Output pwm led drivers for message boards, Multiplexed vs. nonmultiplexed operation – Rainbow Electronics MAX6975 User 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