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PDF MAX6974 Data sheet ( Hoja de datos )

Número de pieza MAX6974
Descripción (MAX6974 / MAX6975) 24-Output PWM LED Drivers
Fabricantes Maxim Integrated Products 
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19-0555; Rev 0; 5/06
24-Output PWM LED Drivers
for Message Boards
General Description
The MAX6974/MAX6975 precision current-sinking,
24-output PWM LED drivers drive red, green, and blue
LEDs for full-color graphic message boards and video
displays. Each output has an individual 12-bit (MAX6974)
or 14-bit (MAX6975) PWM-intensity (hue) control and
7-bit (MAX6974) or 5-bit (MAX6975) global PWM intensity
(luminance) control. The MAX6974/MAX6975 feature a
high-speed, fully buffered cascadable serial interface,
open-circuit LED fault detection circuitry, as well as a
watchdog timer.
The driver has three banks of eight outputs, with each
bank intended to drive a different color in RGB applica-
tions. The full-scale current for each bank of eight out-
puts is adjustable from 6mA to 30mA in 256 steps
(0.3125% per step) to calibrate each color.
The MAX6974/MAX6975 can optionally multiplex by
using outputs MUX0 and MUX1, which each drive an
external pnp transistor. Multiplexing doubles the
MAX6974/MAX6975 drive capability to 48 LEDs.
The MAX6974/MAX6975 operate from a 3.0V to 3.6V
power supply. The LED power supply can range from
3V to 7V. The LED drivers require only 0.8V headroom
above the LEDs’ forward-voltage drop. Using a sepa-
rate LED supply voltage for each LED minimizes power
consumption.
The serial interface uses differential signaling for the
high-speed clock and data signals to reduce EMI and
improve signal integrity. The MAX6974/MAX6975 buffer
all interface signals to simplify cascading devices in
modules that use a large number of drivers.
An internal watchdog timer, when enabled, automatically
clears the pixel-data registers and blanks the display if
any of the signal inputs fail to toggle within 40ms.
The MAX6974/MAX6975 are available in 40-pin TQFN
packages and operate over the -40°C to +125°C
temperature range.
Refer to the MAX6972/MAX6973 data sheet for a
16-output, 11mA to 55mA software-compatible device.
EZCascade is a trademark of Maxim Integrated Products, Inc.
Applications
LED Video Display Panels
LED Message Boards
Variable Message Signs (VMS)
Signs
Graphic Panels
Typical Operating Circuit appears at the end of data sheet.
Features
o 24 LED Current Sink Outputs (Three Banks of
Eight Outputs)
o 48 LED Drive Option When Multiplexing
o 33MHz Clock Supports Up to 63 Frames per
Second of Video
o Constant Output Current Calibration from 6mA to
30mA in 256 Steps
o EZCascade™ Interface Simplifies Multiple Driver
Cascading Without External Buffers
o 12-Bit or 14-Bit Individual PWM LED Intensity
Controls
o 7-Bit or 5-Bit Panel PWM-Intensity Control
o +3V to +7V LED Power Supply
o +3.0V to +3.6V Logic Supply
o Open-Circuit LED Fault Detection
o Optional Watchdog Timer Blanks Display if
Interface Fails
o Standard -40°C to +125°C Operating Temperature
Range
Ordering Information
PART
TEMP RANGE PIN-
PACKAGE
PKG
CODE
MAX6974ATL+ -40°C to +125°C 40 TQFN-EP* T4066-3
MAX6975ATL+ -40°C to +125°C 40 TQFN-EP* T4066-3
*EP = Exposed pad.
+Denotes lead-free package.
Pin Configuration
TOP VIEW
30 29 28 27 26 25 24 23 22 21
AGND 31
20 G4
B7 32
B6 33
19 G3
EP* 18 G2
B5 34
17 G1
B4 35
B3 36
B2 37
MAX6974ATL/
MAX6975ATL
16 G0
15 R7
14 R6
B1 38
B0 39
+
13 R5
12 R4
VDD 40
11 R3
1 2 3 4 5 6 7 8 9 10
*EP = EXPOSED PADDLE.
TQFN-EP
________________________________________________________________ Maxim Integrated Products 1
For pricing delivery, and ordering information please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

