Page 1
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 safetyrelated applications, which blanks the display if the serial 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 automatic 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-registerplus-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 multiple 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 outputenable input, OE, gates all 16 outputs on and off, and is
fast enough to be used as a PWM input for LED intensity control.
The MAX6979 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
♦ 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
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
________________________________________________________________ Maxim Integrated Products 1
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
V+
SET
DOUT
OELE
CLK
DIN
GND
TOP VIEW
OUT15
OUT14
OUT13
OUT12OUT3
OUT2
OUT1
OUT0
16
15
14
13
9
10
11
12
OUT11
OUT10
OUT9
OUT8OUT7
OUT6
OUT5
OUT4
TSSOP/PDIP
MAX6979AUG
MAX6979APG
Pin Configuration
Ordering Information
19-3703; Rev 0; 5/05
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
PINPACKAGE
PK G
C O D E
MAX6979AUG
24 TSSOP —
MAX6979APG
24 PDIP —
-40°C to +125°C
-40°C to +125°C
Page 2
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
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, SE ..................................-0.3V to (V+ + 0.3V)
DOUT_ Current .................................................................±10mA
OUT_ Sink Current ..............................................................60mA
Total GND Current ............................................................960mA
Continuous Power Dissipation (TA= +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
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
5.7 8 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
6 8.5 mA
Supply Current
(Interface Idle, All Output Ports
Active Low, R
SET
= 360Ω)
I
+
All logic inputs at V+ or GND,
DOUT unloaded
18 25 mA
Input High Voltage
DIN, CLK, LE, OE
V
IH
0.7 x
V+
V
Input Low Voltage
DIN, CLK, LE, OE
V
IL
0.3 x
V+
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
37 50 61 mA
Output Leakage Current OUT I
LEAK
OE = V+, V
OUT
= V+ 1 µA
Watchdog Timeout t
WD
0.1 1 2.5 s
SYMBOL
MIN TYP MAX
- 0.5V
Page 3
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 3
5V TIMING CHARACTERISTICS
(Typical Operating Circuit, V+ = 4.5V to 5.5V, TA= T
MIN
to T
MAX
, unless otherwise noted.) (Notes 1, 2)
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 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) 300 ns
C LK Ri si ng to O U T Ri si ng D el ay t
CRR
(Note 2) 100 ns
C LK Ri si ng to O U T Fal l i ng D el ay t
CRF
(Note 2) 310 ns
OE Rising to OUT Rising Delay t
OEH
100 ns
OE Falling to OUT Falling Delay t
OEL
320 ns
LED Output OUT Turn-On Fall
Time
t
f
80% to 20%; pullup resistor = 65Ω 120 ns
LED Output OUT Turn-Off Rise
Time
t
r
20% to 80%; pullup resistor = 65Ω 120 ns
SYMBOL
tDR, t
DF
MIN TYP MAX
Page 4
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
4 _______________________________________________________________________________________
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
R
SET
= 720Ω)
MAX6979 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.04.53.5 4.0
2.75
3.00
3.25
3.50
3.75
4.00
4.25
4.50
2.50
3.0 5.5
TA = +125°C
TA = +85°C
TA = -40°C
TA = +25°C
4.0
4.6
4.4
4.2
4.8
5.0
5.2
5.4
5.6
5.8
6.0
3.0 4.03.5 4.5 5.0 5.5
MAX6979 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
6
8
16
14
12
10
18
20
3.0 4.03.5 4.5 5.0 5.5
MAX6979 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
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.) (Notes 1, 2)
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 50 ns
DOUT Rise and Fall Time C
DOUT
= 10pF, 20% to 80% 12 ns
LE Setup Time t
LS
15 ns
LE Rising to OUT Rising Delay 120 ns
LE Rising to OUT Falling Delay 310 ns
C LK Ri si ng to O U T Ri si ng D el ay 120 ns
C LK Ri si ng to O U T Fal l i ng D el ay 330 ns
OE Rising to OUT Rising Delay t
OEH
120 ns
OE Falling to OUT Falling Delay t
OEL
330 ns
LED Output OUT Turn-On Fall
Time
t
f
80% to 20% 120 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.
