Datasheet

10-Port Constant-Current LED Drivers and I/O
Expanders with PWM Intensity Control
REGISTER DATA
REGISTER
R/W
ADDRESS
CODE
(HEX)
D7 D6 D5 D4 D3 D2 D1
D0
Write ramp-up 0
XXXXX
Read ramp-up 1
00000
Ramp-up
Ramp-up time (f
PWM
= 32768Hz)
Instant full current coming out from shutdown X
XXXXX00
0
1/16s ramp-up to full current coming out from shutdown X
0x12
XXXXX00
1
1/8s ramp-up to full current coming out from shutdown X
XXXXX01
0
1/4s ramp-up to full current coming out from shutdown X
XXXXX01
1
1/2s ramp-up to full current coming out from shutdown X
XXXXX10
0
1s ramp-up to full current coming out from shutdown X
XXXXX10
1
2s ramp-up to full current coming out from shutdown X
XXXXX11
0
4s ramp-up to full current coming out from shutdown X
XXXXX11
1
Table 10. Ramp-Up Register Format
Ramp-up and ramp-down use the PWM clock for timing.
If the external oscillator is selected, then this clock
should be provided until the end of the sequence. If the
internal oscillator is selected, it always runs during a
fade sequence, even if none of the ports are using PWM.
The ramp-up and ramp-down circuit operates a 3-bit
DAC. The DAC adjusts the internal current reference
used to set the constant-current outputs in a similar
manner to the global current register (Table 8).
Because it is the master current reference that is
scaled, all output constant-current and PWM settings
are adjusted at the same ratio with respect to each
other. This means that LEDs are always faded at the
same rate even if their different intensity settings are
totally different. Figure 6 shows output fade DAC.
The maximum port output current set by the global cur-
rent register (Table 8) also sets the point during ramp-
down that the current starts falling, and the point during
ramp-up that the current stops rising. Figure 7 shows
the ramp waveforms that occur with different global
current register settings.
20mA
15mA
10mA
5mA
0mA
CURRENT
FADE-UP
FULL
CURRENT
7/8
CURRENT
6/8
CURRENT
5/8
CURRENT
4/8
CURRENT
3/8
CURRENT
2/8
CURRENT
1/8
CURRENT
ZERO
CURRENT
17.5mA
12.5mA
7.5mA
2.5mA
PORT CURRENT = HALF
FADE-OFF
PORT CURRENT = FULL
Figure 6. Output Fade DAC (Global Current = 0x07)
20mA
15mA
10mA
5mA
0mA
CURRENT
FULL
CURRENT
7/8
CURRENT
6/8
CURRENT
5/8
CURRENT
4/8
CURRENT
3/8
CURRENT
2/8
CURRENT
1/8
CURRENT
ZERO
CURRENT
17.5mA
12.5mA
7.5mA
2.5mA
FADE-UP
FADE-OFF
GLOBAL CURRENT = 0x07
GLOBAL CURRENT = 0x06
GLOBAL CURRENT = 0x05
GLOBAL CURRENT = 0x04
GLOBAL CURRENT = 0x03
GLOBAL CURRENT = 0x02
GLOBAL CURRENT = 0x01
GLOBAL CURRENT = 0x00
Figure 7. Global Current Modifies Fade Behavior
MAX6966/MAX6967
20
Maxim Integrated