MAX6975ATL+ ,24-Output PWM LED Drivers for Message BoardsApplicationsB1 38 13 R5LED Video Display Panels+39 12 R4B0LED Message Boards40 11 R3VDDVariable Mes ..
MAX697CPE ,Microprocessor Supervisory CircuitsELECTRICAL CHARACTERISTICS
(Vcc = full operating range, VBATT = 2.8V, TA 2 25°C, unless otherwis ..
MAX697CWE ,Microprocessor Supervisory CircuitsGeneral Description
The MAX696/697 supervisory circuits reduce the
complexity and number of com ..
MAX697CWE+ ,Microprocessor Supervisory CircuitsApplicationsMAX69613 LLIN4● Computers GND● Controllers12 N.C.BATT ON 5● Intelligent Instruments● Cr ..
MAX697CWE+T ,Microprocessor Supervisory CircuitsFeatures● Adjustable Low-Line Monitor and Power-Down ResetThe MAX696/MAX697 supervisory circuits re ..
MAX697EWE ,Microprocessor Supervisory CircuitsELECTRICAL CHARACTERISTICS
(Vcc = full operating range, VBATT = 2.8V, TA 2 25°C, unless otherwis ..
MB401 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts
MB401 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts
MB401 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts
MB40166 ,AD/DA CONVERTERFUJITSU SEMICONDUCTORDS04-28500-5EDATA SHEETASSPAD/DA CONVERTERMB40166/MB401761-CHANNEL 6-BIT AD/DA ..
MB40176 ,AD/DA CONVERTERFUJITSU SEMICONDUCTORDS04-28500-5EDATA SHEETASSPAD/DA CONVERTERMB40166/MB401761-CHANNEL 6-BIT AD/DA ..
MB40176 ,AD/DA CONVERTERFUJITSU SEMICONDUCTORDS04-28500-5EDATA SHEETASSPAD/DA CONVERTERMB40166/MB401761-CHANNEL 6-BIT AD/DA ..
MAX6974ATL+-MAX6975ATL+
24-Output PWM LED Drivers for Message Boards
General DescriptionThe 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 MUX0and 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.
ApplicationsLED Video Display Panels
LED Message Boards
Variable Message Signs (VMS)
Signs
Graphic Panels
Features24 LED Current Sink Outputs (Three Banks of
Eight Outputs)48 LED Drive Option When Multiplexing33MHz Clock Supports Up to 63 Frames per
Second of VideoConstant Output Current Calibration from 6mA to30mA in 256 StepsEZCascade™Interface Simplifies Multiple Driver
Cascading Without External Buffers12-Bit or 14-Bit Individual PWM LED Intensity
Controls7-Bit or 5-Bit Panel PWM-Intensity Control+3V to +7V LED Power Supply+3.0V to +3.6V Logic SupplyOpen-Circuit LED Fault DetectionOptional Watchdog Timer Blanks Display if
Interface FailsStandard -40°C to +125°C Operating Temperature
Range
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards19-0555; Rev 2; 10/07
EVALUATION KIT
AVAILABLE*EP = Exposed paddle.
+Denotes a lead-free package.
MAX6974ATL/
MAX6975ATL
TQFN-EPTOP VIEW
6728
EP*3026242322B2R6
VDDB7G410
AGNDR1R0
I.C.
LOADI
DIN-
DIN+
CLKI-
CLKI+MUX0
CLKO+CLK0-DOUT+DOUT-LOADOVG6G5MUX1
Pin Configuration
Ordering Information
PARTTEMP RANGEPIN-
PACKAGE
PKG
CODE
MAX6974ATL+-40°C to +125°C40 TQFN-EP*T4066-3
MAX6975ATL+-40°C to +125°C40 TQFN-EP*T4066-3
EZCascade is a trademark of Maxim Integrated Products, Inc.
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards
ABSOLUTE MAXIMUM RATINGSStresses 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.
