19-3703; Rev 1; 12/10
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
General Description
The MAX6979 serial-interfaced LED driver provides 16
open-drain, constant-current-sinking LED driver outputs
rated at 5.5V. The MAX6979 operates from a 3V to 5.5V
supply. The MAX6979 supply and the LEDs’ supply can
power up in any order. The constant-current outputs
are programmed together to up to 55mA using a single
external resistor. The MAX6979 operates with a 25Mb,
industry-standard, 4-wire serial interface.
The MAX6979 includes circuitry that automatically
detects open-circuit LEDs. Fault status is loaded into the
serial-interface shift register when LE goes high and is
automatically shifted out on DOUT when the next data
transmission is shifted in.
The MAX6979 includes a fail-safe feature for safety-
related applications, which blanks the display if the ser-
ial interface fails. If the serial interface becomes
inactive for more than 1s, all driver output latches are
automatically cleared. This turns off all LEDs connected
to the outputs. The shift register data is not disturbed.
The outputs remain off until the driver output latches are
updated with data turning them on, so recovery is auto-
matic if the transmission failure is temporary. The
watchdog function requires no software change to the
application driving the MAX6979.
The MAX6979 uses the industry-standard shift-register-
plus-latch-type serial interface. The driver accepts data
shifted into a 16-bit shift register using data input DIN
and clock input CLK. Input data appears at the output
DOUT 16 clock cycles later to allow cascading of multi-
ple MAX6979s. The latch-enable input, LE, loads the 16
bits of shift-register data into a 16-bit output latch to set
which LEDs are on and which are off. The output-
enable input,
OE,
gates all 16 outputs on and off, and is
fast enough to be used as a PWM input for LED intensi-
ty control.
The MAX6979 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.
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Features
25Mb Industry-Standard, 4-Wire Serial Interface at 5V
3V to 5.5V Logic Supply
16 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
Watchdog Clears Display if Interface Fails
Reports Open-Circuit LED Faults
High-Dissipation, 24-Pin Packages
-40°C to +125°C Temperature Range
MAX6979
Ordering Information
PART
MAX6979AUG+
TEMP RANGE
-40°C to +125°C
PIN-PACKAGE
24 TSSOP
MAX6979APG+
-40°C to +125°C
24 PDIP
+Denotes
a lead(Pb)-free/RoHS-compliant package.
Typical Application Circuit and Selector Guide appear at
end of data sheet.
Pin Configuration
TOP VIEW
GND 1
DIN 2
CLK 3
LE 4
OUT0 5
OUT1 6
OUT2 7
OUT3 8
OUT4 9
OUT5 10
OUT6 11
OUT7 12
+
24 V+
23 SET
22 DOUT
21 OE
20 OUT15
19 OUT14
MAX6979AUG
MAX6979APG
18 OUT13
17 OUT12
16 OUT11
15 OUT10
14 OUT9
13 OUT8
Applications
Variable Message Signs
Marquee Displays
Point-of-Order Signs
Traffic Signs
Gaming Features
Architectural Lighting
TSSOP/PDIP
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
MAX6979
ABSOLUTE MAXIMUM RATINGS
Voltage (with respect to GND)
V+ .............................................................................-0.3V to +6V
OUT_ ........................................................................-0.3V to +6V
DIN, CLK, LE,
OE,
SE ..................................-0.3V to (V+ + 0.3V)
DOUT_ Current .................................................................±10mA
OUT_ Sink Current ..............................................................60mA
Total GND Current ............................................................960mA
Continuous Power Dissipation (T
A
= +70°C)
24-Pin PDIP (derate 13.3mW/°C over +70°C)............1067mW
24-Pin TSSOP (derate 12.2mW/°C over +70°C) .........975mW
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
Soldering Temperature (reflow)
Lead(Pb)-free packages..............................................+260°C
Packages containing lead(Pb).....................................+240°C
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.
ELECTRICAL CHARACTERISTICS
(Typical
Operating Circuit,
V+ = 3V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at V+ = 5V, T
A
= +25°C.)
(Note 1)
PARAMETER
Operating Supply Voltage
Output Voltage
Standby Current
(Interface Idle, All Output Ports
High Impedance, R
SET
= 360Ω)
Standby Current
(Interface Running, All Output
Ports High Impedance,
R
SET
= 360Ω)
Supply Current
(Interface Idle, All Output Ports
Active Low, R
SET
= 360Ω)
Input High Voltage
DIN, CLK, LE,
OE
Input Low Voltage
DIN, CLK, LE,
OE
Hysteresis Voltage
DIN, CLK, LE,
OE
Input Leakage Current
DIN, CLK, LE,
OE
Output High Voltage DOUT
Output Low Voltage
Output Current OUT
Output Leakage Current OUT
Watchdog Timeout
SYMBOL
V+
V
OUT
I
+
All logic inputs at V+ or GND, DOUT
unloaded
5.7
CONDITIONS
MIN
3.0
TYP
MAX
5.5
5.5
8
UNITS
V
V
mA
I
+
f
CLK
= 5MHz,
OE
= V+, DIN and LE = V+
or GND, DOUT unloaded
6
8.5
mA
I
+
All logic inputs at V+ or GND,
DOUT unloaded
0.7 x
V+
18
25
mA
V
IH
V
IL
∆V
