19-0555; Rev 0; 5/06
24-Output PWM LED Drivers
for Message Boards
General Description
The MAX6974/MAX6975 precision current-sinking,
24-output PWM LED drivers drive red, green, and blue
LEDs for full-color graphic message boards and video
displays. Each output has an individual 12-bit (MAX6974)
or 14-bit (MAX6975) PWM-intensity (hue) control and
7-bit (MAX6974) or 5-bit (MAX6975) global PWM intensity
(luminance) control. The MAX6974/MAX6975 feature a
high-speed, fully buffered cascadable serial interface,
open-circuit LED fault detection circuitry, as well as a
watchdog timer.
The driver has three banks of eight outputs, with each
bank intended to drive a different color in RGB applica-
tions. The full-scale current for each bank of eight out-
puts is adjustable from 6mA to 30mA in 256 steps
(0.3125% per step) to calibrate each color.
The MAX6974/MAX6975 can optionally multiplex by
using outputs
MUX0
and
MUX1,
which each drive an
external pnp transistor. Multiplexing doubles the
MAX6974/MAX6975 drive capability to 48 LEDs.
The MAX6974/MAX6975 operate from a 3.0V to 3.6V
power supply. The LED power supply can range from
3V to 7V. The LED drivers require only 0.8V headroom
above the LEDs’ forward-voltage drop. Using a sepa-
rate LED supply voltage for each LED minimizes power
consumption.
The serial interface uses differential signaling for the
high-speed clock and data signals to reduce EMI and
improve signal integrity. The MAX6974/MAX6975 buffer
all interface signals to simplify cascading devices in
modules that use a large number of drivers.
An internal watchdog timer, when enabled, automatically
clears the pixel-data registers and blanks the display if
any of the signal inputs fail to toggle within 40ms.
The MAX6974/MAX6975 are available in 40-pin TQFN
packages and operate over the -40°C to +125°C
temperature range.
Refer to the MAX6972/MAX6973 data sheet for a
16-output, 11mA to 55mA software-compatible device.
EZCascade is a trademark of Maxim Integrated Products, Inc.
Features
o
24 LED Current Sink Outputs (Three Banks of
Eight Outputs)
o
48 LED Drive Option When Multiplexing
o
33MHz Clock Supports Up to 63 Frames per
Second of Video
o
Constant Output Current Calibration from 6mA to
30mA in 256 Steps
o
EZCascade™ Interface Simplifies Multiple Driver
Cascading Without External Buffers
o
12-Bit or 14-Bit Individual PWM LED Intensity
Controls
o
7-Bit or 5-Bit Panel PWM-Intensity Control
o
+3V to +7V LED Power Supply
o
+3.0V to +3.6V Logic Supply
o
Open-Circuit LED Fault Detection
o
Optional Watchdog Timer Blanks Display if
Interface Fails
o
Standard -40°C to +125°C Operating Temperature
Range
MAX6974/MAX6975
Ordering Information
PART
MAX6974ATL+
MAX6975ATL+
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
PIN-
PACKAGE
40 TQFN-EP*
40 TQFN-EP*
PKG
CODE
T4066-3
T4066-3
*EP
= Exposed pad.
+Denotes
lead-free package.
Pin Configuration
LOADO
DOUT+
CLKO+
DOUT-
CLK0-
MUX1
G7
G6
G5
20 G4
19 G3
EP*
18 G2
17 G1
16 G0
15 R7
14 R6
13 R5
12 R4
11 R3
1
MUX0
2
CLKI+
3
CLKI-
4
DIN+
5
DIN-
6
LOADI
7
I.C.
8
R0
9
R1
10
R2
TOP VIEW
30 29 28 27 26 25 24 23 22 21
AGND 31
B7 32
B6 33
B5 34
B4 35
B3 36
B2 37
B1 38
B0 39
V
DD
40
Applications
LED Video Display Panels
LED Message Boards
Variable Message Signs (VMS)
Signs
Graphic Panels
Typical Operating Circuit appears at the end of data sheet.
MAX6974ATL/
MAX6975ATL
+
TQFN-EP
*EP = EXPOSED PADDLE.
________________________________________________________________
Maxim Integrated Products
V
DD
1
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.
24-Output PWM LED Drivers
for Message Boards
MAX6974/MAX6975
ABSOLUTE MAXIMUM RATINGS
(All voltages with respect to GND.)