(All voltages with respect to GND.)
VDD........................................................................-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 (VDD+ 0.3V)
Continuous Power Dissipation (TA= +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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Supply VoltageVDD3.03.6V
LEDs Anode Voltage
(R0–R7, G0–G7, B0–B7, MUX0,
and MUX1)7V
fCLKI = 0Hz; CLKO_, DOUT_ loaded 200Ω;
calibration DACs set to 0x012852
fCLKI = 0Hz; CLKO_, DOUT_ loaded 200Ω;
calibration DACs set to 0xFF5172Supply CurrentIDD
fCLKI = 32MHz; CLKO_, DOUT_ loaded 200Ω;
calibration DACs set to 0xFF5477
Input High Voltage LOADIVIHC0.7
x VDDV
Input Low Voltage LOADIVILC0.3
x VDDV
Differential Input Voltage Range
CLKI_, DIN_VID±0.15±1.20V
Common-Mode Input Voltage
CLKI_, DIN_VCM| V I D / 2| 2.4V
Differential Input High ThresholdVDIFFTH8100mV
Differential Input Low ThresholdVDIFFTL-100-8mV
Differential Output Voltage
CLKO_, DOUT_VODTermination 200Ω at receiver _+ and _- inputs±190±550mV
Differential Output Offset
CLKO_, DOUT_VOSTermination 200Ω at receiver _+ and _- inputs1.1251.251.375V
Input Leakage Current
CLKI_, DIN_, LOADIIIH, IIL-1+1µA
Input Capacitance
CLKI_, DIN_, LOADI10pF
Output Low Voltage LOADOVOLCISINK = 5mA0.050.25V
Output High Voltage LOADOVOHCISOURCE = 5mAVDD
- 0.5
VDD
- 0.2V
ELECTRICAL CHARACTERISTICS(VDD= 3.0V to 3.6V, TA= TMINto TMAX, unless otherwise noted. Typical values are at VDD= 3.3V, TA= +85°C.) (Note 1)
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards
Note 1:All parameters tested at TA= +85°C. Specifications over temperature are guaranteed by design.
Note 2: Specification limits apply to devices at the same TAfor TA= TMINto TMAX.
Note 3:Guaranteed by design.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOutput Slew Time LOADO20% to 80%, 80% to 20%, load = 10pF3ns
Output Low Voltage MUX_VOLMISINK = 40mA0.4V
Open-Circuit DetectionVOCD200mV
Output Voltage Slew Time
R0–R7, G0–G7, B0–B7
80% to 20%, load = 50pF,
calibration DACs set to 0xFF100ns
TA = +85°C29.43030.6
TA = +125°C29.1030.90Full-Scale Port Output Current
R0–R7, G0–G7, B0–B7ISINKFSVDD = 3.3V, VO = 1.2V,
calibration DACs set to 0xFF
TA = TMIN to TMAX28.231.8
TA = +125°C
(Note 3)0.51.7
TA = +85°C0.31Port-to-Port Current Matching
R0–R7, G0–G7, B0–B7ΔISINK
VDD = 3.3V, VO = 1.2V,
calibration DACs set to 0xFF
ISINK = 30mA (Note 2)TA = -40°C
(Note 3)±0.93.0
TA = +85°C0.31.15
Output Load RegulationΔIOLRD D = 3.3V , V O = 1.2V to 3.0V ,
calibration DACs set to 0x80,
ISINK = 18mATA = TMIN to TMAX1.5
mA/V
TA = +85°C0.61.7
Output Power-Supply RejectionΔIOPSRD D = 3.0V to 3.6V , V O = 1.2V ,
calibration DACs set to 0x80,
ISINK = 18mATA = TMIN to TMAX2.0
mA/V
ELECTRICAL CHARACTERISTICS (continued)(VDD= 3.0V to 3.6V, TA= TMINto TMAX, unless otherwise noted. Typical values are at VDD= 3.3V, TA= +85°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSCLKI_ Input FrequencyfCLKI33MHz
CLKI_ Duty Cycle4060%
CLKO_ Output DelaytPD-CLKO19ns
DIN_ Setup TimetSU-DIN0.5ns
DIN_ Hold TimetHD-DIN5ns
DOUT_ Output DelaytPD-DOUT18ns
LOADO Output DelaytPD-LOADO21ns
LOADI Hold TimetHD-LOADI11ns
Watchdog PeriodWhen enabled40125300ms
TIMING CHARACTERISTICS(VDD= 3.0V to 3.6V, TA= TMINto TMAX, unless otherwise noted. Typical values are at 3.3V, TA= +85°C.) (Note 1)
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards
Typical Operating Characteristics(VDD= 3.3V, TA= +25°C, unless otherwise noted.)
