Rainbow Electronics MAX6964 - Manual (Page 14)

MAX6964
17-Output LED Driver/GPO
with Intensity Control
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PWM Intensity Control
The MAX6964 includes an internal oscillator, nominally
32kHz, to generate PWM timing for LED intensity control
or other applications such as PWM trim DACs. PWM can
be disabled entirely for all the outputs. In this case, all
outputs are static and the MAX6964 operating current is
lowest because the internal PWM oscillator is turned off.
The MAX6964 can be configured to provide any combi-
nation of PWM outputs and glitch-free logic outputs.
Each PWM output has an individual 4-bit intensity con-
trol (
Table 12 ). When all outputs are to be used with the
same PWM setting, the outputs can be controlled
together instead using the global intensity control
(
Table 11 ). Table 8 shows how to set up the MAX6964
to suit a particular application.
PWM Timing
The PWM control uses a 240-step PWM period, divided
into 15 master intensity timeslots. Each master intensity
timeslot is divided further into 16 PWM cycles (
Figure 12 ).
The master intensity operates as a gate, allowing the indi-
vidual output settings to be enabled from 1 to 15 timeslots
per PWM period (Figures 13, 14, and 15) (
Table 11 ).
Each output’s individual 4-bit intensity control only
operates during the number of timeslots gated by the
master intensity. The individual controls provide 16
intensity settings from 1/16 through 16/16 (
Table 12 ).
Figures 16, 17, and 18 show examples of individual
intensity control settings. The highest value an individ-
ual or global setting can be set to is 16/16. This setting
forces the output to ignore the master control, and fol-
low the logic level set by the appropriate blink phase
register bit. The output becomes a glitch-free static out-
put with no PWM.
Using PWM Intensity Controls with Blink Disabled
When blink is disabled ( Table 5 ), the blink phase 0 regis-
ters specify each output’s logic level during the PWM on-
time (
Table 6 ). The effect of setting an output’s blink
phase 0 register bit to zero or 1 is shown in Table 9 . With
its output bit set to zero, an LED can be controlled with 16
intensity settings from 1/16th duty through fully on, but
cannot be turned fully off using the PWM intensity control.
With its output bit set to 1, an LED can be controlled with
16 intensity settings from fully off through 15/16th duty.
Using PWM Intensity Controls with Blink Enabled
When blink is enabled ( Table 5 ), the blink phase 0 regis-
ters and blink phase 1 registers specify each output’s
logic level during the PWM on-time during the respective
blink phases (
Tables 6 and 7 ). The effect of setting an
output’s blink phase x register bit to 0 or 1 is shown in
Table 10. LEDs can be flipped between either directly on
and off, or between a variety of high/low PWM intensities.
Figure 12. PWM Timing
ONE PWM PERIOD IS 240 CYCLES OF THE 32kHz PWM
OSCILLATOR; A PWM PERIOD CONTAINS 15 MASTER
INTENSITY TIMESLOTS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 14 15 1 2
EACH MASTER INTENSITY
TIMESLOT CONTAINS 16
PWM CYCLES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 15 16 1 2
Figure 11. BLINK Logic
BLINK ENABLE FLAG E
BLINK FLIP FLAG B
BLINK INPUT
BLINK PHASE
REGISTERS