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General Description

The MAX6972/MAX6973 precision current-sinking,

16-output PWM LED drivers drive red, green, and/or blue

LEDs for full-color graphic message boards and video

displays. Each output has an individual 12-bit (MAX6972)

or 14-bit (MAX6973) PWM-intensity (hue) control and

7-bit (MAX6972) or 5-bit (MAX6973) global PWM intensity

(luminance) control. The MAX6972/MAX6973 also fea-

ture open-circuit LED fault-detection circuitry, as well as

a watchdog timer.

The driver has two banks of eight outputs, with each bank

intended to drive a different color in RGB applications.

The standard application uses three MAX6972/

MAX6973s to drive eight RGB LEDs. The full-scale current

for each bank of eight outputs is adjustable from 11mA

to 55mA in 256 steps (0.3125% per step) to calibrate

each color.

The MAX6972/MAX6973 can optionally multiplex by

using outputs MUX0 and MUX1, which each drive an

external pnp transistor. Multiplexing doubles the

MAX6972/MAX6973 drive capability to 32 LEDs.

The MAX6972/MAX6973 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 MAX6972/MAX6973 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 MAX6972/MAX6973 are available in 32-pin TQFN

packages and operate over the -40°C to +125°C

temperature range.

Refer to the MAX6974/MAX6975 data sheet for a

24-output, 6mA to 30mA 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

Features

♦ 16 LED Current Sink Outputs (Two Banks of Eight

Outputs)

♦ 32 LED Drive Option When Multiplexing

♦ 33MHz Clock Supports Up to 63 Frames per

Second of Video

♦ Constant Output Current Calibration from 11mA

to 55mA in 256 Steps

♦ EZCascade™ Interface Simplifies Multiple Driver

Cascading Without External Buffers

♦ 12-Bit or 14-Bit Individual PWM LED Intensity

Controls

♦ 7-Bit or 5-Bit Panel PWM-Intensity Control

♦ +3V to +7V LED Power Supply

♦ +3.0V to +3.6V Logic Supply

♦ Open-Circuit LED Fault Detection

♦ Optional Watchdog Timer Blanks Display if

Interface Fails

♦ Standard -40°C to +125°C Operating Temperature

Range

MAX6972/MAX6973

16-Output PWM LED Drivers

for Message Boards

________________________________________________________________ Maxim Integrated Products 1

MAX6972ATJ

MAX6973ATJ

TQFN

5mm x 5mm

TOP VIEW

MUX0

CLKI-

DIN+

DIN-

LOADI

MUX1

CLKO-

DOUT+

AGND

DOUT-

LOAD0

4567

2324 22 20 19 18

CLKI+

CLKO+

EP*

*EP = EXPOSED PADDLE.

I.C.

Pin Configuration

Ordering Information

19-0534; Rev 0; 5/06

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.

PART

TEMP RANGE

PIN-

PACKAGE

PKG

CODE

MAX6972ATJ+

-40°C to +125°C 32 TQFN-EP*

T3255-5

MAX6973ATJ+

-40°C to +125°C 32 TQFN-EP*

T3255-5

Typical Operating Circuit appears at the end of data sheet.

*EP = Exposed paddle.

+Denotes lead-free package.

Summary of content (23 pages)