OPERATING CURRENT CONSUMPTION
vs. SUPPLY VOLTAGE VDDMAX6974 toc01
SUPPLY VOLTAGE VDD (V)
IDD
(mA)
TA = -40°CTA = +25°C
TA = +125°C
TA = +85°C
fCLKI = 32MHz
CALDAC = 0xFF
OPERATING CURRENT CONSUMPTION
vs. SUPPLY VOLTAGE VDDMAX6974 toc02
SUPPLY VOLTAGE VDD (V)
IDD
(mA)
TA = -40°CTA = +25°C
TA = +85°CTA = +125°C
fCLKI = 0MHz
CALDAC = 0x00
LED OUTPUT SINK CURRENT
vs. OUTPUT VOLTAGEMAX6974 toc03
OUTPUT VOLTAGE (V)
ISINK
(mA)4321
TA = -40°C
TA = +125°C
TA = +25°C
TA = +85°C
LED OUTPUT SINK CURRENT
vs. OUTPUT VOLTAGEMAX6974 toc04
OUTPUT VOLTAGE (V)
ISINK
(mA)4321
VDD = +3.0V
VDD = +3.3VVDD = +3.6V
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards
Pin Description
PINNAMEFUNCTIONMUX0Multiplex 0 Active-Low, Open-Drain Output. Use MUX0 to drive a pnp transistor.CLKI+PWM and Serial-Interface Noninverting Clock LVDS InputCLKI-PWM and Serial-Interface Inverting Clock LVDS InputDIN+Serial-Interface Noninverting Data LVDS InputDIN-Serial-Interface Inverting Data LVDS InputLOADISerial-Interface Load CMOS InputI.C.Internally Connected. Connect to GND.
8–15R0–R7Red LED Drive Outputs. R0 to R7 are open-drain, constant-current sinks.
16–23G0–G7Green LED Drive Outputs. G0–G7 are open-drain, constant-current sinks.
24, 40VDDPositive Supply Voltage. Bypass VDD to GND with a 0.1µF ceramic capacitor.LOADOSerial-Interface Load CMOS OutputDOUT-Serial-Interface Inverting Data LVDS OutputDOUT+Serial-Interface Noninverting Data LVDS OutputCLKO-PWM and Serial-Interface Inverting Clock LVDS OutputCLKO+PWM and Serial-Interface Noninverting Clock LVDS OutputMUX1Multiplex 1 Active-Low, Open-Drain Output. Use MUX1 to drive a pnp transistor.AGNDAnalog Ground. Connect to GND.
32–39B7–B0Blue LED Drive Outputs. B0 to B7 are open-drain, constant-current sinks.GNDPower Ground. Exposed pad on package underside must be connected to GND.
