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MAX8847Z

High-Performance Negative Charge Pump for 6 White LEDs in 3mm x 3mm Thin QFN

Maxim Integrated 

MAX8847Y/MAX8847Z

High-Performance Negative Charge Pump

for 6 White LEDs in 3mm x 3mm Thin QFN

PWM Dimming Control

When VIN is above its undervoltage lockout threshold,

UVLO, apply a PWM signal to ENA to set the corre-

sponding WLED current (see Table 1) that is proportional

to the signal duty cycle (0% duty cycle corresponds to

zero LED current and 100% duty cycle corresponds to

full LED current). The allowed PWM frequency range is

from 200Hz to 200kHz. If PWM dimming control is not

required, ENA works as a simple on/off control.

Serial-Pulse Dimming Control (MAX8847Y)

The MAX8847Y uses ENB as a serial-pulse control inter-

face to program the intensity of LED5 and LED6. When

LED5 and LED6 are enabled by driving ENB high, the

MAX8847Y ramps LED5 and LED6 current to 24mA.

Subsequent pulses on ENB reduces the LED5 and LED6

current from 24mA to 0.1mA in 31 steps. After the cur-

rent reaches 0.1mA, the next pulse restores the current

to 24mA. See Table 2 for the LED current values and the

corresponding ENB pulse count. Figure 2 shows a timing

diagram for ENB.

If dimming control is not required, ENB works as a simple

on/off logic control. Drive ENB high for at least 120µs to

enable the LED5 and LED6 current regulators, or drive

ENB low for greater than 8ms (typ) to place the LED5

and LED6 current regulators in shutdown. The LED cur-

rent regulators operate at 100% brightness and off under

these conditions.

0

ENB

INITIAL tHI

tINIT > 120µs

24mA

ILED5/ILED6

SHDN

1

2

3

4

5

26 27 28 29 30 31

tLO

22.4mA

20.8mA

19.2mA

1µs TO 500µs

17.6mA 16.0mA

tHI

> 1µs

tSHDN

24mA

8ms (TYP)

22.4mA

0.6mA 0.5mA 0.4mA 0.3mA 0.2mA 0.1mA

SHDN

Figure 2. Timing Charateristics for LED Serial-Pulse Dimming Control

Table 2. ENB Serial-Pulse Dimming Count and Programmed LED_ Currents

ENB PULSE

COUNT

Startup or ENB high

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

PROGRAMMED LED_ CURRENT

(mA)

24.0

22.4

20.8

19.2

17.6

16.0

14.4

12.8

11.2

9.6

8.0

6.4

5.6

4.8

4.0

3.2

ENB PULSE

COUNT

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PROGRAMMED LED_ CURRENT

(mA)

2.8

2.4

2.0

1.6

1.4

1.2

1.0

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

24.0

10  

Maxim Integrated

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