SYMBOL
MIN TYP MAX
Page 5
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 5
10
12
16
14
22
20
18
3.0 4.03.5 4.5 5.0 5.5
MAX6979 toc04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS ON, R
SET
= 360Ω)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
10
5
20
15
25
30
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 720Ω, V+ = 3.3V)
MAX6979 toc05
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
20
10
40
30
50
60
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 360Ω, V+ = 3.3V)
MAX6979 toc06
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = -40°C
TA = +25°C
0
10
5
20
15
25
30
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 720Ω, V+ = 5.0V)
MAX6979 toc07
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
20
10
40
30
50
60
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (R
SET
= 360Ω, V+ = 5.0V)
MAX6979 toc08
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
27.0
26.5
26.0
25.5
25.0
24.5
24.0
3.0 4.0
3.5
4.5 5.0 5.5
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (R
SET
= 720Ω, V
OUT
= 2V)
MAX6979 toc09
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
54
53
52
51
50
49
3.0 4.0
3.5
4.5 5.0 5.5
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (R
SET
= 360Ω, V
OUT
= 2V)
MAX6979 toc10
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
10
30
20
40
50
0 600300 900 1200 1500
PORT OUTPUT CURRENT
vs. R
SET
RESISTANCE (V+ = 5.0V)
MAX6979 toc11
R
SET
RESISTANCE (Ω)
PORT OUTPUT CURRENT (mA)
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
Page 6
Detailed Description
The MAX6979 LED driver comprises a 4-wire serial
drain 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). The drivers use current-sensing feedback circuitry (not simple current mirrors) to ensure very small current variations over the full
allowed range of output voltage (see the Typical
Operating Characteristics).
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 GND Ground
2 DIN Serial-Data Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.
3 CLK Serial-Clock Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.
4LE
Load-Enable Input. Data is loaded transparently from the internal shift register(s) to the output latch(es)
5–20
OUT0–
LED Driver Outputs. OUT0 to OUT15 are open-drain, constant-current-sinking outputs rated to 5.5V.
21 OE
Output Enable Input. High forces outputs OUT0 to OUT15 high impedance without altering the contents of
the output latches. Low enables outputs OUT0 to OUT15 to follow the state of the output latches.
22 DOUT Serial-Data Output. Data is clocked out of the 16-bit internal shift register to DOUT on CLK’s rising edge.
23 SET LED Current Setting. Connect SET to GND through a resistor (R
SET
) to set the maximum LED current.
24 V+ Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor.
Figure 1. Block Diagram
while LE is high. Data is latched into the output latch(es) on LE's falling edge, and retained while LE is low.
OUT15
CLK
MAX6979
SERIAL-TO-PARALLEL SHIFT REGISTER
DIN
LE
OE
D0 D15
D0 D15
D0 D15
LATCHES
CONSTANT-CURRENT SINKS
POWER-ON
RESET
WATCH-
DOG
V+
CURRENT
REFERENCE
DOUT
V+
OUT0
OUT1
FAULT DETECTION
OUT2
OUT13
OUT14
OUT15
GND
GND
R
SET
interface driving 16 constant-current sinking open-
Page 7
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 7
The 4-wire serial interface comprises a 16-bit shift register 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 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, R
SET
.
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 display 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 transfers data from the MAX6979 16-bit shift register to its 16bit 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 outputs OUT0–OUT15 to
follow the state of the output latches.
OE is independent of the operation of the serial interface. 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.
Figure 2. 4-Wire Serial-Interface Timing Diagram
.