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards
MAX6974 Block DiagramR LED DRIVERS
R7–R0ISET
ISET8-BIT
G CALDAC
MUX1
OUTPUTS
7-BIT GLOBAL-INTENSITY PDM MODULATOR
12-BIT INDIVIDUAL PWM MODULATOR8
CALIBRATION
DATA LATCH
GLOBAL-
INTENSITY
DATA LATCH8
MUX0 PIXEL PWM NEW DATA LATCHMUX1 PIXEL PWM NEW DATA LATCH
EXT. PNPEXT. PNPEN
PWM
COUNTERS
SYNC
288-BIT DATA SHIFT REGISTER
CLKI
LOADI
CLKO
DOUTDIN
CONTROL
MUX0 PIXEL PWM OLD DATA LATCHLOAD
MUX1 PIXEL PWM OLD DATA LATCHOE
LOAD
MUX0
OUTPUT
24-BIT NEW HEADER
SHIFT REGISTERSYNC DETECTR5R4R3R2R1R0
8-BIT
R CALDAC
R LED OUTPUTS
G LED DRIVERS
G7–G0G6G5G4G3G2G1G0
G LED OUTPUTS
LOADO
ISET8-BIT
B CALDAC
B LED DRIVERS
B7–B0B6B5B4B3B2B1B0
B LED OUTPUTS
0/1
MAX6974
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards
MAX6975 Block DiagramR LED DRIVERS
R7–R0ISET
ISET8-BIT
G CALDAC
MUX1
OUTPUTS
5-BIT GLOBAL-INTENSITY PDM MODULATOR
14-BIT INDIVIDUAL PWM MODULATOR8
CALIBRATION
DATA LATCH
GLOBAL-
INTENSITY
DATA LATCH8
MUX0 PIXEL PWM NEW DATA LATCHMUX1 PIXEL PWM NEW DATA LATCH
EXT. PNPEXT. PNPEN
PWM
COUNTERS
SYNC
336-BIT DATA SHIFT REGISTER
CLKI
LOADI
CLKO
DOUTDIN
CONTROL
MUX0 PIXEL PWM OLD DATA LATCHLOAD
MUX1 PIXEL PWM OLD DATA LATCHOE
LOAD
MUX0
OUTPUT
24-BIT NEW HEADER
SHIFT REGISTERSYNC DETECTR5R4R3R2R1R0
8-BIT
R CALDAC
R LED OUTPUTS
G LED DRIVERS
G7–G0G6G5G4G3G2G1G0
G LED OUTPUTS
LOADO
ISET8-BIT
B CALDAC
B LED DRIVERS
B7–B0B6B5B4B3B2B1B0
B LED OUTPUTS
0/1
MAX6975
MAX6974/MAX6975
Detailed DescriptionThe MAX6974/MAX6975 drive 24 nonmultiplexed LEDs
or 48 multiplexed LEDs for various indoor and outdoor
display applications. The EZCascade serial interface
enables large multidriver display panels to be con-
structed with interconnected MAX6974/MAX6975
devices (see Figure 1).
The drivers provide 12-bit (MAX6974) or 14-bit
(MAX6975) individual PWM steps for each LED output.
Four to seven global-intensity bits provide additional
pulse-density modulation (PDM) intensity control (see
Table 1). The MAX6974/MAX6975 provide 19 bits of
total current/intensity control range per color per pixel,
or 18 bits if multiplexing. The total PWM dynamic range
encompasses gamma correction and, if desired, indi-
vidual LED calibration.
LED outputs are grouped in ports (R, G, and B) with
eight LED outputs per port. Each port features its own
current calibration control DAC (CALDAC) with 0.31%
resolution to set the current. The MAX6974/
MAX6975 current calibration feature allows unmatched
LEDS from different lots and manufacturers to be
color matched.
Power-UpOn power-up, the MAX6974/MAX6975 set the calibration
current to the minimum current for all LED outputs and
clear the global-intensity PDM data, individual-intensity
PWM data, and the timing counters. The display
remains blank after CLKI starts running. The watchdog
function is inactive after power-up.