PAGE 1
9-0534; Rev 0; 5/06 16-Output PWM LED Drivers for Message Boards Features The MAX6972/MAX6973 precision current-sinking, 16-output PWM LED drivers drive red, green, and/or blue LEDs for full-color graphic message boards and video displays. Each output has an individual 12-bit (MAX6972) or 14-bit (MAX6973) PWM-intensity (hue) control and 7-bit (MAX6972) or 5-bit (MAX6973) global PWM intensity (luminance) control.
PAGE 2
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards ABSOLUTE MAXIMUM RATINGS (All voltages with respect to GND.) VDD ........................................................................-0.3V to +4.0V Y0–Y7, Z0–Z7, MUX0, and MUX1 .........................-0.3V to +8.0V All Other Pins..............................................-0.3V to (VDD + 0.3V) Continuous Power Dissipation (TA = +70°C) 32-Pin TQFN (derate 34.5mW/°C over +70°C) ..........2857mW Operating Temperature Range .................
PAGE 3
16-Output PWM LED Drivers for Message Boards (VDD = 3.0V to 3.6V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VDD = 3.3V, TA = +85°C.) (Note 1) PARAMETER SYMBOL Output Low Voltage MUX_ VOLM Open-Circuit Detection VOCD Output Slew Time Y0–Y7, Z0–Z7 CONDITIONS MIN TYP ISINK = 40mA 0.
PAGE 4
Typical Operating Characteristics (VDD = 3.3V, TA = +25°C, unless otherwise noted.) fCLKI = 32MHz CALDAC = 0xFF fCLKI = 0MHz CALDAC = 0x00 23 TA = -40°C TA = +25°C TA = -40°C IDD (mA) IDD (mA) 45 25 MAX6972/73 toc01 47 OPERATING CURRENT CONSUMPTION vs. SUPPLY VOLTAGE VDD 43 MAX6972/73 toc02 OPERATING CURRENT CONSUMPTION vs. SUPPLY VOLTAGE VDD TA = +25°C 21 19 TA = +125°C 41 TA = +125°C 15 3.1 3.2 3.3 3.4 3.5 3.6 3.0 3.1 3.2 3.3 3.4 3.
PAGE 5
16-Output PWM LED Drivers for Message Boards PIN NAME 1,17 VDD FUNCTION 2 MUX0 3 CLKI+ PWM and Serial-Interface Noninverting Clock LVDS Input 4 CLKI- PWM and Serial-Interface Inverting Clock LVDS Input 5 DIN+ Serial-Interface Noninverting Data LVDS Input 6 DIN- Serial-Interface Inverting Data LVDS Input 7 LOADI 8 I.C. Positive Supply Voltage. Bypass VDD to GND with a 0.1µF ceramic capacitor. Multiplex 0 Active-Low, Open-Drain Output. Use MUX0 to drive a pnp transistor.
PAGE 6
16-Output PWM LED Drivers for Message Boards MAX6972/MAX6973 MAX6972 Block Diagram Y LED OUTPUT Y7 Y6 Y5 Y4 Y3 Y2 Y1 Y0 EXT.
PAGE 7
16-Output PWM LED Drivers for Message Boards Y LED OUTPUT Y7 Y6 Y5 Y4 Y3 Y2 Y1 Y0 EXT.
PAGE 8
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards LED outputs are grouped in ports (Y and Z) with eight LED outputs per port. Each port features its own current calibration control DAC (CALDAC) with 0.31% resolution to set the current. The MAX6972/MAX6973 current calibration feature allows unmatched LEDS from different lots and manufacturers to be color matched.
PAGE 9
16-Output PWM LED Drivers for Message Boards Global-Intensity Control The MAX6972/MAX6973 adjust global and individual intensities over a time period called a frame. One frame requires 2 19 (524,288) periods of CLKI and corresponds to one video-frame time. Video frames generally contain consecutive images displayed rapidly to yield a motion picture display. Running the MAX6972/ MAX6973 at f CLKI = 31.
PAGE 10
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards The MAX6972 subdivides each subframe by 4096 (12-bit) PWM steps and has 16 cycle off zones, leaving an active PWM region of 4064 PWM steps ranging from 16 to 4079. The MAX6973 subdivides each subframe by 16,384 (14-bit) PWM steps and has 32 cycle off zones, leaving an active PWM region of 16,320 PWM steps ranging from 32 to 16,351. The PWM phase for outputs Y0, Y2, Y4, Y6 and Z0, Z2, Z4, Z6 use phasing with the outputs on first and off second.
PAGE 11
16-Output PWM LED Drivers for Message Boards 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 MAX6973 can increase the display refresh rate by a factor of four to eliminate visible flicker. Setting configuration bit D4 (GLB4) to 1 activates the increased refresh rate (see Table 6).
PAGE 12
Multiplexed vs. Nonmultiplexed Operation multiplexing, the two outputs, MUX0 and MUX1, drive two external pnp transistors, such as FMMTL717, used as common-anode power switches (see Figure 5).
PAGE 13
16-Output PWM LED Drivers for Message Boards PART MUX BIT OPERATION 0 Nonmultiplex 1 Multiplex 0 Nonmultiplex 1 Multiplex MAX6972 MAX6973 PART MAX6972 PWM RES. TOTAL CLOCKS PER PWM SUBFRAME USEABLE CLOCKS PER PWM SUBFRAME MAXIMUM PWM DUTY CYCLE 12 bits 4096 4064 4064 / 4096 = 99.22% 14 bits 16,384 16,320 16,320 / 16,384 = 99.61% GLB4 BIT MUX BIT OPERATION GLOBAL PDM RES.