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MAX6974 pdf
PIN
1
2
3
4
5
6
7
8–15
16–23
24, 40
25
26
27
28
29
30
31
32–39
EP
NAME
MUX0
CLKI+
CLKI-
DIN+
DIN-
LOADI
I.C.
R0–R7
G0–G7
VDD
LOADO
DOUT-
DOUT+
CLKO-
CLKO+
MUX1
AGND
B7–B0
GND
24-Output PWM LED Drivers
for Message Boards
Pin Description
FUNCTION
Multiplex 0 Active-Low, Open-Drain Output. Use MUX0 to drive a pnp transistor.
PWM and Serial-Interface Noninverting Clock LVDS Input
PWM and Serial-Interface Inverting Clock LVDS Input
Serial-Interface Noninverting Data LVDS Input
Serial-Interface Inverting Data LVDS Input
Serial-Interface Load CMOS Input
Internally Connected. Connect to GND.
Red LED Drive Outputs. R0 to R7 are open-drain, constant-current sinks.
Green LED Drive Outputs. G0–G7 are open-drain, constant-current sinks.
Positive Supply Voltage. Bypass VDD to GND with a 0.1µF ceramic capacitor.
Serial-Interface Load CMOS Output
Serial-Interface Inverting Data LVDS Output
Serial-Interface Noninverting Data LVDS Output
PWM and Serial-Interface Inverting Clock LVDS Output
PWM and Serial-Interface Noninverting Clock LVDS Output
Multiplex 1 Active-Low, Open-Drain Output. Use MUX1 to drive a pnp transistor.
Analog Ground. Connect to GND.
Blue LED Drive Outputs. B0 to B7 are open-drain, constant-current sinks.
Power Ground. Exposed pad on package underside must be connected to GND.
_______________________________________________________________________________________ 5

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MAX6974 arduino
24-Output PWM LED Drivers
for Message Boards
169DEC, setting the port output current level to 21.8mA.
The global-intensity PDM value is set to 96DEC, producing
an even distribution of ON subframes out of the 128
possible (shown in Figure 4 as subframes 1, 3, 4, 5, etc).
Each subframe can be ON for a PWM duration set by the
individual PWM value. The PWM value setting of
2560DEC out of 4096 (12-bit) results in a further reduction
of current ON time (shown in bold trace).
The internal PDM logic spreads the on subframes as
evenly as possible among the off subframes to keep
the effective scanning frequency high.
For applications with a slower clock speed, the
MAX6975 can increase the display refresh rate by a
factor of four to eliminate visible flicker. Setting configu-
ration bit D4 (GLB4) to 1 activates the increased
refresh rate (see Table 6). The increased refresh rate
reduces the number of global-intensity settings by a
factor of four (see Table 3).
MAX6974 Video-Frame Timing
The MAX6974 supports up to 60 video frames per
second (fps). The following equation shows the
required clock frequency to support 60 video fps:
60 (video fps) x 4096 (clocks per 12-bit PWM period) x
128 (global-intensity subframes) = 31.5MHz.
The MAX6974 supports up to a 33MHz clock signal
(~63fps).
Each 12-bit PWM period contains 4096 clock cycles;
multiply that number by 128 (number of global-intensity
subframes) to obtain the required number of clock cycles
(524,288) per video frame. The MAX6974 requires 36
bits (12 bits per color multiplied by three colors) to drive
an RGB pixel. The maximum pixel data that the
MAX6974 can send per video frame is 524,288 / 36 or
14,563 pixels, corresponding to 1820 cascaded
MAX6974s.
MAX6975 Video-Frame Timing
The MAX6975 also supports up to 60 video frames per
second (fps). The following equation shows the
required clock frequency to support 60 video fps:
60 (video fps) x 16,384 (clocks per 14-bit PWM period)
x 32 (global-intensity subframes) = 31.5MHz.
The MAX6975 supports up to a 33MHz clock signal
(~63fps).
Each 14-bit PWM period contains 16,384 clock cycles;
multiply 16,384 by 32 (global-intensity subframes) to
obtain the required number of clock cycles (524,288)
per video frame. The MAX6975 requires 42 bits (14 bits
per color multiplied by three colors) to drive an RGB
pixel. The maximum pixel data that the MAX6975 can
send per video frame is 524,288 / 42 or 12,483 pixels,
corresponding to 1560 cascaded MAX6975s.
(mA)
30mA MAX
25
PWM = 2560/4096
169d = 20
OUTPUT LED CURRENT
GLOBAL PDM = 96/128 SUBFRAMES
15
10
6mA MIN
5
ON ON ON ON ON ON ON
0123456789
ONE FRAME IS 219 (524,288) CLKI CYCLES LONG
SUBFRAME NUMBER
10
ON
11
Figure 4. The three levels of LED current control (CALDAC, global-intensity PDM, and individual PWM) modulate the average output
current.
______________________________________________________________________________________ 11

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