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MAX6972

16-Output PWM LED Drivers for Message Boards

Maxim Integrated 

16-Output PWM LED Drivers

for Message Boards

LED Intensity Control

The MAX6972/MAX6973 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 MAX6972/MAX6973 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 DACs

The 8-bit Y and Z CALDACs set the output current level

for all 8 outputs in the Y and Z ports, respectively (see

the MAX6972/MAX6973 Block Diagrams). The Y

CALDAC and Z CALDAC range from a low of 11mA

(0x00) to a maximum of 55mA (0xFF), providing

172µA/step of current trimming. The CALDACs are

loaded by the serial interface using command 01 (see

Table 4). The Z CALDAC data is loaded first, followed

by the Y CALDAC data (see the Serial Interface section).

The loaded data takes effect immediately.

Global-Intensity Control

The MAX6972/MAX6973 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 MAX6972/

MAX6973 at fCLKI = 31.5MHz allows a video-frame

update rate of 60fps for full-motion video (see the

MAX6972 Video-Frame Timing and MAX6973 Video-

Frame Timing sections).

The MAX6972/MAX6973 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 MAX6972 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 MAX6973 features 5-, 4-, 3-, and 2-bit

global-intensity control to yield 32, 16, 8, and 4 sub-

frames per frame, respectively.

The MAX6972/MAX6973 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.

(mA)

100%

50

40

50%

30

CALDAC

CURRENT

55mA MAX

GLOBAL-INTENSITY

PDM

INDIVIDUAL-INTENSITY

PWM

40mA 100%

100%

20

0%

10 11mA MIN

0

50%

CALDAC

= 169

0%

255 0

50%

0%

GLOBAL 127 0

= 96

Yn or Zn IAVE = 18.750mA

Yn or Zn PWM 4095

= 2560

Figure 2. Relationship Among the CALDACs, Global-Intensity, and Individual-Intensity PWM Controls

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