MAX16826ATJ+ Datasheet MAX16826ATJ+T, MAX16826ATJ+, MAX16826BATJ/V+ | P19-P21

Accessing the MAX16826

The communication between the μC and the MAX16826

is based on the usage of a set of protocols defined on

top of the standard I

C protocol definition. They are

exclusively write byte(s) and read byte(s).

Write Byte(s)

The write byte protocol is as follows:

1) The master sends a START condition.

2) The master sends the 7-bit slave address followed

by a write bit (low).

3) The addressed slave asserts an ACK by pulling

SDA low.

4) The master sends an 8-bit command code.

5) The slave asserts an ACK by pulling SDA low.

6) The master sends an 8-bit data byte.

7) The slave acknowledges the data byte.

8) The master generates a STOP condition or repeats

6 and 7 to write next byte(s).

The command is interpreted as the destination address

(register file unit) and data is written in the addressed

location. The slave asserts a NACK at step 5 if the com-

mand is not valid. The master then interrupts the com-

munication by issuing a STOP condition. If the address

is correct, the data byte is written to the addressed reg-

ister. After the write, the internal address pointer is

increased by one. When the last location is reached, it

cycles to the first register.

Read Byte(s)

The read sequence is:

1) The master sends a START condition.

2) The master sends the 7-bit slave address plus a

write bit (low).

3) The addressed slave asserts an ACK on the data

line.

4) The master sends an 8-bit command byte.

5) The active slave asserts an ACK on the data line.

6) The master sends a repeated START condition.

7) The master sends the 7-bit slave address plus a

read bit (high).

8) The addressed slave asserts an ACK on the data

line.

9) The slave sends an 8-bit data byte.

10) The master asserts a NACK on the data line to

complete operations or asserts an ACK and

repeats 9 and 10.

11) The master generates a STOP condition.

The data byte read from the device is the content of the

addressed location(s). Once the read is done, the inter-

nal pointer is increased by one. When the last location is

reached, it cycles to the first one. If the device is busy or

the address is not correct (out of memory map), the

command code is not acknowledged and the internal

address pointer is not altered. The master then inter-

rupts the communication by issuing a STOP condition.

MAX16826

Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

______________________________________________________________________________________ 19

S ACKSLAVE ADDRESS R/W

7 BITS 0

COMMAND

8 BITS

ACK ACK PDATA

COMMAND BYTE: SELECT REGISTER TO WRITE DATA BYTE DATA GOES INTO THE REGISTER

SET BY THE COMMAND BYTE

8 BITS

WRITE BYTE FORMAT

Figure 7. Write Byte Format

S ACKSLAVE ADDRESS R/W

7 BITS 0

ACKSLAVE ADDRESS R/W

7 BITS 1

COMMAND

8 BITS

ACK SR NACK PDATA

COMMAND BYTE: PREPARE DEVICE FOR

FOLLOWING READ

DATA BYTE DATA COMES FROM THE

8 BITS

READ BYTE FORMAT

Figure 8. Read Byte Format

MAX16826

The register file unit is used to store all the control infor-

mation from the SDA line and configure the MAX16826

for different operating conditions. The register file

assignments of the MAX16826 are in Table 2.

Registers 00h to 03h: String Current Programming

These registers are used to program LED string 1 to

LED string 4 current sink values. For each LED string,

CS1–CS4 inputs are connected to the source of the

external current sink FET and internally are connected

to the inverting input of the internal transconductance

amplifier. The noninverting input of this amplifier is con-

nected to the output of an internal DAC programmed

by these registers. As the DAC is incremented, its out-

put voltage decreases from 316mV to 97mV in 1.72mV

steps by the data written in the register 00h to 03h;

thus, the steady-state voltage at CS1–CS4 is given by

the following formula:

CS1,2,3,4

= 316mV - (1.72mV x RegisterValue[6:0])

For example, if 00h is set to 20h, then the CS1 voltage is:

CS1

= 316mV - 1.72mV x 32 = 265.3mV

Output Programming

Set the switching regulator output voltage by connect-

ing FB to the center of a resistive voltage-divider

between the switching regulator output and GND. V

is regulated to a voltage from 876mV to 1.25V (typ) set

by the register 04h through the I

C interface.

The FB reference voltage can be decreased from 1.25V,

its maximum value, by approximately 2.9mV steps. The

steady-state voltage at FB then is regulated to:

= 1.25V - (2.91mV x 04h[6:0])

Registers 05h to 08h: External Current-Sink

FET Drain Voltage ADC Readings

These registers store the drain voltages of the external

current sink FETs. For each register, bits 6–0 are the

conversion data of the ADC outputs. Bit 7 is used to

show if the conversion is terminated by the ADC (indi-

cated by 0) or if there is an internal timeout (indicated

by 1). If the drain voltage exceeds the preset reference

voltage, the corresponding LED string fault bit is assert-

ed. See the

Faults and Fault Detection

section for more

information on the internal timeout function.

Voltage ADC Output

Bits 6-0 of this register store the voltage present at

OVP. This voltage is a scaled down version of the

switching regulator output voltage. Bit 7 is not used.