V
DD
........................................................................-0.3V to +4.0V
R0–R7, G0–G7, B0–B7,
MUX0,
and
MUX1
...........-0.3V to +8.0V
All Other Pins..............................................-0.3V to (V
DD
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
40-Pin TQFN (derate 37mW/°C over +70°C) .............2963mW
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
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
(V
DD
= 3.0V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at V
DD
= 3.3V, T
A
= +85°C.) (Note 1)
PARAMETER
Operating Supply Voltage
LEDs Anode Voltage
(R0–R7, G0–G7, B0–B7,
MUX0,
and
MUX1)
SYMBOL
V
DD
V
O
f
CLKI
= 0Hz; CLKO_, DOUT_ loaded 200Ω;
calibration DACs set to 0x01
Supply Current
I
DD
f
CLKI
= 0Hz; CLKO_, DOUT_ loaded 200Ω;
calibration DACs set to 0xFF
f
CLKI
= 32MHz; CLKO_, DOUT_ loaded 200Ω;
calibration DACs set to 0xFF
Input High Voltage LOADI
Input Low Voltage LOADI
Differential Input Voltage Range
CLKI_, DIN_
Common-Mode Input Voltage
CLKI_, DIN_
Differential Input High Threshold
Differential Input Low Threshold
Differential Output Voltage
CLKO_, DOUT_
Differential Output Offset
CLKO_, DOUT_
Input Leakage Current
CLKI_, DIN_, LOADI
Input Capacitance
CLKI_, DIN_, LOADI
Output Low Voltage LOADO
Output High Voltage LOADO
V
OLC
V
OHC
I
SINK
= 5mA
I
SOURCE
= 5mA
V
DD
- 0.5
V
IHC
V
ILC
V
ID
V
CM
VDIFF
TH
VDIFF
TL
V
OD
V
OS
I
IH
, I
IL
Termination 200Ω at receiver _+ and _- inputs
Termination 200Ω at receiver _+ and _- inputs
-100
±190
1.125
-1
10
0.05
V
DD
- 0.2
0.25
1.25
±0.15
|V
ID
/ 2|
8
-8
±550
1.375
+1
0.7
x V
DD
0.3
x V
DD
±1.20
2.4
100
CONDITIONS
MIN
3.0
TYP
MAX
3.6
7
UNITS
V
V
28
51
54
52
72
77
V
V
V
V
mV
mV
mV
V
µA
pF
V
V
mA
2
_______________________________________________________________________________________
24-Output PWM LED Drivers
for Message Boards
MAX6974/MAX6975
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 3.0V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at V
DD
= 3.3V, T
A
= +85°C.) (Note 1)
PARAMETER
Output Slew Time LOADO
Output Low Voltage
MUX_
Open-Circuit Detection
Output Voltage Slew Time
R0–R7, G0–G7, B0–B7
Full-Scale Port Output Current
R0–R7, G0–G7, B0–B7
I
SINKFS
V
OLM
V
OCD
80% to 20%, load = 50pF,
calibration DACs set to 0xFF
V
DD
= 3.3V, V
O
= 1.2V,
calibration DACs set to 0xFF
T
A
= +85°C
T
A
= T
MIN
to T
MAX
T
A
= +125°C
(Note 3)
T
A
= +85°C
T
A
= -40°C
(Note 3)
28
26
±0.7
±0.7
±0.9
0.3
30
SYMBOL
I
SINK
= 40mA
200
100
32
34
2.7
2
3.3
1.15
mA/V
1.5
0.6
1.7
mA/V
2.0
%
CONDITIONS
20% to 80%, 80% to 20%, load = 10pF
MIN
TYP
3
0.4
MAX
UNITS
ns
V
mV
ns
mA
Port-to-Port Current Matching
R0–R7, G0–G7, B0–B7
ΔI
SINK
V
DD
= 3.3V, V
O
= 1.2V,
calibration DACs set to 0xFF
I
SINK
= 30mA (Note 2)
Output Load Regulation
ΔI
OLR
V
DD
= 3.3V, V
O
= 1.2V to 3.0V, T
A
= +85°C
calibration DACs set to 0x80,
T
A
= T
MIN
to T
MAX
I
SINK
= 18mA
V
DD
= 3.0 V to 3.6V, V
O
= 1.2V, T
A
= +85°C
calibration DACs set to 0x80,
T
A
= T
MIN
to T
MAX
I
SINK
= 18mA
Output Power-Supply Rejection
ΔI
OPSR
TIMING CHARACTERISTICS
(V
DD
= 3.0V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at 3.3V, T
A
= +85°C.) (Note 1)
PARAMETER
CLKI_ Input Frequency
CLKI_ Duty Cycle
CLKO_ Output Delay
DIN_ Setup Time
DIN_ Hold Time
DOUT_ Output Delay
LOADO Output Delay
LOADI Hold Time
Watchdog Period
t
PD-CLKO
t
SU-DIN
t
HD-DIN
t
PD-DOUT
t
PD-LOADO
t
HD-LOADI
When enabled
8
40
125
300
0.5
5
15
18
SYMBOL
f
CLKI
40
CONDITIONS
MIN
TYP
MAX
33
60
16
UNITS
MHz
%
ns
ns
ns
ns
ns
ns
ms
Note 1:
All parameters tested at T
A
= +85°C. Specifications over temperature are guaranteed by design.