24-Output PWM LED Drivers
for Message BoardsHOST
CLKO
DOUT
LOADO
CLKI
DIN
LOADI
MAX6974/
MAX6975
MAX6974/
MAX6975
MAX6974/
MAX6975
MAX6974/
MAX6975
CLKI
DIN
LOADI
CLKO
DOUT
LOADO
CLKI
DIN
LOADI
CLKO
DOUT
LOADO
CLKI
DIN
LOADI
CLKO
DOUT
LOADO
CLKI
DIN
LOADI
CLKO
DOUT
LOADO
OPTIONAL FEEDBACK
Figure 1. Generic Cascaded Connection Scheme
GLOBAL PDMPARTLED DRIVE
OUTPUTS
LED DRIVE
CURRENT
CALIBRATION
DAC RANGEDIRECTMULTIPLEXED
INDIVIDUAL
PWM
MAX69747 bits6 bits12 bits
5 bits4 bits
MAX6975(7V rated)30mA6mA to 30mA
3 bits2 bits14 bits
Table 1. Comparison of MAX6974/MAX6975
LED-Intensity ControlThe MAX6974/MAX6975 provide three levels of output
current control for LED drive: calibration DACs
(CALDACs), global-intensity control, and individual-
intensity control. The CALDACs set the port output cur-
rent levels, while the global-intensity and individual-
intensity controls modulate the output current on/off
times, providing a fine-resolution control of average
output currents (see Figure 2). The individual-intensity
control operates on each output independently to set
each individual LED intensity level. The global-intensity
controls modulate MAX6974/MAX6975 outputs simulta-
neously for a uniform brightness control without affect-
ing color. Using a fixed output current level that is
modulated only by on/off control leaves the LED color
unaffected while precisely controlling intensity. Finally,
all outputs can be turned on and off simultaneously by
setting or clearing configuration bit D3 (PWM-ON).
Calibration DACsThe 8-bit R, G, and B CALDACs set the output current
level for all eight outputs in the R, G, and B ports,
respectively (see the MAX6974 Block Diagram and
MAX6975 Block Diagram). The R CALDAC, G
CALDAC, and B CALDAC range from a low of 6mA
(0x00) to a maximum of 30mA (0xFF), providing
94µA/step of current trimming. The CALDACs are
loaded by the serial interface using command 01 (see
Table 4). The B CALDAC data is loaded first, followed
by the G CALDAC data, and then the R CALDAC data
(see the Serial Interfacesection).The loaded data takes
effect immediately.
Global-Intensity ControlThe MAX6974/MAX6975 adjust global and individual
intensities over a time period called a frame. One frame
requires 219(524,288) periods of CLKI and corre-
sponds to one video-frame time. Video frames generally
contain consecutive images displayed rapidly to yield
a motion picture display. Running the MAX6974/
MAX6975 at fCLKI= 31.5MHz allows a video-frame
update rate of 60fps for full-motion video (see the
MAX6974 Video-Frame Timingand MAX6975 Video-
Frame Timingsections).
The MAX6974/MAX6975 further divide frames into sub-
frames to allow a unique combination of global- and
individual-intensity controls. The number of subframes
is equal to the number of global-intensity control steps.
The MAX6974 uses 128 subframes per frame in
nonmultiplexed mode (corresponding to 7-bit global-
intensity PDM control) and 64 subframes in multiplexed
mode (corresponding to 6-bit global-intensity PDM
control). The MAX6975 features 5-, 4-, 3-, and 2-bit
global-intensity control to yield 32,16, 8, and 4 sub-
framesper frame, respectively.
The MAX6974/MAX6975 control global intensity by
driving subframes on and off. When a subframe is on, it
allows the individual PWM intensity control to be driven
on the outputs. Subframes that are off do not have any
PWM modulation on the outputs.
