MAX6973 Ver la hoja de datos (PDF) - Maxim Integrated
Número de pieza
componentes Descripción
Fabricante
MAX6973 Datasheet PDF : 23 Pages
| |||
16-Output PWM LED Drivers
for Message Boards
Table 3. MAX6972/MAX6973 Timing Comparison
PART
MAX6972
MAX6973
MUX
BIT
0
1
0
1
OPERATION
Nonmultiplex
Multiplex
Nonmultiplex
Multiplex
PWM
RES.
12 bits
14 bits
TOTAL CLOCKS PER USEABLE CLOCKS PER
PWM SUBFRAME
PWM SUBFRAME
4096
4064
MAXIMUM PWM
DUTY CYCLE
4064 / 4096 = 99.22%
16,384
16,320
16,320 / 16,384 = 99.61%
PART GLB4
BIT
X
MAX6972
X
0
MAX6973
1
MUX
BIT
0
1
0
1
0
1
OPERATION
Nonmultiplex
Multiplex
Nonmultiplex
Multiplex
Nonmultiplex
Multiplex
GLOBAL
PDM
RES.
7 bits
6 bits
5 bits
4 bits
3 bits
2 bits
SUBFRAMES
PER FRAME
128
64
32
16
8
4
CLOCKS
PER
FRAME
524,288
524,288
131,072
CLOCK
CLOCK
FREQUENCY (MHz) FREQUENCY (MHz)
FOR 50fps
FOR 60fps
26.2144
31.45728
26.2144
31.45728
6.5536
7.8643
Setting configuration bit D0 to 1 enables multiplex
operation. MUX0 and MUX1 alternate the LED anode
drive voltage between two sets of LEDs. The Y and Z
ports provide individual PWM control during alternate
MUX cycles as shown in Figure 3. The alternating MUX
cycles reduce the global-intensity resolution (the num-
ber of subframes) by half, which reduces the average
LED current by half.
Watchdog
A selectable watchdog timer monitors serial-interface
inputs CLKI, DIN, and LOADI. Enabling the watchdog
timer requires that CLKI, DIN, and LOADI toggle at
least once every 40ms. If any of these transitions fails to
occur, then the individual-intensity PWM data latches
clear. This condition effectively blanks the LEDs.
Update the individual-intensity PWM data registers to
turn the LEDs back on. The watchdog timeout does not
affect the calibration or global-intensity data, the clock
synchronization, or multiplexed/nonmultiplexed setting.
Use the watchdog functionality in safety-critical appli-
cations where a blanked display is safer than an incor-
rect display.
LED Open-Circuit and
Overtemperature Detection
The MAX6972/MAX6973 feature two fault detection func-
tions: open-circuit LED outputs and overtemperature. An
LED open-circuit is detected on driver outputs by moni-
toring for output voltages below 200mV. When an open
circuit is detected, the MAX6972/MAX6973 increments
a fault counter included in the serial-interface protocol
that can be routed back to the host transmitter for diag-
nostics. Any number of open-circuit LEDS, multiplexed
or nonmultiplexed, can be detected, however only one
counter increment occurs per device.
The MAX6972/MAX6973 detect die temperatures
above TDIE = +165°C and disable all output drivers by
setting all PWM data to zero. The fault counter in the
serial-interface protocol is incremented by one count
for each cascaded device with an overtemperature
condition. The output drivers are turned back on when
the die temperature falls below TDIE = +150°C. The
fault counter value is distinguished between LED open-
circuit and overtemperature conditions by the serial-
interface command used at the time of detection (see
the Serial Interface section for more details).
______________________________________________________________________________________ 13
Share Link: 