MAX6967 MAXIM [Maxim Integrated Products], MAX6967 Datasheet - Page 20

• Manufacturer Part Number: MAX6967
• Description: 10-Port Constant-Current LED Drivers and I/O Expanders with PWM Intensity Control
• Manufacturer: MAXIM [Maxim Integrated Products]

10-Port Constant-Current LED Drivers and I/O
Expanders with PWM Intensity Control
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
Table 10. Ramp-Up Register Format
Figure 6. Output Fade DAC (Global Current = 0x07)
20
Write ramp-up
Read ramp-up
Ramp-up time (f
Instant full current coming out from shutdown
1/16s ramp-up to full current coming out from shutdown
1/8s ramp-up to full current coming out from shutdown
1/4s ramp-up to full current coming out from shutdown
1/2s ramp-up to full current coming out from shutdown
1s ramp-up to full current coming out from shutdown
2s ramp-up to full current coming out from shutdown
4s ramp-up to full current coming out from shutdown
CURRENT
17.5mA
12.5mA
7.5mA
2.5mA
20mA
15mA
10mA
0mA
5mA
______________________________________________________________________________________
PORT CURRENT = FULL
PORT CURRENT = HALF
CURRENT
FULL
FADE-UP
CURRENT
7/8
PWM
CURRENT
6/8
= 32768Hz)
REGISTER
CURRENT
5/8
CURRENT
4/8
CURRENT
3/8
CURRENT
FADE-OFF
2/8
CURRENT
1/8
CURRENT
ZERO
R/W
X
X
X
X
X
X
X
X
0
1
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.
Figure 7. Global Current Modifies Fade Behavior
ADDRESS
CODE
(HEX)
0x12
CURRENT
17.5mA
12.5mA
2.5mA
20mA
7.5mA
15mA
10mA
0mA
5mA
GLOBAL CURRENT = 0x07
GLOBAL CURRENT = 0x06
GLOBAL CURRENT = 0x05
GLOBAL CURRENT = 0x04
GLOBAL CURRENT = 0x03
GLOBAL CURRENT = 0x02
GLOBAL CURRENT = 0x01
GLOBAL CURRENT = 0x00
CURRENT
FULL
FADE-UP
D7
X
X
X
X
X
X
X
X
X
0
CURRENT
7/8
D6
X
X
X
X
X
X
X
X
X
0
CURRENT
6/8
D5
CURRENT
X
0
X
X
X
X
X
X
X
X
REGISTER DATA
5/8
D4
CURRENT
X
0
X
X
X
X
X
X
X
X
4/8
CURRENT
D3
3/8
X
0
X
X
X
X
X
X
X
X
CURRENT
D2
2/8
FADE-OFF
0
0
0
0
1
1
1
1
Ramp-up
CURRENT
1/8
D1
0
0
1
1
0
0
1
1
ZERO
CURRENT
D0
0
1
0
1
0
1
0
1