MAX8648 Maxim Integrated Products, MAX8648 Datasheet - Page 12

• Manufacturer Part Number: MAX8648
• Description: (MAX8647 / MAX8648) Ultra-Efficient Charge Pumps
• Manufacturer: Maxim Integrated Products

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Ultra-Efficient Charge Pumps for
Six White/RGB LEDs in 3mm x 3mm Thin QFN
Ceramic capacitors are recommended due to their small
size, low cost, and low ESR. Select ceramic capacitors
that maintain their capacitance over temperature and
DC bias. Capacitors with X5R or X7R temperature char-
acteristics generally perform well. Recommended val-
ues are shown in the Typical Operating Circuit . Using a
larger value input capacitor helps to reduce input ripple
(see the Input Ripple section).
It is not necessary for the LED anodes to connect to IN.
Figure 7 shows an example using separate supplies to
power the LED_ groups of the MAX8648. In this exam-
ple, the voltage source (V1) provides power for RGB
LEDs (LED1, LED2, and LED3). V2 provides power for
backlight LEDs (LED4 and LED5), and V3 provides
power for a red charge indicator (LED6).
The MAX8647/MAX8648 have a high-frequency,
switched-capacitor voltage inverter. For best circuit per-
formance, use a solid copper plane and place C1–C4 as
close as possible to the MAX8647/MAX8648. Figure 4
shows the MAX8648 evaluation kit example layout.
12
Figure 3. EN_ Timing Diagram
______________________________________________________________________________________
I
LED_
EN
_
Driving LEDs with Multiple Supplies
0mA
0
INITIAL t
> 120μs
HI
PCB Layout and Routing
24mA
1
Capacitor Selection
22.4
2
20.8
3
19.2
4
17.6
5
16.0
t
1μs TO 500μs
LO
0.6
PROCESS: BiCMOS
Figure 4. MAX8648 Evaluation Kit Layout for C1–C4
26
0.5
27
0.4
t
> 1μs
HI
28
0.3
29
0.2
30
0.1mA
31
24mA 22.4
Chip Information
t
SHDN
4ms
0mA