MAX6974EVKIT Ver la hoja de datos (PDF) - Maxim Integrated
Número de pieza
componentes Descripción
Fabricante
MAX6974EVKIT Datasheet PDF : 16 Pages
| |||
MAX6974 Evaluation Kit
Slideshow Demo
The EV kit software can load a sequence of test pat-
terns. From the Command menu, select Slideshow,
then choose a folder containing test pattern files (see
Figure 4). The time between patterns can be adjusted
between 50ms and 30s.
Detailed Description of Hardware
The MAX6974 precision current-sinking, 24-output PWM
LED drivers (U1, U2) drive a 4 x 8 multiplexed grid of
red-green-blue LEDs in the common-anode configura-
tion. Common-emitter pnp BJTs (Q1–Q4) switch the
LED supply voltage in the multiplexing configuration.
See Tables 1 and 2.
Table 1. LED Nonmultiplexing
IC/PORT
U1 port R
U1 port G
U2 port R
U2 port G
U1 port B
U2 port B
LED DEVICES DRIVEN
D1 to D8
D1 to D8
D9 to D16
D9 to D16
D1 to D8
D9 to D16
COLORS
Red
Green
Red
Green
Blue
Blue
Table 2. LED Multiplexing
IC/PORT
U1 port R
U1 port G
U2 port R
U2 port G
U1 port B
U2 port B
LED DEVICES DRIVEN
D1 to D8
D17 to D24
D1 to D8
D17 to D24
D9 to D16
D25 to D32
D9 to D16
D25 to D32
D1 to D8
D9 to D16
D17 to D24
D25 to D32
COLORS
Red
Green
Red
Green
Blue
Blue
User-supplied DC power between 5V and 7V, applied
between the VLED and GND pads, is regulated by three
MAX1658/MAX1659 low-dropout linear regulators (U7,
U8, and U9) to produce 5V, 3.3V, and 2.5V supply rails.
The MAXQ2000 microcontroller (U3) drives the
MAX9112 LVDS level shifter (U4). When JU14–JU18 are
in the 1-2 position, this microcontroller drives the
MAX6974 LED display drivers (U1, U2). A 32MHz crys-
tal oscillator (Y2) is used to demonstrate optimum PWM
frequency by driving the LVDS clock signal between
command sequences. During command sequences,
the MAXQ2000 bit bangs the LVDS clock at 2.8MHz.
When used with the software, the MAX3311 (U6) trans-
lates the RS-232 signal levels from the COM port (P1) to
logic-level signals. Resistor-dividers R17/R18 convert
the 5V logic output into 3.3V logic.
When JU14–JU18 are in the 2-3 position, external LVDS
signals must be applied to connector J2. In this slave
configuration, the MAXQ2000 (U3), MAX9112 (U4), and
MAX3311 (U6) are not used.
LED Power Dissipation
Peak LED current is set by each port’s LED current cali-
bration register. This 8-bit DAC allows peak LED cur-
rent to be reduced to between 20% and 100% of the
full-scale rating, 30mA. Setting the current calibration
register to a value of 0 limits the peak LED current to
6mA (20% of 30mA). By writing different values to the
red, green, and blue ports’ current calibration registers,
the display’s color balance can be adjusted to compen-
sate for LED efficacy variations.
The evaluation kit is shipped from the factory with an
LED type (Stanley URGB1308B) that has a maximum rat-
ing of 20mA forward current or 84mW power dissipation.
Evaluating the MAX6975
The MAX6974 EV kit’s software and firmware are only
capable of driving 12-bit PWM values. If the EV kit were
used to drive the MAX6975s instead, then the two least
significant bits of the individual pixel PWM values are
not accessible. See Tables 3 and 4.
Table 3. Device Comparison—
Nonmultiplexed Operation
MAX6974 MAX6975
OPERATION
7 bits
5 bits Global-intensity control PWM resolution
3 (R, G, B)
3 (R, G, B)
Number of LED current calibration
registers
8 bits
8 bits LED current calibration resolution
30mA
30mA
Maximum LED drive current
(LED current calibration = 255)
6mA
6mA
LED drive current
(LED current calibration = 0)
24
12 bits
24
14 bits
Number of pixels
Individual pixel PWM-intensity-control
resolution
4 _______________________________________________________________________________________
Share Link: 