Rainbow Electronics MAX6964 - Manual (Page 15)

MAX6964
17-Output LED Driver/GPO
with Intensity Control
______________________________________________________________________________________ 15
Global/O16 Intensity Control
The 4 bits used for output O16’s PWM individual inten-
sity setting also double as the global intensity control
(
Table 11 ). Global intensity simplifies the PWM settings
when the application requires them all to be the same,
such as for backlight applications, by replacing the 17
individual settings with one setting. Global intensity is
enabled with the global intensity flag G in the configu-
ration register (
Table 4 ). When global PWM control is
used, the 4 bits of master intensity and 4 bits of global
intensity effectively combine to provide an 8-bit, 240-
step intensity control applying to all outputs.
It is not possible to apply global PWM control to a sub-
set of the ports, and use the others as logic outputs. To
mix static logic outputs and PWM outputs, individual
PWM control must be selected (
Table 8 ).
Applications Information
Output Level Translation
The open-drain output architecture allows the ports to
level translate the outputs to higher or lower voltages
than the MAX6964 supply. An external pullup resistor
can be used on any output to convert the high-imped-
ance logic-high condition to a positive voltage level.
The resistor can be connected to any voltage up to 7V.
For interfacing CMOS inputs, a pullup resistor value of
220kΩ is a good starting point. Use a lower resistance
to improve noise immunity, in applications where power
consumption is less critical, or where a faster rise time
is needed for a given capacitive load.
Driving LED Loads
When driving LEDs, a resistor in series with the LED
must be used to limit the LED current to no more than
50mA. Choose the resistor value according to the fol-
lowing formula:
R LED = (V SUPPLY - V LED - V OL ) / I LED
where:
R
LED
is the resistance of the resistor in series with the
LED (Ω).
V
SUPPLY is the supply voltage used to drive the LED (V).
V
LED
is the forward voltage of the LED (V).
V OL is the output low voltage of the MAX6964 when
sinking I LED (V).
I LED is the desired operating current of the LED (A).
For example, to operate a 2.2V red LED at 14mA from a
5V supply, R
LED = (5 - 2.2 - 0.25) / 0.014 = 182Ω.
Figure 15. Master Set to 15/15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 14 15 2 1
.
.
Figure 14. Master Set to 14/15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 14 15 2 1
.
.
Figure 13. Master Set to 1/15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 14 15 2 1
.
Figure 17. Individual (or Global) Set to 15/16
MASTER INTENSITY TIMESLOT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
NEXT MASTER INTENSITY TIMESLOT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Figure 16. Individual (or Global) Set to 1/16
MASTER INTENSITY TIMESLOT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
NEXT MASTER INTENSITY TIMESLOT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Figure 18. Individual (or Global) Set to 16/16
MASTER INTENSITY TIMESLOT CONTROL IS IGNORED
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16