General Description
The MAX6977 serial-interfaced LED driver provides
eight open-drain, constant-current sinking LED driver
outputs rated at 5.5V. The MAX6977 operates from a 3V
to 5.5V supply. The MAX6977 supply and the LEDs’
supply may power up in any order. The constant-current outputs are programmed together to up to 55mA
using a single external resistor. The MAX6977 operates
with a 25Mb, industry-standard, 4-wire serial interface.
The MAX6977 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 MAX6977 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 MAX6977s. 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 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 MAX6977 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
♦ Reports Open-Circuit LED Faults
♦ -40°C to +125°C Temperature Range
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
________________________________________________________________ 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
MAX6977AUE
MAX6977APE
MAX6977AAE
TSSOP/PDIP/SSOP
DIN
CLK
OUT1
LE
OUT0
OUT2
OUT3
Pin Configuration
Ordering Information
19-3554; 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
MAX6977AUE
16 TSSOP-EP*
MAX6977APE
16 PDIP
MAX6977AAE
16 SSOP
*EP = Exposed pad.
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
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 above +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 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+ = 4.5V to 5.5V, V
OUT
= 0.8V 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+
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
_______________________________________________________________________________________ 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 Pulse Width (Fault-Detection
Data Valid)
t
LF
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
tDR, t
DF
MIN TYP MAX
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
4 _______________________________________________________________________________________
3.3V TIMING CHARACTERISTICS
(Typical Operating Circuit, V+ = 3V to 5.5V, TA= T
MIN
to T
MAX
, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
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 Pulse Width (Fault-Detection
Data Valid)
t
LW
20 ns
LE Setup Time t
LS
15 ns
LE Rising to OUT_ Rising Delay 100 ns
LE Rising to OUT_ Falling Delay 310 ns
CLK Rising to OUT_ Rising Delay
100 ns
CLK Rising to OUT_ Falling Delay
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.
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
R
SET
= 720Ω)
MAX6977 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
TA = +125°C TA = +85°C
TA = -40°C
TA = +25°C
4.0
4.3
4.2
4.1
4.4
4.5
4.6
4.7
4.8
4.9
5.0
3.0 4.03.5 4.5 5.0 5.5
MAX6977 toc02
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
R
SET
= 360Ω)
TA = +125°C
TA = +85°C
TA = -40°C
TA = +25°C
0
3
9
6
12
15
3.0 4.03.5 4.5 5.0 5.5
MAX6977 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 = -40°C
TA = +25°C
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
0
3
9
6
12
15
3.0 4.03.5 4.5 5.0 5.5
MAX6977 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 = -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+ = 3.3V)
MAX6977 toc05
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = -40°C
TA = +25°C
TA = +85°C
TA = +125°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)
MAX6977 toc06
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = -40°C
TA = +25°C
TA = +85°C
TA = +125°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)
MAX6977 toc07
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = -40°C
TA = +25°C
TA = +85°C
TA = +125°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)
MAX6977 toc08
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = -40°C
TA = +25°C
TA = +85°C
TA = +125°C
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)
MAX6977 toc09
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = -40°C
TA = +25°C
52
51
50
49
48
3.0 4.0
3.5
4.5 5.0 5.5
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (R
SET
= 360Ω, V
OUT
= 2V)
MAX6977 toc10
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = -40°C
TA = +25°C
0
10
30
20
40
50
0 1000500 1500 2000 2500
PORT OUTPUT CURRENT
vs. SET RESISTANCE
MAX6977 toc11
SET RESISTANCE (Ω)
PORT OUTPUT CURRENT (mA)
Detailed Description
The MAX6977 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). 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 Typical Operating
Characteristics).
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
6 _______________________________________________________________________________________
PIN NAME FUNCTION
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.
4LE
Load-Enable Input. Data is loaded transparently from the internal shift register to the output latch while
LE is high. Data is latched into the output latch on LE's falling edge, and retained while LE is low.
5–12
LED Driver Outputs. OUT0–OUT7 are open-drain, constant-current sinking outputs rated to 5.5V.
13 OE
O utp ut E nab l e Inp ut. H i g h for ces outp uts OUT0–OUT7 to hi g h i m p ed ance, w i thout al ter i ng the contents
of the outp ut l atches. Low enab l es outp uts OUT0–OUT7 to fol l ow the state of the outp ut l atches.
