MAX8831EWE+T Datasheet MAX8831EWE+T | P16-P18

MAX8831

MAX8831 Slave Address

The MAX8831 has a 7-bit-long slave address (Figure

9). The eighth bit following the 7-bit slave address is

the R/W bit. It is low for a write command, high for a

read command. The slave addresses available for the

MAX8831 are 1001101X (with a write/read address of

0x9A/0x9B). Contact the factory for other I

C address

options.

Message Format for Writing

A write to the MAX8831 comprises the transmission of

the MAX8831’s slave address with the R/W bit set to

zero (0x9A), followed by at least 1 byte of information.

The first byte of information is the command byte

(Figure 10), which determines which register of the

MAX8831 is to be written by the next byte, if received. If

a STOP condition is detected after the command byte

is received, the MAX8831 takes no further action

beyond storing the command byte. Any bytes received

after the command byte are data bytes. The first data

High-Efficiency, White LED Step-Up Converter

with I

C Interface in 2mm x 2mm WLP

16 ______________________________________________________________________________________

MSB

LSB

R / W

ACK

SCL

SDA

Figure 9. MAX8831 Default Slave Address

7-BIT SLAVE

ADDRESS

0AS

COMMAND

BYTE

DATA BYTE

SSTART BIT

AS ACKNOWLEDGE SLAVE

P STOP BIT

Figure 10. I

C Single-Byte Write

SDA

SCL

DATA LINE STABLE,

DATA IS VALID

CHANGE OF DATA

IS ALLOWED

Figure 7. I

C Bit Transfer

SDA BY

TRANSMITTER

SDA BY

RECEIVER

SCL

NOT ACKNOWLEDGE

ACKNOWLEDGE

CLOCK PULSE FOR

ACKNOWLEDGMENT

START

CONDITION

Figure 8. I

C Acknowledge

MAX8831

High-Efficiency, White LED Step-Up Converter

with I

C Interface in 2mm x 2mm WLP

______________________________________________________________________________________ 17

7-BIT SLAVE

ADDRESS

0AS

COMMAND

BYTE

FIRST DATA BYTE

SSTART BIT

AS ACKNOWLEDGE SLAVE

P STOP BIT

LAST DATA

BYTE

Figure 11. I

C Multiple-Byte Write

7-BIT SLAVE

ADDRESS

0AS

COMMAND

BYTE

SSTART BIT

AS ACKNOWLEDGE SLAVE

P STOP BIT

DATA BYTE

ACKNOWLEDGE MASTER

7-BIT SLAVE

ADDRESS

Figure 12. I

C Single-Byte Read

7-BIT SLAVE

ADDRESS

0AS

COMMAND

BYTE

SSTART BIT

AS ACKNOWLEDGE SLAVE

P STOP BIT

FIRST DATA BYTE

ACKNOWLEDGE MASTER

7-BIT SLAVE

ADDRESS

LAST DATA BYTE

Figure 13. I

C Multiple-Byte Read

byte goes into the internal register of the MAX8831

selected by the command byte. If multiple data bytes

are transmitted before a STOP condition is detected,

these bytes are stored in subsequent MAX8831 internal

registers because the command byte address auto-

increments (Figure 11).

Message Format for Reading

The MAX8831 is read using the MAX8831’s internally

stored command byte as an address pointer, the same

way the stored command byte is used as an address

pointer for a write. The pointer autoincrements after

each data byte is read, using the same rules as for a

write. Thus, a read is initiated by first configuring the

MAX8831’s command byte by writing the command

byte corresponding to the beginning register address

to be read. The master can now read n consecutive

bytes from the MAX8831, by first writing the read com-

mand (0x9B) to the MAX8831 (Figures 12 and 13).

When performing read-after-write verification, reset the

command byte’s address since the stored byte

address is autoincremented after the write.

MAX8831 I

C Registers

The MAX8831 contains 19 registers that are accessible

through the I

C interface (Table 3). See the register

descriptions for more details. The register contents are

reset to the default RESET values (shown in Table 3) if

goes low.

ON/OFF Control Register

The ON/OFF control register (ON/OFF_CNTL) enables

and disables the LED1–LED5 current regulators (Table

4). Write a 1 to the LED#_EN bit to enable that

MAX8831

LED_ current regulator. Write a 0 to the LED#_EN bit to

disable that LED_ current regulator. Overvoltage, open

Schottky diode, and thermal-shutdown faults automati-

cally clear all LED#_EN bits to turn off all LED current

regulators.