Note 2:
Specification limits apply to devices at the same T
A
for T
A
= T
MIN
to T
MAX
.
Note 3:
Guaranteed by design.
_______________________________________________________________________________________
3
24-Output PWM LED Drivers
for Message Boards
MAX6974/MAX6975
Typical Operating Characteristics
(V
DD
= 3.3V, T
A
= +25°C, unless otherwise noted.)
OPERATING CURRENT CONSUMPTION
vs. SUPPLY VOLTAGE V
DD
MAX6974 toc01
OPERATING CURRENT CONSUMPTION
vs. SUPPLY VOLTAGE V
DD
f
CLKI
= 0MHz
CALDAC = 0x00
T
A
= -40°C
T
A
= +25°C
MAX6974 toc02
55
f
CLKI
= 32MHz
CALDAC = 0xFF
T
A
= -40°C
T
A
= +25°C
30
53
28
I
DD
(mA)
49
T
A
= +125°C
47
45
3.0
3.1
3.2
3.3
I
DD
(mA)
T
A
= +85°C
51
26
24
T
A
= +125°C
22
T
A
= +85°C
20
3.4
3.5
3.6
3.0
3.1
3.2
3.3
3.4
3.5
3.6
SUPPLY VOLTAGE V
DD
(V)
SUPPLY VOLTAGE V
DD
(V)
LED OUTPUT SINK CURRENT
vs. OUTPUT VOLTAGE
MAX6974 toc03
LED OUTPUT SINK CURRENT
vs. OUTPUT VOLTAGE
V
DD
= +3.0V
MAX6974 toc04
35
30
25
I
SINK
(mA)
20
15
10
5
0
0
T
A
= -40°C
35
30
25
I
SINK
(mA)
20
15
10
5
0
T
A
= +85°C
T
A
= +25°C
T
A
= +125°C
V
DD
= +3.3V
V
DD
= +3.6V
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
4
_______________________________________________________________________________________
24-Output PWM LED Drivers
for Message Boards
Pin Description
PIN
1
2
3
4
5
6
7
8–15
16–23
24, 40
25
26
27
28
29
30
31
32–39
EP
NAME
MUX0
CLKI+
CLKI-
DIN+
DIN-
LOADI
I.C.
R0–R7
G0–G7
V
DD
LOADO
DOUT-
DOUT+
CLKO-
CLKO+
MUX1
AGND
B7–B0
GND
FUNCTION
Multiplex 0 Active-Low, Open-Drain Output. Use
MUX0
to drive a pnp transistor.
PWM and Serial-Interface Noninverting Clock LVDS Input
PWM and Serial-Interface Inverting Clock LVDS Input
Serial-Interface Noninverting Data LVDS Input
Serial-Interface Inverting Data LVDS Input
Serial-Interface Load CMOS Input
Internally Connected. Connect to GND.
Red LED Drive Outputs. R0 to R7 are open-drain, constant-current sinks.
Green LED Drive Outputs. G0–G7 are open-drain, constant-current sinks.
Positive Supply Voltage. Bypass V
DD
to GND with a 0.1µF ceramic capacitor.
Serial-Interface Load CMOS Output
Serial-Interface Inverting Data LVDS Output
Serial-Interface Noninverting Data LVDS Output
PWM and Serial-Interface Inverting Clock LVDS Output
PWM and Serial-Interface Noninverting Clock LVDS Output
Multiplex 1 Active-Low, Open-Drain Output. Use
MUX1
to drive a pnp transistor.
Analog Ground. Connect to GND.
Blue LED Drive Outputs. B0 to B7 are open-drain, constant-current sinks.
Power Ground. Exposed pad on package underside must be connected to GND.
MAX6974/MAX6975
_______________________________________________________________________________________
5
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