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MAX6972

16-Output PWM LED Drivers for Message Boards

Maxim Integrated 

16-Output PWM LED Drivers

for Message Boards

through the cascaded devices. When LOADI is low, the

MAX6972/MAX6973 continuously monitor DIN for

reception of the SYNC pattern (see the Header

Segment section).

Header Segment

The 24-bit header segment consists of an 8-bit fixed

synchronization pattern (SYNC), a 6-bit command pat-

tern (CMD), and a 10-bit counter (CNTR) segment (see

Table 7). LOADI must change from low to high within

plus or minus one clock cycle of the first command bit.

When the SYNC bit pattern 0xE8 is recognized, LOADI

is monitored for the rising edge, allowing the device to

internally synchronize LOADI to CLKI. The six command

bits, CMD[5:0], consist of bits C1 and C0 repeated

three times. The four commands used by the MAX6972/

MAX6973 are defined by the two bits, C1 and C0.

The counter segment is incremented by one for each

cascaded device with an internal fault detected. Use the

counter segment to collect fault data across the cas-

caded chain.

HDR[23:0]

Complete 24-bit header segment.

SYNC[7:0]

Synchronization bit pattern 0xE8 is recognized by the

MAX6972/MAX6973 during intervals when LOADI is low.

The SYNC bit pattern, followed by the rising edge of

LOADI, internally synchronizes the timing relationship

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 succes-

sion. The command bits define how many data bits are

received and where the data is loaded. The four com-

mands are:

C1:C0

00

01

10

11

COMMAND

Load individual PWM

Load CALDAC

Load global-intensity PDM

Load configuration

CMD[5:0]

000000

010101

101010

111111

CNTR[9:0]

This is the counter for open LED or overtemperature fault

conditions. The host sends the header segment with the

counter value set to zero. The counter value is incre-

mented one count by each device that detects a fault

condition in the cascaded chain. The accumulated count

value returns to the host from the last device in the cas-

cade chain. The command determines which fault type

is incremented to the counter (see LED Open-Circuit and

Overtemperature Detection Counter section):

CMD[1:0] = X0 Overtemperature faults counted

CMD[1:0] = X1 Open LED faults counted

Table 7. Serial-Interface Header

HDR

23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

SYNC

CMD

CNTR

765432101010109876543210

1 1 1 0 1 0 0 0 C1 C0 C1 C0 C1 C0 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0

LOADI

DIN

HEADER

SYNC

COMMAND

COUNTER

DATA

1

0

1 1 1 0 1 0 0 0 C1 C0 C1 C0 C1 C0 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0

CLKI

(CONTINUOUS) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Figure 7. Header-Segment Timing

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