in

first, followed by 15 more data bits, finishing with the

LSB D0.

CLK is the serial-clock input, which shifts data at DIN

into the MAX6979 16-bit shift register on its rising edge.

LE is the latch load input of the MAX6979, which trans-

fers data from the MAX6979 16-bit shift register to its 16-

bit latch when LE is high (transparent latch), and latches

the data on the falling edge of LE (Figure 2).

The fourth input provides output-enable control of the

output drivers. OE is high to force outputs

OUT0–OUT15 high impedance, without altering the

contents of the output latches, and low to enable out-

puts 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 MAX6979’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.

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