max8879etg Maxim Integrated Products, Inc., max8879etg Datasheet - Page 12

• Manufacturer Part Number: max8879etg
• Description: Charge Pump For Backlight/flash/rgb Leds With Safety Timer
• Manufacturer: Maxim Integrated Products, Inc.

Table 4. RGB Ramp Rate
The currents for the three sub LEDs are set indepen-
dently, allowing them to drive an RGB LED. The cur-
rent-level settings for both the main and sub LEDs
range from 0.9mA to 30mA, defaulting to 15mA each
(see Tables 1, 2, and 3).
The flash LEDs are controlled by pulsing the FSH input
low. There are two registers in the MAX8879 to set the
flash/movie current level. The Movie register sets the
F1–F4 LED current when the I
activate the LEDs and the Flash register sets the F1–F4
LED current when the FSH input is pulsed low. The cur-
rent level settings for the flash LEDs ranges from 3.3mA
to 100mA, with a default of 25.8mA (see Tables 1, 2,
and 3). The Flash register has priority over the Movie
register when both movie and flash are on. In the event
that the flash safety timer period expires, the flash LEDs
are turned off and the movie mode ON/OFF control
bit is reset to 0. This is to prevent the MAX8879 from
going back into movie mode in the event of a safety
timer violation.
Figure 2. I
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
* Default in bold italics.
12
(HEXADECIMAL)
CONTROL BYTE
SCK
SDA
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
______________________________________________________________________________________
E0
E1
E2
E3
2
t
C Timing Diagram
SU:STA
A
t
HD:STA
RGB RAMP
RATE (A/s)
0.0572
0.0286
t
LOW
0.114
58.6
B
t
HIGH
R A M P TI M E FR O M OF F T O
F U L L BR I G H T N ESS ( m s )
2
C interface is used to
t
SU:DAT
C
0.512
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE (OP/SUS BIT)
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
1048
262
524
D
E
F
The LED cathode connections (M_, S_, and F_) can be
connected together in any combination to allow the use
of higher current LEDs. For example, to drive a single
flash LED at up to 400mA, connect F1, F2, F3, and F4
together to the cathode of the flash LED.
To avoid constantly operating in overvoltage protection
mode, any unused LED cathode connection (M_, S_, or
F_) must be connected to OUT. This disables the corre-
sponding current regulator.
The three sub LED currents are controlled indepen-
dently by the I
mon anode RGB LED. Thirty-two programmable
brightness levels (5 bits) per LED provide a total of 32k
colors. To smooth the transition between different
color/brightness settings, a controlled ramp is used
when the sub LED current level is changed, when the
sub LEDs are enabled, and when the LEDs are dis-
abled. The ramp rate is set to one of four settings with
the I
The MAX8879 contains a temperature-derating function
that automatically limits the LED current at high tempera-
tures in accordance with the recommended derating
curve of popular white LEDs. The derating function
enables the safe usage of higher LED current at room
temperature, thus reducing the number of LEDs required
to backlight the display. In camera-light applications, the
derating circuit protects the LEDs and PC board from
overheating. The derating circuit limits the LED current
t
HD:DAT
2
C interface (see Table 4).
G
RGB Color and Ramp-Rate Settings
2
Temperature-Derating Function
C interface, allowing for use of a com-
H
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
I
J
K
t
SU:STO
L
t
BUF
M