This register stores all the external events or fault infor-

mation such as overvoltage and shorted LED string

faults. The fault events are logged only if the system is

not in standby mode and their active states are longer

than one clock cycle. Cycle enable or power to clear the

fault status register. Initiating standby mode using the

C interface can also be used to clear the fault status

Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

20 ______________________________________________________________________________________

Table 2. Register File Assignments

ADDRESS

R/W

USED BIT

RANGE

RESET

VALUE

DESCRIPTION

00h R/W [6:0] 00h LED String 1 current programming value.

01h R/W [6:0] 00h LED String 2 current programming value.

02h R/W [6:0] 00h LED String 3 current programming value.

03h R/W [6:0] 00h LED String 4 current programming value.

04h R/W [6:0] 00h Switching regulator output voltage programming value.

05h R [7:0] 00h LED String 1 external FET drain voltage ADC output.

06h R [7:0] 00h LED String 2 external FET drain voltage ADC output.

07h R [7:0] 00h LED String 3 external FET drain voltage ADC output.

08h R [7:0] 00h LED String 4 external FET drain voltage ADC output.

09h R [6:0] 00h OVP voltage, ADC output.

0Ah R [5:0] 00h Fault status register.

0Bh R/W [0] 00h Device standby command.

0Ch R [2:0] — Device revision code.

vate this mode using the I

C interface. Next, perform a

read operation on the fault status register. The old fault

information is reported in this first read operation. The

conclusion of the read operation clears the data con-

tained in the register. Subsequent read operations con-

firm that the fault status register has been cleared.

The description of this register is as follows:

Bit 0: Overvoltage sense flag. This flag is set if the volt-

age at OVP exceeds 1.25V; switching stops until power

or the enable or standby is cycled.

• Bit 1: Not used.

• Bit 2: LED string 1 shorted flag. A diode short in LED

string 1 has been detected if this bit is set.

• Bit 3: LED string 2 shorted flag. A diode short in LED

string 2 has been detected if this bit is set.

• Bit 4: LED string 3 shorted flag. A diode short in LED

string 3 has been detected if this bit is set.

• Bit 5: LED string 4 shorted flag. A diode short in LED

string 4 has been detected if this bit is set.

When register 0Bh bit 0 is set to 1, the IC enters a low-

current standby mode. In this mode, the system clock is

off and no operation is allowed. Set this bit to 0 to leave

standby mode and back to normal operation mode.

These 3 bits are a hardwired value that identifies the

IC’s revision.

Applications Information

Programming LED Currents

The MAX16826 uses sense resistors (R28, R29, R30,

R31 in the

Typical Application Circuit

) to set the output

current for each LED string. To set the LED current for a

particular string, connect a sense resistor across the

corresponding current-sense input (CS1–CS4) and

GND. For optimal accuracy, connect the low-side of the

current-sense resistors to GND with short traces. The

value needed for the sense resistor for a given current

is calculated with the equation below:

R31 = V

CS1

OUT1

where V

CS1

can be set from 97mV to 316mV by the

internal registers through the I

C interface and I

OUT1

the desired LED string 1 current.

Calculating the Value of Peak

Current-Limit Resistor

The value of R12 sets the peak switching current that

flows in the switching FET (Q1). Set the value of resistor

R12 using the equation below:

R12 = 0.19/(1.2 x I

)

where I

is the peak inductor current at minimum input

voltage and maximum load.

Boost Inductor Value

The value of the boost inductor is calculated using the

following equation:

where V

INMIN

is the minimum input voltage, V

OUT

is the

desired output voltage, and f

is the switching fre-

quency, and ΔI

is the peak-to-peak ripple in the boost

inductor. Higher inductor values lead to lower ripple but

at a higher cost and size. Choose an inductor value

that gives peak-to-peak ripple current in the order of

30% to 40% of the average current in the inductor at

low-line and full-rated load. This choice of inductor is a

compromise between cost, size, and performance for

the boost converter.

Setting Output Voltage

Set the switch regulator output voltage by connecting

FB to the center of a resistive voltage-divider between

the switching regulator output and GND. V

is regulat-

ed to a voltage from 0.88V to 1.25V (typ) set by an

internal register through the I

C interface. Choose R13

and R14 in the

Typical Application Circuit

for a reason-

able bias current in the resistive divider and use the fol-

lowing formula to set the output voltage:

OUT

= (1 + R13/R14) x V

where V

is the regulated voltage set by the internal

Adaptive Voltage Optimization

The availability of the digitized switching regulator output

voltage and current sink drain voltages and the ability to

change the switching regulator output voltage provide

the ability to do adaptive voltage optimization. A slow

digital control loop is established with an external μC

closing the loop. Firmware residing in the external μC is

tasked to read each one of the current sink FET drain

voltages and select the minimum value of the four LED

strings. The minimum value is subtracted from the scaled

output voltage reading, and then the switching regulator

output is forced to maintain the difference required to

provide current regulation in the current sink FETs.

V VV

V f I

INMIN OUT INMIN

OSWL

()

××

−

MAX16826

Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

______________________________________________________________________________________ 21

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P26

MAX16826ATJ+

Mfr. #:

Buy MAX16826ATJ+

Manufacturer:

Maxim Integrated

Description:

LED Lighting Drivers Prog 4-String HB

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

MAX16826ATJ+

MAX16826ATJ+

Products related to this Datasheet