D15 D14
t
DS
t
DH
t
CL
t
CP
t
DO
t
OEW
t
OEL
t
f
t
r
t
OEH
t
LS
t
LW
t
CH
D1 D0
D15
LE
CLK
DIN
DOUT
OE
OUT_
80%
20%
t
LF
Page 8
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
8 _______________________________________________________________________________________
Watchdog
The MAX6979 includes a watchdog circuit that monitors
the CLK, DIN, and LE inputs. If there is no transition on
any one of these inputs for nominally 1s, then the output
latches are cleared and outputs OUT0–OUT15 go high
impedance like the initial power-up condition. This turns
off all LEDs connected to the outputs. The shift-register
data does not change, just the output-latch data.
The watchdog is intended to be used as a fail-safe feature for applications that prefer a blank display to an
incorrect display if the serial interface fails. When the
watchdog triggers, the outputs remain off until the driver output latches are updated with data turning them
on. Recovery is therefore automatic if the transmission
failure is temporary, because the MAX6979 does not
lock up in the watchdog timeout state. The MAX6979
operates correctly when the serial interface is next activated, and the watchdog circuit is reset and starts
monitoring the serial interface again. The watchdog
function requires no software change to the application
driving the MAX6979.
LED Fault Detection
The MAX6979 includes circuitry that detects open-circuit LEDs automatically. An open-circuit fault occurs
when an output is programmed to sink current but less
than about 50% of the programmed current flows.
Open circuits are checked just after the falling edge of
OE. The fault data is latched on the rising edge of LE and
is shifted out when new LED data is loaded into the output latches from the shift register. If one or more output
ports are detected with an open-circuit fault, the D14 and
D13 bits of DOUT go high. If no open-circuit faults are
detected, D14 and D13 are set to low. The data in the
other 14 bit positions in DOUT are not altered.
Fault status is shifted out on DOUT when the next data
transmission is shifted in after the rising edge of LE. LE
is normally taken high after all 16 bits of new LED data
have been clocked into the shift register(s), and then
DOUT outputs data bit D15. On the next two rising
edges of CLK, the 2 fault status bits, D14 and D13, are
clocked out in that order, followed by the remaining 13
unchanged data bits D12 to D0.
A typical fault-detecting application tests all the shifted
out data. Bits D0–D12 and D15 are checked against
the originally transmitted data to check data-link integrity. Bits D13 and D14 are checked first to see that they
contain the same data (validating the status) and second, whether faults are reported or not by the actual
logic level.
Figure 4 is the LE and CLK to OUT_ timing diagram.
Applications Information
Selecting External Component R
SET
to
Set LED Output Current
The MAX6979 uses an external resistor R
SET
to set the
LED current for outputs OUT0–OUT15. The minimum
allowed value of R
SET
is 327.3Ω, which sets the output
currents to 55mA. The maximum allowed value of R
SET
is 1.5kΩ. The reference value, 360Ω, sets the output
currents to 50mA. To set a different output current, use
the formula:
R
SET
= 18,000 / I
OUT
where I
OUT
is the desired output current in mA.
LE
OUT_
LE
OUT_
CLK
OUT_
CLK
OUT_
t
CRR
t
CRF
t
LRR
t
LRF
Figure 3. LE and CLK to OUT_ Timing
OE
LE
CLK
DOUT
D15
D14
D13
D12
FAULT STATUS BITS
Figure 4. Fault Timing Diagram
Page 9
Computing Power Dissipation
The upper limit for power dissipation (PD) for the
MAX6979 is determined from the following equation:
PD= (V+ x I+) + (V
OUT
x DUTY x I
OUT
x N)
where:
V+ = supply voltage
I+ = operating supply current when sinking I
OUT
LED
drive current into N outputs
DUTY = PWM duty cycle applied to OE
N = number of MAX6979 outputs driving LEDs at the
same time (maximum is 16)
V
OUT
= MAX6979 port output voltage when driving load
LED(s)
I
OUT
= LED drive current programmed by R
SET
PD= power dissipation, in mW if currents are in mA
Dissipation example:
I
OUT
= 47mA, N = 16, DUTY = 1,
V
OUT
= 2V, V+ = 5.25V
PD= (5.25V x 25mA) + (2V x 1 x 47mA x 16) = 1.776W
Thus, for a 24-pin TSSOP package (TJA= 1 / 0.0122 =
+82°C/W from the Absolute Maximum Ratings), the
maximum allowed ambient temperature TAis given by:
T
J(MAX)
= TA+ (PDx TJA) = +150°C =
TA+ (1.776 x 82°C/W)
so T
A
= +145.6°C.
