Rainbow Electronics MAX8848Z User Manual
Page 11
High-Performance Negative Charge Pump
for 7 White LEDs in 3mm x 3mm Thin QFN
MAX8848Y/MAX8848Z
______________________________________________________________________________________ 11
for the LED current values and the corresponding ENA/
ENB pulse count. Figure 2 shows a timing diagram for
ENA/ENB.
If dimming control is not required, ENA/ENB works as
a simple on/off logic control. Drive ENA/ENB high for
at least 120Fs to enable the LED current regulators, or
drive ENA/ENB low for greater than 8ms (typ) to place
the LED current regulators in shutdown. The LED current
regulators operate at 100% brightness and off under
these conditions.
Figure 2. Timing Charateristics for LED Serial-Pulse Dimming Control
Table 2. ENA/ENB Serial-Pulse Dimming Count and Programmed LED_ Currents
EN_
I
LED_
SHDN
INITIAL t
HI
t
INIT
> 120
µ
s
1
µ
s TO 500
µ
s
> 1
µ
s
t
LO
t
HI
SHDN
t
SHDN
8ms (TYP)
24mA
22.4mA
0
1
2
3
4
5
26
27
28
29
30
31
20.8mA 19.2mA 17.6mA
16.0mA
0.6mA 0.5mA
0.4mA 0.3mA 0.2mA
0.1mA
24mA 22.4mA
EN_ PULSE
COUNT
PROGRAMMED LED_ CURRENT
(mA)
EN_ PULSE
COUNT
PROGRAMMED LED_ CURRENT
(mA)
Startup or EN_high
24.0
16
2.8
1
22.4
17
2.4
2
20.8
18
2.0
3
19.2
19
1.6
4
17.6
20
1.4
5
16.0
21
1.2
6
14.4
22
1.0
7
12.8
23
0.8
8
11.2
24
0.7
9
9.6
25
0.6
10
8.0
26
0.5
11
6.4
27
0.4
12
5.6
28
0.3
13
4.8
29
0.2
14
4.0
30
0.1
15
3.2
31
24.0