Detailed Description

The MAX6971 LED driver comprises a 4-wire serial

interface driving 16 constant-current-sinking, open-

drain output ports. The outputs drive LEDs in either

static or multiplex applications (Figure 1). The constant-

current outputs are guaranteed for current accuracy

not only with chip-supply voltage variations (5V ±10%

and 3V to 5.5V), but also over a realistic range of driver

output voltage drop (0.8V to 2.5V). The drivers use cur-

rent-sensing feedback circuitry (not simple current mir-

rors) to ensure very small current variations over the full

allowed range of output voltage (see the Typical

Operating Characteristics).

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

register 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 current

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 36V, independent of the MAX6971 supply, V+. The

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

4-Wire Serial Interface

The serial interface on the MAX6971 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 MAX6971. 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.

16-Port, 36V Constant-Current LED Driver

_______________________________________________________________________________________

7

.

D15

D14

D1

D0

D7

LE

CLK

DIN

DOUT

OE

OUT_

80%

20%

Figure 2. 4-Wire Serial-Interface Timing Diagram