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General Description

The MAX6968 serial-interfaced LED driver provides

eight open-drain, constant-current sinking LED driver

outputs rated at 5.5V. The MAX6968 operates from a 3V

to 5.5V supply. The MAX6968 supply and the LEDs’

supply or supplies may power up in any order. The

constant-current outputs are programmed together to

up to 55mA using a single external resistor. The

MAX6968 operates with a 25Mb, industry-standard, 4-

wire serial interface.

The MAX6968 uses the industry-standard shift-register-

plus-latch-type serial interface. The driver accepts data

shifted into an 8-bit shift register using data input DIN

and clock input CLK. Input data appears at the output

DOUT eight clock cycles later to allow cascading of

multiple MAX6968s. The latch-enable input LE loads

the 8 bits of shift register data into an 8-bit output latch

to set which LEDs are on and which are off. The output-

enable input OE gates all eight outputs on and off, and

is fast enough to be used as a PWM input for LED

intensity control.

For applications requiring LED fault detection, refer to

the MAX6977 data sheet that automatically detects

open-circuit LEDs.

For safety-related applications requiring a watchdog

timer, refer to the MAX6978 data sheet that includes a

fail-safe feature that blanks the display if the serial inter-

face becomes inactive for more than 1s.

The MAX6968 is one of a family of 12 shift-register-plus-

latch-type LED drivers. The family includes 8-port and

16-port types, with 5.5V- or 36V-rated LED outputs, with

and without open-circuit LED detection and watchdog.

All versions operate from a 3V to 5.5V supply, and are

specified over the -40°C to +125°C temperature range.

Features

♦ 25Mb Industry-Standard 4-Wire Serial Interface at 5V

♦ 3V to 5.5V Logic Supply

♦ 8 Constant-Current LED Outputs Rated at 5.5V

♦ Up to 55mA Continuous Current per Output

♦ Output Current Programmed by Single Resistor

♦ 3% Current Matching Between Outputs

♦ 6% Current Matching Between ICs

♦ -40°C to +125°C Temperature Range

MAX6968

8-Port, 5.5V Constant-Current LED Driver

________________________________________________________________ Maxim Integrated Products 1

GND

V+

SET

DOUT

OUT7

OUT6

OUT5

OUT4

TOP VIEW

MAX6968AUE

MAX6968APE

MAX6968AAE

TSSOP/PDIP/SSOP

DIN

CLK

OUT1

OUT0

OUT2

OUT3

Pin Configuration

Ordering Information

19-3555; Rev 2; 7/05

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Typical Application Circuit and Selector Guide appear at

end of data sheet.

Applications

Variable Message Signs

Marquee Displays

Point-of-Order Signs

Traffic Signs

Gaming Features

Architectural Lighting

PART TEMP RANGE PIN-PACKAGE

MAX6968AUE

-40°C to +125°C

16 TSSOP-EP*

MAX6968APE

-40°C to +125°C

16 PDIP

MAX6968AAE

-40°C to +125°C

16 SSOP

*EP = Exposed pad.

Summary of content (13 pages)

