Rainbow-electronics MAX8645Y Bedienungsanleitung PDF herunterladen (Seite 12)

MAX8645X/MAX8645Y

1x/1.5x/2x White LED Charge Pumps with Two

LDOs in 4mm x 4mm TQFN

12 ______________________________________________________________________________________

Input Ripple

For LED drivers, input ripple is more important than out-

put ripple. Input ripple is highly dependent on the

source supply’s impedance. Adding a lowpass filter to

the input further reduces input ripple. Alternately,

increasing C

to 22µF cuts input ripple in half with only

a small increase in footprint. The 1x mode always has

very low input ripple.

Typical operating waveforms shown in the Typical

Operating Characteristics show input ripple current in

1x, 1.5x, and 2x modes.

LDO Output Voltage Selection (P1 and P2)

As shown in Table 2, the LDO output voltages, LDO1

and LDO2 are pin programmable by the logic states of

P1 and P2. P1 and P2 are tri-level inputs: IN, open, and

GND. The input voltage, V

, must be greater than the

selected LDO1 and LDO2 voltages. The logic states of

P1 and P2 can be programmed only during ENLDO

low. Once the LDO_ voltages are programmed, their

values do not change by changing P1 or P2 during

ENLDO high.

Component Selection

Use only ceramic capacitors with an X5R, X7R, or better

dielectric. See Table 3 for a list of recommended parts.

Connect a 1µF ceramic capacitor between LDO1 and

GND, and a second 1µF ceramic capacitor between

LDO2 and GND for 200mA applications. The LDO out-

put capacitor’s (C

LDO

) equivalent series resistance

(ESR) affects stability and output noise. Use output

capacitors with an ESR of 0.1Ω or less to ensure stability

and optimum transient response. Connect C

LDO_

close as possible to the MAX8645X/MAX8645Y to mini-

mize the impact of PCB trace inductance.

MAX8645X

MAX8645Y

1μF

10μF

0.01μF

10μF

GND

OUT

MAIN FLASH

OUTPUT

UP TO 240mA

1μF

LDO1

LDO2

C2P C2N

1μF

C1P C1N

REFBPSETM SETF PGND

ON/OFF AND

VOLTAGE

SELECTION

INPUT

2.7V TO 5.5V

ENM2

ENM1

ENF

ENLDO

4.12kΩ

6.81kΩ

Figure 4. Schematic for When Fewer than 8 LEDs Are Acceptable

MAX8645X MAX8645Y

P1 P2

LDO1 (V) LDO2 (V)

IN IN 3.3 1.8 2.8 2.6

IN OPEN 3.0 1.5 2.8 2.8

IN GND 2.8 1.5 2.9 1.5

OPEN IN 3.3 1.5 2.6 1.9

OPEN OPEN 2.6 1.8 2.6 2.6

OPEN GND 2.6 1.5 2.8 1.9

GND IN 3.0 1.8 2.9 1.8

GND OPEN 2.8 1.8 2.9 1.9

GND GND 2.5 1.8 2.9 2.9

Table 2. P1 and P2, LDO Output Voltage

Selection

1 2 ... 7 8 9 10 11 12 13 14 15

Kommentare zu diesen Handbüchern

Keine Kommentare

Rainbow-electronics MAX8645Y Bedienungsanleitung Seite 12

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Schalttafel Rainbow-electronics MAX8645Y