Individual PWM ControlThe MAX6974/MAX6975 further modulate the time that
each subframe is ON by a pulse-width modulation
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards(mA)CALDAC
CURRENT
30mA MAX
6mA MIN
1270GLOBAL
= 96
GLOBAL-INTENSITY
PDM
INDIVIDUAL-INTENSITY
PWM
40950Rn, Gn, OR Bn PWM
= 2560
Rn, Gn, OR Bn IAVE = 10.22mA
CALDAC
= 169
21.8mA
100%
50%
100%
50%
100%
50%
Figure 2. Relationship Among the CALDACs, Global-Intensity, and Individual-Intensity PWM Controls
MAX6974/MAX6975(PWM) value. Each output current driver in the R, G,
and B ports has a unique 12-bit (MAX6974) or 14-bit
(MAX6975) PWM control value providing fine resolution
adjustment of average current output. Each bit time of
the PWM corresponds to one period of CLKI (TCLKI).
The PWM setting determines the amount of time, out of
the total period, that the output is on. The subframes
have PWM off-zones at the start (tSPWM) and end
(tEPWM) of the PWM period (see Figure 3). The sub-
frame period and PWM off zones are shown in Table 2
for each device.
The MAX6974 subdivides each subframe by 4096
(12-bit) PWM steps and has 16 cycle off zones, leaving
an active PWM region of 4064 PWM steps ranging from
16 to 4079. The MAX6975 subdivides each subframe
by 16,384 (14-bit) PWM steps and has 32 cycle off
zones, leaving an active PWM region of 16,320 PWM
steps ranging from 32 to 16,351. The PWM phase for
outputs R0, R2, R4, R6, G0, G2, G4, G6, B0, B2, B4,
and B6 use phasing with the outputs on first and off
second. Inverse phasing is used for outputs R1, R3,
R5, R7, G1, G3, G5, G7, B1, B3, B5, and B7 as shown
in Figure 3 to balance the timing of loads on the LED
anode power supply.
In multiplexed operation, the subframes are shared
between MUX0and MUX1active times, effectively
reducing the number of subframes by 2.
LED-Intensity Control ExampleThe three levels of intensity control are shown in Figure 2
for one LED output driver in a MAX6974 in nonmulti-
plexed mode. As an example, the CALDAC is set to
169DEC,setting the port output current level to 21.8mA.
The global-intensity PDM value is set to 96DEC, producing
an even distribution of ON subframes out of the 128
24-Output PWM LED Drivers
for Message BoardsR0, R2, R4, R6
G0, G2, G4, G6
B0, B2, B4, B6
R1, R3, R5, R7
G1, G3, G5, G7
B1, B3, B5, B7
R0, R2, R4, R6
G0, G2, G4, G6
B0, B2, B4, B6
R1, R3, R5, R7
G1, G3, G5, G7
B1, B3, B5, B7
SUBFRAME (n)SUBFRAME (n + 1)
tSPWM
tEMUX
tEMUX
MUX0
SUBFRAME (n), MUX0SUBFRAME (n), MUX1
MUX1
tSPWM
tSPWMtEPWM
MULTIPLEXED
NONMULTIPLEXED
tSPWMtEPWM
ON/OFF PHASING
OFF/ON PHASING
ON/OFF PHASING
OFF/ON PHASING
50%75%
100%25%
75%75%
75%75%
PARTSUBFRAME
(TCLKI)
tSPWM
(TCLKI)
tEPWM
(TCLKI)
tEMUX
(TCLKI)
MAX69744096161616
MAX697516,384323232
Table 2. Subframe and PWM Timing
possible (shown in Figure 4 as subframes 1, 3, 4, 5, etc).
Each subframe can be ON for a PWM duration set by the
individual PWM value. The PWM value setting of
2560DECout of 4096 (12-bit) results in a further reduction
of current ON time (shown in bold trace).
The internal PDM logic spreads the on subframes as
evenly as possible among the off subframes to keep
the effective scanning frequency high.
For applications with a slower clock speed, the
MAX6975 can increase the display refresh rate by a
factor of four to eliminate visible flicker. Setting configu-
ration bit D4 (GLB4) to 1 activates the increased
refresh rate (see Table 6). The increased refresh rate
reduces the number of global-intensity settings by a
factor of four (see Table 3).