PAGE 1
9-3555; Rev 2; 7/05 8-Port, 5.5V Constant-Current LED Driver Features The MAX6968 serial-interfaced LED driver provides eight open-drain, constant-current sinking LED driver outputs rated at 5.5V. The MAX6968 operates from a 3V to 5.5V supply. The MAX6968 supply and the LEDs’ supply or supplies may power up in any order. The constant-current outputs are programmed together to up to 55mA using a single external resistor. The MAX6968 operates with a 25Mb, industry-standard, 4wire serial interface.
PAGE 2
MAX6968 8-Port, 5.5V Constant-Current LED Driver ABSOLUTE MAXIMUM RATINGS Voltage (with respect to GND) V+ ............................................................................-0.3V to +6V OUT_ .......................................................................-0.3V to +6V DIN, CLK, LE, OE, SET ................................-0.3V to (V+ + 0.3V) DOUT Current ..................................................................±10mA OUT_ Sink Current ................................................
PAGE 3
8-Port, 5.5V Constant-Current LED Driver (Typical Operating Circuit, V+ = 4.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.
PAGE 4
3.3V TIMING CHARACTERISTICS (Typical Operating Circuit, V+ = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.
PAGE 5
8-Port, 5.5V Constant-Current LED Driver TA = -40°C 6 TA = +25°C 3 20 TA = +25°C TA = +85°C 15 TA = +125°C 10 5 0 3.5 4.0 4.5 5.0 5.5 MAX6968 toc06 50 TA = -40°C 40 TA = +25°C TA = +85°C 30 TA = +125°C 20 10 0 3.0 0 0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 SUPPLY VOLTAGE (V) PORT OUTPUT VOLTAGE (V) PORT OUTPUT VOLTAGE (V) PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 720Ω, V+ = 5.0V) PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 360Ω, V+ = 5.
PAGE 6
8-Port, 5.5V Constant-Current LED Driver MAX6968 Pin Description PIN NAME 1 GND Ground 2 DIN Serial-Data Input. Data is loaded into the internal 8-bit shift register on CLK’s rising edge. 3 CLK Serial-Clock Input. Data is loaded into the internal 8-bit shift register on CLK’s rising edge. 4 LE 5–12 OUT0–OUT7 13 OE Output-Enable Input. High forces outputs OUT0–OUT7 to high impedance, without altering the contents of the output latches.
PAGE 7
8-Port, 5.5V Constant-Current LED Driver The MAX6968 LED driver comprises a 4-wire serial interface driving eight constant-current sinking opendrain output ports. The outputs drive LEDs in either static or multiplex applications (Figure 1). The constantcurrent 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 (0.5V to 2.5V).
PAGE 8
-Port, 5.5V Constant-Current LED Driver MAX6968 CLK is the serial-clock input, which shifts data at DIN into the MAX6968 8-bit shift register on its rising edge. LE LE is the load input of the MAX6968 latch that transfers data from the MAX6968 8-bit shift register to its 8-bit latch when LE is high (transparent latch), and latches the data on the LE’s falling edge of LE (Figure 2). The fourth input provides output-enable control of the output drivers.
PAGE 9
8-Port, 5.5V Constant-Current LED Driver Selecting External Component RSET to Set LED Output Current The MAX6968 uses an external resistor RSET to set the LED current for outputs OUT0–OUT7. The minimum allowed value of RSET is 307.6Ω, which sets the output currents to 55mA. The maximum allowed value of RSET is 1.5kΩ. The reference value, 360Ω, sets the output currents to 50mA. To set a different output current, use the formula: RSET = 18,000 / IOUT where IOUT is the desired output current in mA.
PAGE 10
8-Port, 5.5V Constant-Current LED Driver MAX6968 Selector Guide NO. OF OUTPUTS PART MAX OUTPUT VOLTAGE (V) MAX OUTPUT CURRENT MAX6968 8 MAX6977 5.5 LED FAULT DETECTION WATCHDOG — — Yes — MAX6978 Yes Yes MAX6970 — — 8 MAX6981 36 MAX6980 55mA MAX6969 16 MAX6984 5.
PAGE 11
8-Port, 5.5V Constant-Current LED Driver TSSOP 4.4mm BODY.EPS XX XX PACKAGE OUTLINE, TSSOP, 4.40 MM BODY, EXPOSED PAD 21-0108 E 1 1 ______________________________________________________________________________________ 11 MAX6968 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.
PAGE 12
Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) PDIPN.EPS MAX6968 8-Port, 5.
PAGE 13
8-Port, 5.5V Constant-Current LED Driver SSOP.EPS 2 1 INCHES E H MILLIMETERS DIM MIN MAX MIN MAX A 0.068 0.078 1.73 1.99 A1 0.002 0.008 0.05 0.21 B 0.010 0.015 0.25 0.38 C 0.20 0.09 0.004 0.008 SEE VARIATIONS D E e 0.205 0.212 0.0256 BSC 5.20 MILLIMETERS INCHES D D D D D 5.38 MIN MAX MIN MAX 0.239 0.239 0.278 0.249 0.249 0.289 6.07 6.07 7.07 6.33 6.33 7.33 0.317 0.397 0.328 0.407 8.07 10.07 8.33 10.33 N 14L 16L 20L 24L 28L 0.65 BSC H 0.301 0.311 7.