Overtemperature Cutoff
The MAX6979 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds approximately +165°C. The outputs are
enabled again when the die temperature drops below
approximately +140°C. Register contents are not affected, so when a driver is overdissipating, the external
symptom is the load LEDs cycling between on and off as
the driver repeatedly overheats and cools, alternately
turning the LEDs off and then back on again.
Power-Supply Considerations
The MAX6979 operates with a chip supply V+, and one
or more LED supplies. Bypass each supply to GND
with a 0.1µF capacitor as close to the MAX6979 as possible. This is normally adequate for static LED driving.
For multiplex or PWM applications, it is necessary to
add an additional bulk electrolytic capacitor of 4.7µF or
more to each supply for every 4 to 16 MAX6979s. The
necessary capacitance depends on the LED load current, PWM switching frequency, and serial interface
speed. Inadequate V+ decoupling can cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 9
L = Low-logic level; H = High-logic level; X = Don’t care; P = Present state; R = Previous state.
SHIFT-REGISTER
CONTENTS
LATCH CONTENTS OUTPUT CONTENTS
SERIAL
DATA
INPUT
DIN
CLOCK
LOAD
BLANKING
OE
D
n
H
—
—
—
L
—
—
—
X
—
—
—
——
H
—
—
——
L
L
P
n
——
—
H
Hi-Z
Table 1. 4-Wire Serial-Interface Truth Table
INPUT
CLK
D
0D1D2
HR1R2…R
LR1R2…R
R0R1R2…R
XXX…XX
P1P2P3…P
————— —
…D
n-1Dn
n-2Rn-1
n-2Rn-1
n-1Rn
n-1Pn
INPUT
LE
D
0D1D2
——————
——————
——————
R0R1R2—R
P0P1P2…P
XXX…XX
…D
n-1Pn
n-1Dn
n-1Rn
INPUT
D0D1D2…D
— ————
— ————
— ————
— ————
P0P1P2… P
Hi-Z Hi-Z Hi-Z … Hi-Z
n-1
n-1
Page 10
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
10 ______________________________________________________________________________________
PART
NO. OF
OUTPUTS
MAX OUTPUT
VOLTAGE (V)
MAX OUTPUT
CURRENT
LED FAULT
DETECTION
WATCHDOG
MAX6968 ——
MAX6977 Yes —
MAX6978
8 5.5
Yes Yes
MAX6970* ——
MAX6981* Yes —
MAX6980*
836
Yes Yes
MAX6969 ——
MAX6984* Yes —
MAX6979
16 5.5
Yes Yes
MAX6971* ——
MAX6982* Yes —
MAX6983*
16 36
55mA
Yes Yes
Selector Guide
Typical Application Circuit
µC
MOSI
OUT0
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
SCLK
DIN
CLK
0V
GND
MISO DOUT
360Ω
OEENABLE
+5V
V+
+5V
LATCHLOAD
SET
MAX6979
OUT8
OUT9
OUT10
OUT11
OUT12
OUT13
OUT14
OUT15
Chip Information
PROCESS: BiCMOS
*Future product—contact factory for availability
Page 11
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
______________________________________________________________________________________ 11
TSSOP4.40mm.EPS
PACKAGE OUTLINE, TSSOP 4.40mm BODY
21-0066
1
1
G
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
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
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
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