Rainbow Electronics MAX6975 - Manual (Page 12)

MAX6974/MAX6975
Multiplexed vs. Nonmultiplexed Operation
The MAX6974/MAX6975 can double the number of
LEDs driven from 24 to 48 through multiplexing. When
multiplexing, the two outputs, MUX0 and MUX1, drive
two external pnp transistors, such as FMMTL717, used
as common-anode power switches (see
Figure 5).
24-Output PWM LED Drivers
for Message Boards
12 ______________________________________________________________________________________
R0 R1 R2 R3 R4 R5 R6 R7
(REDS)
(REDS)
(GREENS)
(GREENS)
(BLUES)
(BLUES)
Q1
FMMTL717
R1
560
Ω
R2
180
Ω
C1
120pF
+5.55V
Q2
FMMTL717
R1
560
Ω
R2 180
Ω
C1 120pF
G1 G2 G3 G4 G5 G6 G7 G0 B1 B2 B3 B4 B5 B6 B7 B0
MUX0 MUX1
SUBFRAME 15
MUX1
16,384 CLKs
SUBFRAME 0
MUX0
16,384 CLKs
SUBFRAME 0
MUX1
16,384 CLKs
SUBFRAME 1
MUX0
16,384 CLKs
SUBFRAME 1
MUX1
16,384 CLKs
SUBFRAME 14
MUX0
16,384 CLKs
SUBFRAME 14
MUX1
16,384 CLKs
SUBFRAME 15
MUX0
16,384 CLKs
SUBFRAME 15
MUX1
16,384 CLKs
SUBFRAME 0
MUX0
16,384 CLKs
ONE COMPLETE 524,288 CLOCK CYCLE MUL
TIPLEXED VIDEO FRAME
Figure 5. MAX6975 Multiplexing Two Sets of Eight RGB Pixels with a Single LED Supply and Subframe Timing