LED_ Ramp Control Registers

The LED_ ramp control registers (LED1_RAMP_CNTL

to LED5_RAMP_CNTL) contains the timing information

for each LED current regulator’s ramp-up and ramp-

down rate. The registers at locations 0x03 to 0x07 pro-

gram the ramp rates of the LED1 to LED5 current

regulators, respectively. The ramp-up and ramp-down

rates are programmable with eight different timing

selections. See Table 5.

LED_ Current Control Registers

The LED_ current control registers (ILED1_CNTL to

ILED5_CNTL) program the individual LED1 to LED5

current regulators (see Tables 1 and 2 for programma-

ble values). Registers located at 0x0B and 0x0C pro-

gram the current of the LED1 and LED2 current

regulators (Table 6). Registers located at 0x0D, 0x0E,

and 0x0F program the current of the LED3, LED4, and

LED5 current regulators, respectively (Table 7).

LED3, LED4, and LED5 Blink Control Registers

The blink control registers (LED3_BLINK_CNTL to

LED5_BLINK_CNTL) contain the blink control timing

data for the LED3, LED4, and LED5 current regulators.

The registers allow enabling of the blink function and

control the on- and off-time of the blink sequence. The

registers located at 0x17, 0x18, and 0x19 control the

blink timing of the LED3, LED4, and LED5 current regu-

lators, respectively. See Table 8. The LED1 and LED2

current regulators do not have blink functionality.

Boost Control Register

The boost control register (BOOST_CNTL) determines if

the LED3, LED4, or LED5 current regulators are includ-

ed in the step-up converter regulation loop. If pro-

grammed to be powered from the step-up converter,

LED_ is included in the feedback loop. Otherwise, if

LED_ is programmed to be powered from an alternate

source, LED_ is not included in the feedback loop.

LED3, LED4, and LED5 are high impedance in shut-

down. If the BOOST_CNTL bits are programmed to

power LED3, LED4, or LED5 from an alternate source,

open LED detection is enabled only for that current reg-

ulator. See Table 9. The LED1 and LED2 inputs are

always in the feedback loop and are not programmable

with the boost control register.

LED_ Status Registers

The LED_ status registers (STAT1, STAT2) indicate the

fault conditions of the MAX8831 IC and LEDs and are

read-only registers. The STAT1 register indicates a fault

condition for each LED_ string, whether a shorted or

open LED_ fault is causing the fault condition. The sec-

ond status register, STAT2, reports the following global

system faults: output overvoltage-condition detection

(OVP), thermal-shutdown condition detection (TSD),

and open Schottky diode detection (OSDD). See

Tables 10 and 11. See the

Open/Shorted LED

Detection, Output Overvoltage Protection, Open

Schottky Diode Detection, Thermal-Shutdown

Protection

, and

System States and Fault Handling

sec-

tions for more details.

Chip ID

The CHIP ID registers (CHIP_ID1 and CHIP_ID2) con-

tains MAX8831 die type and mask revision data. These

registers are read-only registers. See Tables 12 and 13.

Applications Information

Inductor Selection

The MAX8831 is optimized for a 10µH inductor,

although larger or smaller inductors can be used.

Using a smaller inductor results in discontinuous cur-

rent-mode operation over a larger range of output

power, whereas use of a larger inductor results in con-

tinuous conduction for most of the operating range.

To prevent core saturation, ensure that the inductor’s sat-

uration current rating exceeds the peak inductor current

for the application. For larger inductor values and contin-

uous conduction operation, calculate the worst-case

peak inductor current with the following formula:

Otherwise, for small values of L in discontinuous con-

duction operation, I

PEAK

is 860mA (typ). Table 14 pro-

vides a list of recommended inductors.

Capacitor Selection

Ceramic X5R or X7R dielectric capacitors are recom-

mended for best operation. When selecting ceramic

capacitors in the smallest available case size for a

given value, ensure that the capacitance does not

degrade significantly with DC bias. Generally, ceramic

capacitors with high values and very small case size

have poor DC bias characteristics.

PEAK

OUT OUT MAX

IN MIN

()

High-Efficiency, White LED Step-Up Converter

with I

C Interface in 2mm x 2mm WLP

18 ______________________________________________________________________________________

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MAX8831EWE+T

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LED Lighting Drivers White LED Step-Up Converter

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