MAXIM MAX6968 User Manual

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, 4­wire serial interface.

The MAX6968 uses the industry-standard shift-register­plus-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 output­enable 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 inter­face becomes inactive for more than 1s.

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

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

GND

V+

SET

DOUT

OE

OUT7

OUT6

OUT5

OUT4

TOP VIEW

MAX6968AUE
MAX6968APE
MAX6968AAE

TSSOP/PDIP/SSOP

DIN

CLK

OUT1

LE

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

16 TSSOP-EP*

MAX6968APE

16 PDIP

MAX6968AAE

16 SSOP

*EP = Exposed pad.

-40°C to +125°C

-40°C to +125°C

-40°C to +125°C

MAX6968

8-Port, 5.5V Constant-Current LED Driver

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

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 .............................................................60mA

Total GND Current ...........................................................480mA

Continuous Power Dissipation (TA= +70°C)

16-Pin SSOP (derate 7.1mW/°C above +70°C) ............571mW

16-Pin PDIP (derate 10.5mW/°C above +70°C)............842mW

16-Pin TSSOP (derate 21.3mW/°C over

TA= +70°C) ..............................................................1702mW

Operating Temperature Range .........................-40°C to +125°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS

(Typical Operating Circuit, V+ = 3V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V+ = 5V, TA= +25°C.)

(Note 1)

PARAMETER

CONDITIONS

UNITS

Operating Supply Voltage V+ 3.0 5.5 V

Output Voltage V

OUT

5.5 V

Standby Current
(Interface Idle, All Output Ports
High Impedance, R

SET

= 360Ω)

I

+

All logic inputs at V+ or GND, DOUT
unloaded

4.5 5.6 mA

Standby Current
(Interface Running, All Output
Ports High Impedance,
R

SET

= 360Ω)

I

+

f

CLK

= 5MHz, OE = V+, DIN and LE = V+

or GND, DOUT unloaded

4.7 6 mA

Supply Current
(Interface Idle, All Output Ports
Active Low, R

SET

= 360Ω)

I

+

All logic inputs at V+ or GND,
DOUT unloaded

10 25 mA

Input High Voltage
DIN, CLK, LE, OE

V

IH

V

Input Low Voltage
DIN, CLK, LE, OE

V

IL

V

Hysteresis Voltage
DIN, CLK, LE, OE

∆V

I

0.8 V

Input Leakage Current
DIN, CLK, LE, OE

I

IH

, I

IL

-1 +1 µA

Output High-Voltage DOUT V

OH

I

SOURCE

= 4mA

V +

V

Output Low Voltage V

OL

I

SINK

= 4mA 0.5 V

Output Current OUT_ I

OUT

V+ = 3V to 5.5V, V

OUT

= 0.5V to 2.5V,

R

SET

= 360Ω

42 50 56 mA

Output Leakage Current OUT_ I

LEAK

OE = V+, V

OUT

= V+ 1 µA

Watchdog Timeout t

WD

1s

SYMBOL

MIN TYP MAX

0.7 V+

- 0.5V

0.3 V+

MAX6968

8-Port, 5.5V Constant-Current LED Driver

_______________________________________________________________________________________ 3

5V TIMING CHARACTERISTICS

(Typical Operating Circuit, V+ = 4.5V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

CLK Clock Period t

CP

40 ns

CLK Pulse-Width High t

CH

19 ns

CLK Pulse-Width Low t

CL

19 ns

DIN Setup Time t

DS

4ns

DIN Hold Time t

DH

8ns

DOUT Propagation Delay t

DO

12 32 ns

DOUT Rise and Fall Time

C

DOUT

= 10pF, 20% to 80% 10 ns

LE Pulse-Width High t

LW

20 ns

LE Setup Time t

LS

10 ns

LE Rising to OUT_ Rising Delay t

LRR

(Note 2) 100 ns

LE Rising to OUT_ Falling Delay t

LRF

(Note 2) 280 ns

CLK Rising to OUT_ Rising Delay

t

CRR

(Note 2) 100 ns

CLK Rising to OUT_ Falling Delay

t

CRF

(Note 2) 310 ns

OE Rising to OUT_ Rising Delay

t

OEH

100 ns

OE Falling to OUT_ Falling Delay

t

OEL

300 ns

LED Output OUT_ Turn-On Fall
Time

t

f

80% to 20% 200 ns

LED Output OUT_ Turn-Off Rise
Time

t

r

20% to 80% 120 ns

SYMBOL

t

DR, tDF

MIN TYP MAX

MAX6968

8-Port, 5.5V Constant-Current LED Driver

4 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

3.3V TIMING CHARACTERISTICS

(Typical Operating Circuit, V+ = 3V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

CLK Clock Period t

CP

52 ns

CLK Pulse-Width High t

CH

24 ns

CLK Pulse-Width Low t

CL

24 ns

DIN Setup Time t

DS

4ns

DIN Hold Time t

DH

8ns

DOUT Propagation Delay t

DO

12 48 ns

DOUT Rise and Fall Time

C

DOUT

= 10pF, 20% to 80% 10 ns

LE Pulse-Width High t

LW

20 ns

LE Setup Time t

LS

15 ns

LE Rising to OUT_ Rising Delay t

LRR

100 ns

LE Rising to OUT_ Falling Delay t

LRF

310 ns

CLK Rising to OUT_ Rising Delay

t

CRR

100 ns

CLK Rising to OUT_ Falling Delay

t

CRF

330 ns

OE Rising to OUT_ Rising Delay

t

OEH

100 ns

OE Falling to OUT_ Falling Delay

t

OEL

330 ns

LED Output OUT_ Turn-On Fall
Time

t

f

80% to 20% 200 ns

LED Output OUT_ Turn-Off Rise
Time

t

r

20% to 80% 120 ns

Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: See Figure 3.

SUPPLY CURRENT vs. SUPPLY VOLTAGE

(INTERFACE IDLE, ALL OUTPUTS OFF,

R

SET

= 720Ω)

MAX6968 toc01

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

5.04.53.5 4.0

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

2.6

3.0 5.5

TA = +125°C

TA = +85°C

TA = -40°C

TA = +25°C

4.2

4.5

4.4

4.3

4.6

4.7

4.8

4.9

5.0

5.1

5.2

3.0 4.03.5 4.5 5.0 5.5

MAX6968 toc02

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

TA = +125°C

TA = +85°C

TA = -40°C

SUPPLY CURRENT vs. SUPPLY VOLTAGE

(INTERFACE IDLE, ALL OUTPUTS

OFF, R

SET

= 360Ω)

TA = +25°C

0

3

9

6

12

15

3.0 4.03.5 4.5 5.0 5.5

MAX6968 toc03

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

SUPPLY CURRENT vs. SUPPLY VOLTAGE

(INTERFACE IDLE, ALL OUTPUTS

ON, R

SET

= 720Ω)

TA = +125°C

TA = +85°C

TA = +25°C

TA = -40°C

SYMBOL

MIN TYP MAX

t

DR, tDF