PAGE 14
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards Commands The MAX6972/MAX6973 have four commands used to load all operating mode and LED output current data. Each command is uniquely identified by two bits, C1 and C0, embedded in the serial-interface protocol structure. The commands Load CALDAC, Load GlobalIntensity PDM, and Load Configuration each require 16 bits of data (2 bytes) for every cascaded device.
PAGE 15
16-Output PWM LED Drivers for Message Boards Serial Interface The MAX6972/MAX6973 feature a fully synchronous and fully buffered serial interface that allows cascading of multiple devices. The serial interface consists of inputs (CLKI, DIN, and LOADI) and outputs (CLKO, DOUT, and LOADO). The MAX6972/MAX6973 can pass different data to each cascaded device without any additional inputs to identify the position of the devices in the cascaded chain. Table 6.
PAGE 16
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards The serial interface uses the continuously running clock, CLKI, to synchronously transfer and latch data (33MHz max). The MAX6972/MAX6973 sample inputs DIN and LOADI on the rising edge of CLKI and update outputs DOUT and LOADO on the edge of CLKI. The MAX6972/MAX6973 specifications guarantee that cascaded devices observe setup and hold timing from device to device, making external buffers and clock trees unnecessary, even in very large systems.
PAGE 17
16-Output PWM LED Drivers for Message Boards between CLKI and DIN with the LOADI signal. The synchronization pattern must be 0xE8. CMD[5:0] Send command bits C1 and C0 three times in succession. The command bits define how many data bits are received and where the data is loaded. The four commands are: Header Segment The 24-bit header segment consists of an 8-bit fixed synchronization pattern (SYNC), a 6-bit command pattern (CMD), and a 10-bit counter (CNTR) segment (see Table 7).
PAGE 18
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards Data Segment The bit length of the data segment received by the MAX6972/MAX6973 is dependent on the command specified in the header. The load CALDAC command has two unique data bytes, while load global-intensity PDM and load configuration each have one byte of data repeated once. The CALDAC data within the command load CALDAC is sent with Z CALDAC data first followed by Y CALDAC data, as shown in Table 8.
PAGE 19
16-Output PWM LED Drivers for Message Boards MAX6972/MAX6973 1 CLKO DOUT LOADO CLK0 CLKI D0 DIN LOAD0 LOADI MAX6972/MAX6973 2 CLK1 CLKI DOUT D1 DIN LOADO LOAD1 CLKO LOADI MAX6972/MAX6973 HOST MAX6972/MAX6973 3 CLKO CLK2 CLKI DOUT D2 DIN LOADO LOAD2 CLKO LOADI CLK3 DOUT D3 LOADO LOAD3 LOADI DIN CLKI Figure 8.
PAGE 20
MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards the 12-bit or 14-bit PWM data for each of the 16 outputs (see Figure 11). The various data segment bit lengths for each of the four commands and different operating modes is shown in Table 4. Data capturing is the same as described above with the header segment outputs and data being delayed by the full length of the data bit stream being captured plus one clock cycle.
PAGE 21
16-Output PWM LED Drivers for Message Boards For best output current accuracy, design VO to be at least 1.2V: R1(MAX) = (3.15 - 1 - 1.2) / 0.055 = 17.3Ω, so choose R1 = 15Ω hence, VO(MIN) = 3.15 - 1 - (15 x 0.055) = 1.325V and VO(MAX) = 3.45 - 0.7 - (15 x 0.055) = 1.925V. +3.3V Driving LEDs from a Supply Higher than 7V An external npn transistor in a cascode configuration extends the output drive voltage above 7V.
PAGE 22
Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) QFN THIN.EPS MAX6972/MAX6973 16-Output PWM LED Drivers for Message Boards D2 D MARKING b CL 0.10 M C A B D2/2 D/2 k L AAAAA E/2 E2/2 CL (NE-1) X e E DETAIL A PIN # 1 I.D. e/2 E2 PIN # 1 I.D. 0.35x45° e (ND-1) X e DETAIL B e L1 L CL CL L L e e 0.10 C A C 0.
PAGE 23
16-Output PWM LED Drivers for Message Boards COMMON DIMENSIONS EXPOSED PAD VARIATIONS PKG. 16L 5x5 20L 5x5 28L 5x5 32L 5x5 40L 5x5 SYMBOL MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. A A1 A3 b D E e PKG. CODES 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0 0.02 0.05 0 0.02 0.05 0 0.02 0.05 0 0.02 0.05 0 T1655-2 T1655-3 T1655N-1 T2055-3 D2 3.00 3.00 3.00 3.00 3.00 T2055-4 T2055-5 3.15 T2855-3 3.15 T2855-4 2.60 T2855-5 2.60 3.