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MAX17061

Full-Scale LED Brightness

in DPWM Dimming Control

The full-scale LED current in the DPWM dimming is

determined by resistance from the ISET pin to ground:

The acceptable resistance range is 133kΩ < R

ISET

266kΩ, which corresponds to full-scale LED current of

30mA > I

LEDMAX

> 15mA. Connect ISET to V

for a

default full-scale LED current of 25mA.

The current source output is pulse-width modulated

and synchronized with a DPWM signal to reduce jitter

and flicker noise in the display.

DPWM Frequency Setting

The MAX17061 uses an internal DPWM signal to perform

dimming control. The DPWM frequency is specified by

an external resistor connected from FSET pin to GND:

where: α = 10.638

γ = 58509

The adjustable range for the FSET resistor, R

FSET

, is

from 42kΩ to 464kΩ, corresponding to the DPWM fre-

quency of 200Hz to 2kHz.

Dimming Control Interfaces

The MAX17061’s dimming control circuit consists of

two interfaces: PWM and SMBus. The block diagram of

these two input interfaces is shown in Figure 5. The

dimming can be performed in three modes: PWM,

SMBus, or DPST. In PWM mode, the brightness is

adjusted by the PWM signal applied to the PWMI pin. In

SMBus mode, the brightness is adjusted by an I

command from uplink processor through the 2-wire

SMBus. In DPST mode, the brightness is adjusted by

the product of the PWM duty cycle and SMBus com-

mand value. This DPWM control provides a dimming

range with 8-bit resolution down to 2.7% and supports

Intel DPST to maximize battery life.

DPWM

×+

αγ[]Ω

mA k

LEDMAX

ISET

×20 200 Ω

8-String White LED Driver with

SMBus for LCD Panel Applications

16 ______________________________________________________________________________________

PWMI

PWMO

BUFFER

MUX

0x03

IDENTIFICATION

< = 1

SCL

SMBus

INTERFACE

DPWM

SETTING

DIGITAL

MULTIPLIER

BACKLIGHT

ON/OFF

SDA

0x02 0x01 0x00

MUX

PWM_SEL

PWM_MD

SMBus AND PWM INPUT BLOCK

FAULT/STATUS

DEVICE

CONTROL

BRIGHTNESS

CONTROL

Figure 5. MAX17061 PWM and SMBus Interface Circuit

D = 30%

D = 12.5%

D = 6.25%

DPWM

LEDMAX

LED

D = 50%

D =

DPWM

DPWM DIMMING MODE

Figure 4. LED Current Control by DPWM Signal in Dimming

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 25 26

MAX17061 1

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