14 DOUT
Serial-Data Output. Data is clocked out of the 8-bit internal shift register to DOUT on CLK’s rising edge.
15 SET LED Current Setting. Connect SET to GND through a resistor (R
SET
) to set the maximum LED current.
16 V+ Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor.
PAD
Exposed pad on package underside. Connect to GND.
Pin Description
SERIAL-TO-PARALLEL SHIFT REGISTER
LATCHES
OUT0
OUT1
OUT2
DOUT
DIN
CLK
OUT7
CONSTANT-CURRENT SINKS
OUT5
OUT6
POWER-ON
RESET
V+
CURRENT
REFERENCE
V+
OE
GND
GND
LE
D0 D7
D0 D7
D0 D7
R
SET
MAX6977
FAULT DETECTION
Figure 1. MAX6977 Block Diagram
*TSSOP package only.
OUT0–OUT7
E xp osed p ad *
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
_______________________________________________________________________________________ 7
The 4-wire serial interface comprises an 8-bit shift register and an 8-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 8-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 MAX6977 supply, V+. The
constant-current capability is up to 55mA per output,
set for all eight outputs by an external resistor, R
SET
.
Initial Power-Up and Operation
An internal reset circuit clears the internal registers of
the MAX6977 on power-up. All outputs OUT0 to OUT7,
therefore, initialize high impedance, and the interface
output DOUT initializes low, regardless of the initial
logic levels of the CLK, DIN, OE, and LE inputs.
4-Wire Serial Interface
The serial interface on the MAX6977 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 MAX6977. The serial interface data
word length is 8 bits, D0–D7.
The functions of the five interface pins follow. DIN is the
serial-data input, and must be stable when it is sam-
pled on the rising edge of CLK (Table 1). Data is shifted in MSB first. This means that data bit D7 is clocked
in first, followed by 7 more data bits finishing with the
LSB D0.
CLK is the serial clock input, which shifts data at DIN
into the MAX6977 8-bit shift register on its rising edge.
LE is the load input of the MAX6977 latch, which transfers data from the MAX6977 8-bit shift register to its 8bit latch when LE is a high (transparent latch), and
latches the data on the LE falling edge of LE (Figure 2).
The rising edge of LE loads fault data into the MAX6977
8-bit shift register, replacing bits D6 and D5 with fault
data. This fault data is automatically shifted out through
DOUT when the next display data is shifted in.
The fourth input provides output enable control of the
output drivers. OE is high to force outputs OUT0 to
OUT7 high impedance, without altering the contents of
the output latches, and low to enable outputs OUT0 to
OUT7 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 MAX6977’s 8-bit shift register on the rising edge
of CLK. Data at DIN is propagated through the shift register and appears at DOUT eight clock cycles later.
LED Fault Detection
The MAX6977 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.
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
L = Low-logic level
H = High-logic level
X = Don’t care
P = Present state
R = Previous state
INPUT
D
CLK
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
D
LE
0D1D2
——————
——————
——————
R0R1R2— R
P0P1P2… P
XXX… XX
… D
n-1Dn
n-1Rn
n-1Pn
INPUT
D0D1D2… D
— ————
—————
—————
—————
P0P1P2… P
Hi-Z Hi-Z Hi-Z … Hi-Z
n-1
n-1
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
8 _______________________________________________________________________________________
Figure 2. 4-Wire Serial Interface Timing Diagram
LE
OUT_
LE
OUT_
CLK
OUT_
CLK
OUT_
t
CRR
t
CRF
t
LRR
t
LRF
Figure 3. LE and CLK to OUT_ Timing
.
D7 D6
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
LF
t
CH
D1 D0
D7
LE
CLK
DIN
DOUT
OE
OUT_
80%
20%
Open circuits are checked just after the rising edge of
LE, when new LED data is loaded into the output latches from the shift register(s). If one or more output port is
detected with an open-circuit fault, then the 2 bits, D6
and D5, in the serial interface shift register are both set
high. If no open-circuit faults are detected, then D6 and
D5 are both cleared low. The data in other 6-bit positions in the serial interface shift register is not altered.