I
I
IH
, I
IL
V
OH
V
OL
I
OUT
I
LEAK
t
WD
I
SOURCE
= 4mA
I
SINK
= 4mA
V+ = 3V to 5.5V, V
OUT
= 0.5V to 2.5V,
R
SET
= 360Ω
OE
= V+, V
OUT
= V+
V
0.3 x
V+
0.8
V
V
+1
µA
V
0.5
V
mA
µA
s
-1
V+
- 0.5V
37
50
61
1
0.1
1
2.5
2
_______________________________________________________________________________________
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
5V TIMING CHARACTERISTICS
(Typical
Operating Circuit,
V+ = 4.5V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Notes 1 and 2)
PARAMETER
CLK Clock Period
CLK Pulse-Width High
CLK Pulse-Width Low
DIN Setup Time
DIN Hold Time
DOUT Propagation Delay
DOUT Rise and Fall Time
LE Setup Time
LE Rising to OUT Rising Delay
LE Rising to OUT Falling Delay
CLK Rising to OUT Rising Delay
CLK Rising to OUT Falling Delay
OE
Rising to OUT Rising Delay
OE
Falling to OUT Falling Delay
LED Output OUT Turn-On Fall
Time
LED Output OUT Turn-Off Rise
Time
SYMBOL
t
CP
t
CH
t
CL
t
DS
t
DH
t
DO
t
DR
, t
DF
t
LS
t
LRR
t
LRF
t
CRR
t
CRF
t
OEH
t
OEL
t
f
t
r
80% to 20%; pullup resistor = 65Ω
20% to 80%; pullup resistor = 65Ω
(Note 2)
(Note 2)
(Note 2)
(Note 2)
C
DOUT
= 10pF, 20% to 80%
10
100
300
100
310
100
320
120
120
CONDITIONS
MIN
40
19
19
4
8
12
32
10
TYP
MAX
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
MAX6979
_______________________________________________________________________________________
3
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
MAX6979
3.3V TIMING CHARACTERISTICS
(Typical
Operating Circuit,
V+ = 3V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Notes 1 and 2)
PARAMETER
CLK Clock Period
CLK Pulse-Width High
CLK Pulse-Width Low
DIN Setup Time
DIN Hold Time
DOUT Propagation Delay
DOUT Rise and Fall Time
LE Setup Time
LE Rising to OUT Rising Delay
LE Rising to OUT Falling Delay
CLK Rising to OUT Rising Delay
CLK Rising to OUT Falling Delay
OE
Rising to OUT Rising Delay
OE
Falling to OUT Falling Delay
LED Output OUT Turn-On Fall
Time
LED Output OUT Turn-Off Rise
Time
t
OEH
t
OEL
t
f
t
r
80% to 20%
20% to 80%
t
LS
SYMBOL
t
CP
t
CH
t
CL
t
DS
t
DH
t
DO
C
DOUT
= 10pF, 20% to 80%
15
120
310
120
330
120
330
120
120
CONDITIONS
MIN
52
24
24
4
8
12
50
12
TYP
MAX
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Note 1:
All parameters tested at T
A
= +25°C. Specifications overtemperature are guaranteed by design.
Note 2:
See Figure 3.
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
R
SET
= 720Ω)
MAX6979 toc01
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
R
SET
= 360Ω)
MAX6979 toc02
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS ON,
R
SET
= 720Ω)
T
A
= +125°C
18
SUPPLY CURRENT (mA)
16
14
12
10
8
6
T
A
= +25°C
T
A
= -40°C
T
A
= +85°C
MAX6979 toc03
4.50
4.25
SUPPLY CURRENT (mA)
4.00
3.75
3.50
3.25
3.00
2.75
2.50
6.0
5.8
5.6
SUPPLY CURRENT (mA)
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
T
A
= -40°C
T
A
= +25°C
T
A
= +125°C
T
A
= +85°C
20
T
A
= +125°C
T
A
= +85°C
T
A
= -40°C
T
A
= +25°C
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
4
_______________________________________________________________________________________
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS ON, R
SET
= 360Ω)
T
A
= +125°C
T
A
= +85°C
MAX6979 toc04
MAX6979
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 720Ω, V+ = 3.3V)
MAX6979 toc05
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 360Ω, V+ = 3.3V)
MAX6979 toc06
22
20
SUPPLY CURRENT (mA)
18
16
14
12
10
3.0
3.5
4.0
4.5
5.0
T
A
= +25°C
30
25
T
A
= -40°C
20
15
10
5
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
60
50
40
30
20
10
0
T
A
= -40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
PORT OUTPUT CURRENT (mA)
T
A
= -40°C
0
5.5
0
0.5
1.0
1.5
2.0
2.5
3.0
SUPPLY VOLTAGE (V)
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
0
0.5
1.0
1.5
2.0
2.5
3.0
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 720Ω, V+ = 5.0V)
MAX6979 toc07
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 360Ω, V+ = 5.0V)
MAX6979 toc08
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (R
SET
= 720Ω, V
OUT
= 2V)
MAX6979 toc09
30
25
20
15
10
5
0
0
0.5
1.0
1.5
2.0
2.5
T
A
= -40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
60
50
T
A
= -40°C
40
30
20
10
0
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
27.0
26.5
T
A
= -40°C
26.0
25.5
T
A
= +85°C
25.0
24.5
24.0
T
A
= +125°C
T
A
= +25°C
PORT OUTPUT CURRENT (mA)
PORT OUTPUT CURRENT (mA)
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
PORT OUTPUT CURRENT (mA)
3.0
3.5
4.0
4.5
5.0
5.5
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (R
SET
= 360Ω, V
OUT
= 2V)
MAX6979 toc10
PORT OUTPUT CURRENT
vs. R
SET
RESISTANCE (V+ = 5.0V)
MAX6979 toc11
54
50
PORT OUTPUT CURRENT (mA)
PORT OUTPUT CURRENT (mA)
53
T
A
= -40°C
52
T
A
= +25°C
40
30
51
T
A
= +125°C
T
A
= +85°C
20
50
10
49
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
0
0
300
600
900
1200
1500
R
SET
RESISTANCE (Ω)
_______________________________________________________________________________________
5
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