Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
2
Table 2. I C Control Data Byte—Device Address 0x9A
SDA CONTROL BYTE
COMMAND
DATA
D2
FUNCTION
Not used
C2
0
C1
0
C0
0
D4
D3
D1
D0
—
—
—
—
—
LED1 current
LED2 current
LED3 current
LED4 current
LED5 current
LED6 current
Not used
0
0
1
24.0mA to 0.1mA and off in 32 steps
24.0mA to 0.1mA and off in 32 steps
24.0mA to 0.1mA and off in 32 steps
24.0mA to 0.1mA and off in 32 steps
24.0mA to 0.1mA and off in 32 steps
24.0mA to 0.1mA and off in 32 steps
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
—
—
—
—
—
Note: C2 is MSB and D0 is LSB. The power-on default settings for D4 to D0 are all 0, which indicates that all LED_ are off.
2
6
Table 3. MAX8647 I C Data vs. LED Currents
D4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
D3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
D2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
D1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
D0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
mA
D4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
D3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
D2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
D1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
D0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
mA
2.8
2.4
2
24
22.4
20.8
19.2
17.6
16
1.6
1.4
1.2
1
14.4
12.8
11.2
9.6
8
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
OFF
6.4
5.6
4.8
4
3.2
Temperature Derating Function
Power-Up LED Detection and
Fault Protection
The MAX8647/MAX8648 contain a derating function that
automatically limits the LED current at high temperatures
to help protect the LEDs from damage. 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. The derating circuit
lowers the LED current at approximately 2.5%/°C once
the IC is above +60°C. The typical derating function
characteristic is shown in the Typical Operating
Characteristics.
The MAX8648 contains special circuitry to detect short-
circuit conditions at power-up and disable the corre-
sponding current regulator to avoid wasting battery
current. Connect any unused LED_ to IN to disable the
corresponding current regulator. If an LED fails short
circuit, the current regulator continues the current regu-
lated operation until power to the IC is cycled and the
short circuit is detected. An open-circuit LED failure dri-
ves the voltage on the corresponding LED_ output
10 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