Fault status is automatically shifted out on DOUT when
the next data transmission is shifted in. LE is normally
taken high after all 8 bits of new LED data have been
clocked into the shift register, and so at that time,
DOUT is outputting data bit D7. On the next two rising
edges of CLK, the 2 fault status bits, D6 and D5, are
clocked out in that order, followed by the remaining 5
unchanged data bits D4 to D0.
A typical fault-detecting application tests all the shiftedout data. Bits D0–D4 and D7 are checked against the
originally transmitted data to check data link integrity.
Bits D5 and D6 are checked first to see that they contain the same data (validating the status), and second
whether faults are reported by the actual logic level.
The fault status bit identifies which driver chip has at
least one open-circuit LED. It is possible to determine
how many LEDs driven by a chip are at fault by running
eight test patterns, each of which lights a different single LED. The fault status bit then effectively identifies
only one output at a time.
Applications Information
Selecting External Component R
SET
to
Set LED Output Current
The MAX6977 uses an external resistor R
SET
to set the
LED current for outputs OUT0–OUT7. The minimum
allowed value of R
SET
is 307.6Ω, 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
= 18000 / I
OUT
where I
OUT
is the desired output current in mA.
Computing Power Dissipation
The upper limit for power dissipation (PD) for the
MAX6977 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 MAX6977 outputs driving LEDs at the
same time (maximum is 8)
V
OUT
= MAX6977 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 = 8, DUTY = 1, V
OUT
= 2V, V+ = 5.25V
PD= (5.25V x 25mA) + (2V x 1 x 47mA x 8) = 0.883W
Thus, for a 16-pin TSSOP package (TJA= 1 / 0.0213 =
+46.95°C/W from Absolute Maximum Ratings), the
maximum allowed ambient temperature TAis given by:
T
J(MAX)
= TA+ (PDx TJA) = +150°C = TA+
(0.883 x 46.95°C/W)
so TA= +108.5°C.
Overtemperature Cutoff
The MAX6977 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 will be 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 MAX6977 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 MAX6977 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 MAX6977s. The
necessary capacitance depends on the LED load current, PWM switching frequency, and serial interface
speed. Inadequate V+ decoupling may cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
For the TSSOP version, connect the underside exposed
pad to GND.
Chip Information
TRANSISTOR COUNT: 2382
PROCESS: BiCMOS
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
_______________________________________________________________________________________ 9
µC
MOSI
OUT0
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
SCLK
DIN
CLK
0V
GND
MISO DOUT
0V
360Ω
OEENABLE
+5V
V+
5V
LATCHLOAD
SET
MAX6977
Typical Application Circuit
Selector Guide
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
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
10 ______________________________________________________________________________________
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
______________________________________________________________________________________ 11
TSSOP 4.4mm BODY.EPS
E
1
1
21-0108
PACKAGE OUTLINE, TSSOP, 4.40 MM BODY,
EXPOSED PAD
XX XX
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
.)
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
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
MAX6977
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
SSOP.EPS
PACKAGE OUTLINE, SSOP, 5.3 MM
1
1
21-0056
C
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
NOTES:
1. D&E DO NOT INCLUDE MOLD FLASH.
2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006").
3. CONTROLLING DIMENSION: MILLIMETERS.
4. MEETS JEDEC MO150.
5. LEADS TO BE COPLANAR WITHIN 0.10 MM.
7.90
H
L
0
0.301
0.025
8
0.311
0.037
0
7.65
0.63
8
0.95
MAX
5.38
MILLIMETERS
B
C
D
E
e
A1
DIM
A
SEE VARIATIONS
0.0256 BSC
0.010
0.004
0.205
0.002
0.015
0.008
0.212
0.008
INCHES
MIN
MAX
0.078
0.65 BSC
0.25
0.09
5.20
0.05
0.38
0.20
0.21
MIN
1.73 1.99
MILLIMETERS
6.07
6.07
10.07
8.07
7.07
INCHES
D
D
D
D
D
0.239
0.239
0.397
0.317
0.278
MIN
0.249
0.249
0.407
0.328
0.289
MAX
MIN
6.33
6.33
10.33
8.33
7.33
14L
16L
28L
24L
20L
MAX
N
A
D
e
A1
L
C
HE
N
12
B
0.068
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
.)
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