MAX6974 Video-Frame TimingThe MAX6974 supports up to 60 video frames per
second (fps). The following equation shows the
required clock frequency to support 60 video fps:
60 (video fps) x 4096 (clocks per 12-bit PWM period) x
128 (global-intensity subframes) = 31.5MHz.
The MAX6974 supports up to a 33MHz clock signal
(~63fps).
Each 12-bit PWM period contains 4096 clock cycles;
multiply that number by 128 (number of global-intensity
subframes) to obtain the required number of clock cycles
(524,288) per video frame. The MAX6974 requires 36
bits (12 bits per color multiplied by three colors) to drive
an RGB pixel. The maximum pixel data that the
MAX6974 can send per video frame is 524,288 / 36 or
14,563 pixels,corresponding to 1820 cascaded
MAX6974s.
MAX6975 Video-Frame TimingThe MAX6975 also supports up to 60 video frames per
second (fps). The following equation shows the
required clock frequency to support 60 video fps:
60 (video fps) x 16,384 (clocks per 14-bit PWM period)
x 32 (global-intensity subframes) = 31.5MHz.
The MAX6975 supports up to a 33MHz clock signal
(~63fps).
Each 14-bit PWM period contains 16,384 clock cycles;
multiply 16,384 by 32 (global-intensity subframes) to
obtain the required number of clock cycles (524,288)
per video frame. The MAX6975 requires 42 bits (14 bits
per color multiplied by three colors) to drive an RGB
pixel. The maximum pixel data that the MAX6975 can
send per video frame is 524,288 / 42 or 12,483 pixels,
corresponding to 1560 cascaded MAX6975s.
Multiplexed vs. Nonmultiplexed OperationThe MAX6974/MAX6975 can double the number of
LEDs driven from 24 to 48 through multiplexing. When
multiplexing, the two outputs, MUX0and MUX1, drive
MAX6974/MAX6975
24-Output PWM LED Drivers
for Message Boards169d = 20
SUBFRAME NUMBER
30mA MAX
6mA MIN
(mA)234567891011
CALDAC CURRENT
OUTPUT LED CURRENTPWM = 2560/4096
ONE FRAME IS 219 (524,288) CLKI CYCLES LONG
GLOBAL PDM = 96/128 SUBFRAMESONONONONONONON
Figure 4. The three levels of LED current control (CALDAC, global-intensity PDM, and individual PWM) modulate the average output
MAX6974/MAX6975two external pnp transistors, such as FMMTL717, used
as common-anode power switches (see Figure 5).
Setting configuration bit D0 to 1 enables multiplex
operation. MUX0and MUX1alternate the LED anode
drive voltage between two sets of LEDs. The R, G, and
B ports provide individual PWM control during alternate
24-Output PWM LED Drivers
for Message BoardsR1R2R3R4R5R6R7
(REDS)
(REDS)
(GREENS)
(GREENS)
(BLUES)
(BLUES)
FMMTL717
120pF
+5.55V
FMMTL717
560180120pFG2G3G4G5G6G7G0B2B3B4B5B6B7B0
MUX0
MUX1
SUBFRAME 15
MUX1
16,384 CLKs
SUBFRAME 0
MUX0
16,384 CLKs
SUBFRAME 0
MUX1
16,384 CLKs
SUBFRAME 1
MUX0
16,384 CLKs
SUBFRAME 1
MUX1
16,384 CLKs
SUBFRAME 14
MUX0
16,384 CLKs
SUBFRAME 14
MUX1
16,384 CLKs
SUBFRAME 15
MUX0
16,384 CLKs
SUBFRAME 15
MUX1
16,384 CLKs
SUBFRAME 0
MUX0
16,384 CLKs
ONE COMPLETE 524,288 CLOCK CYCLE MUL
TIPLEXED VIDEO FRAME
