RT9396 datasheet(13/17 Pages) RICHTEK

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RT9396

DS9396-01 April 2011

www.richtek.com

Applications Information

The RT9396 is an I2C interface PMIC with one 6-Channel

charge pump white LEDdriver and four LDOs. The charge

pump provides 6-Channel low dropout voltage current

source to regulate up to 6 white LEDs. For high efficiency,

the RT9396 implements a smart mode transition for charge

pump operation. The four LDOs are capable of delivering

low dropout voltage of 200mV @ 200mA with 3% output

accuracy. The I2C dimming function allows for a 64 steps

LED brightness control and 16 steps LDO voltage control.

Input UVLO

An under voltage lockout (UVLO) function is provided to

prevent unstable occurrences during start-up. The UVLO

threshold is set at an input rising voltage of 2.1V typically

with a hysteresis of 0.2V. The input operating voltage range

of the RT9396 is from 2.8V to 5V. An input capacitor should

be placed near the VIN pin to reduce ripple voltage. It is

recommended to use a ceramic 2.2

μF or larger capacitance

as the input capacitor.

Soft-Start

The RT9396 includes a soft-start circuit to limit the inrush

current at power on and mode switching. The soft-start

circuit limits the input current before the output voltage

reaches a desired voltage level.

Mode Decision

The RT9396 uses a smart mode decision method to

choose the working mode for maximum efficiency. The

charge pump can operate at x1, x1.5 or x2 mode. The

mode decision circuit senses the output voltage and LED

voltage to determine the optimum working mode.

Power Sequence

In order to assure normal operating condition, the input

voltage and ENshould be active before the RT9396 receives

the I2C signal, as shown in Figure 3. The RT9396 can be

shut down by pulling EN low. When EN is reset, the I2C

signal also needs to be re-applied to resume normal

operating condition.

Figure 3. The Power Sequence

SCL

……………

SDA

2C Compatible Interface

Figure 4 shows the timing diagram of the I2C interface.

The RT9396 communicates with a host (master) using

the standard I2C 2-wire interface. The two bus lines of

SCL and SDA must be pulled high when the bus is not in

use. Internal pull-up resistors are installed. After the START

condition, the I2C master sends 8-bits data, consisting of

seven address bits and a following data direction bit (R/

W). The RT9396 address is 1010100 (54h) and is a receive-

only (slave) device. The second word selects the register

to which the data will be written. The third word contains

data to write to the selected register.

Figure 2 shows the writing information for voltage of the

four LDOs and current of the six LEDs. In the second

word, the sub-address of the four LDOs is “001” and the

sub-address of the LEDDriver for different dimming modes

are respectively “010”, “011” and “100”. For the LDO

output voltage setting, bits B1 to B4 represent each LDO

channel respectively where a “1” indicates selected and

a “0” means not selected. The B0 bit controls on/off (1/

0) mode for the selected LDO channel(s). Then, in the

third word, bits C0 to C3 control a 16-step setting of LDO1

to LDO4. The voltage values are listed in Table 1.

For LED dimming, there are three operating modes

(Backlight I, Backlight II and Backlight III) to select from

by writing respectively “010”, “011” and “100” into the

first three bits of the second word. When Backlight I is

selected, all six LEDs have the same behavior. Their 64-

step dimming currents are set by bits C0 to C5, which

are listed in Table 2. The bits C6 and C7 determine the

fade in/out time of each step as shown in Figure 2. For

Backlight II and Backlight III, two sets of LEDs, called

main and Sub, can work separately and turn on solely. It

should be noticed that no matter which mode is selected,

the B0 bit must be a “1” in order for te LEDs in the main

set to be turned on.

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