MAX16826ATJ+ Datasheet MAX16826ATJ+T, MAX16826ATJ+, MAX16826BATJ/V+ | P16-P18

MAX16826

is 2μs, so the ADC requires at least 5 of these minimum

pulses within the 190ms measurement window to com-

plete a conversion. During PWM dimming, LED current

pulse widths of less than 2μs are possible, but the ADC

may not have enough sampling time to complete a con-

version in this scenario and the corresponding data may

be incomplete or inaccurate. Therefore, adaptive volt-

age optimization may not be possible when the LED

current-pulse duration is less than 2μs. The LED current

pulse duration is shorter than the pulse applied at the

DIM_ inputs because of the LED turn-on delay.

Faults and Fault Detection

The MAX16826 features circuitry that automatically

detects faults such as overvoltage or shorted LED string.

An internal fault register at the address OAh is used to

record these faults. For example, if a shorted LED string

is detected, the corresponding fault register bit is set and

the faulty output is shut down.

Shorted LED strings are detected with fast comparators

connected to DR1–DR4. The trip threshold of these

comparators is 1.52V (typ). When this threshold is

exceeded, the shorted string is latched off and the cor-

responding bit of register OAh is set.

After the internal ADC completes a conversion, the

result is stored in the corresponding register and can

be read out by the external μC. The μC then compares

the conversion data with the preset limit to determine if

there is a fault.

When an LED string opens, the voltage at the corre-

sponding current-sink FET drain node goes to 0V.

However, the ADC can only complete a conversion if

the LED current comes into regulation. If an LED string

opens before the LED current can come into regulation,

the ADC cannot complete a conversion and the MSB

(eighth bit) is set to indicate an incomplete conversion

or timeout condition. Thus, an examination of the MSB

provides an indication that the LED string is open. If the

LED string opens after the LED current is in regulation,

the ADC can make conversions and reports that the

drain voltage is 0V. Therefore, to detect an open condi-

tion, monitor the MSB and the ADC measurement. If the

MSB is set and the CS_ on-time is greater than 2μs, or

if the ADC measures 0 at the drain, then there is an

open circuit.

Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

16 ______________________________________________________________________________________

Table 1. ADC Response

CONDITION ADC RESPONSE

Shorted string fault

Load full-scale code into register, no conversions on affected channel until power or enable is

cycled.

Shorted string fault while

converting

Immediately load full-scale code into register and cease conversion effort on this channel until

power or enable is cycled.

ADC register read when it is

being updated

Previous sample is shifted out through the I

C interface and then the register is updated with the

new measurement.

UVLO Immediately terminate conversions, do not update current register.

STBY Immediately terminate conversions, do not update current register.

SHDN Immediately terminate conversions, do not update current register.

FILE UNIT

ADC DAC

POWER

MANAGEMENT

OVP

SYSTEM

CLOCK

EXTERNAL

EVENTS

Figure 3. Digital Block Diagram

Overview of the Digital Section

Figure 3 shows the block diagram of the digital section in

the MAX16826. The I

C serial interface provides flexible

control of the IC and is in charge of writing/reading

to/from the register file unit. The ADC block is a 7-bit

5-channel SAR ADC. The eighth bit of the ADC data reg-

ister indicates an incomplete conversion or timeout has

occurred. This bit is set whenever the LED current fails to

come into regulation during the DIM PWM on-time. This

indicates there is either an LED open condition or the

CS_ on-time is less than 2μs.

A reason for this among other possibilities is an open

LED string condition. This eighth or MSB bit can be

tested to determine open string faults.

C Interface

The MAX16826 internal I

C serial interface provides

flexible control of the amplitude of the LED current in

each string and the switch-mode regulator output volt-

age. It is also able to read the current sink FET drain

voltages, as well as the switching regulator output volt-

age through OVP and thus enable some fault detection

and power dissipation minimization. By using an exter-

nal μC, the MAX16826 internal control and status regis-

ters are also accessed through the standard

bidirectional, 2-wire, I

C serial interface.

The I

C interface provides the following I/O functions

and programmability:

• Current sink FET drain and switching regulator out-

put-voltage measurement. The measurement for

each channel and the regulator output is stored in

its respective register and can be accessed

through the I

C interface. The SAR ADC measures

the drain voltage of each current sink FET sequen-

tially. This uses one 8-bit register for each channel

to store the measurement made by the 7-bit SAR

ADC and 1 bit to indicate a timeout during the ADC

conversion cycle.

• Adjustment of the switching regulator output. This is

used for adaptive voltage optimization to improve

overall efficiency. The switching regulator output is

downward adjustable by changing its reference

voltage. This uses a 7-bit register.

• Adjustment of the reference voltage of the current-

sink regulators. The reference voltage at the nonin-

verting input of each of the linear regulator drive

amplifiers can be changed to make adjustments in

the current of each LED string for a given sense

resistor. The output can be adjusted down from a

maximum of 316mV to 97mV in 1.72mV increments.

• Fault reporting. When a shorted string fault or an

overvoltage fault occurs, the fault is recorded.

• Standby mode. When a one is entered into the

standby register the IC goes into standby mode.

The 7-bit I

C address is 58h and the 8-bit I

C address

is B1h for a read operation and B0h for a write opera-

tion. Address the MAX16826 using the I

C interface to

read the state of the registers or to write to the registers.

Upon a read command, the MAX16826 transmits the

data in the register that the address register is pointing

to. This is done so that the user has the ability to confirm

the data written to a register before the output is

enabled. Use the fault register to diagnose any faults.

Serial Addressing

The I

C interface consists of a serial data line (SDA)

and a serial clock line (SCL) to achieve bidirectional

communication between the master and the slave. The

MAX16826 is a slave-only device, relying upon a mas-

ter to generate a clock signal. The master initiates data

transfer to and from the MAX16826 and generates SCL

to synchronize the data transfer (Figure 4).

MAX16826

Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

______________________________________________________________________________________ 17

SCL

SDA

BUF

START

CONDITION

STOP

CONDITION

REPEATED START CONDITION

START CONDITION

SU,STO

HD,STA

SU,STA

HD,DAT

SU,DAT

LOW

HIGH

HD,STA

Figure 4. 2-Wire Serial Interface Timing Detail

MAX16826

C is an open-drain bus. Both SDA and SCL are bidi-

rectional lines, connected to a positive supply voltage

using a pullup resistor. They both have Schmitt triggers

and filter circuits to suppress noise spikes on the bus to

ensure proper device operation.

A bus master initiates communication with the

MAX16826 as a slave device by issuing a START con-

dition followed by the MAX16826 address. The

MAX16826 address byte consists of 7 address bits and

a read/write bit (R/W). After receiving the proper

address, the MAX16826 issues an acknowledge bit by

pulling SDA low during the ninth clock cycle.

START and STOP Conditions

Both SCL and SDA remain high when the bus is not

busy. The master signals the beginning of a transmis-

sion with a START (S) condition by transitioning SDA

from high to low while SCL is high. When the master

has finished communicating with the MAX16826, it

issues a STOP (P) condition by transitioning SDA from

low to high while SCL is high. The bus is then free for

another transmission (Figure 4). Both START and STOP

conditions are generated by the bus master.

Bit Transfer

Each data bit, from the most significant bit to the least

significant bit, is transferred one by one during each

clock cycle. During data transfer, the SDA signal is

allowed to change only during the low period of the

SCL clock and it must remain stable during the high

period of the SCL clock (Figure 5).

Acknowledge

The acknowledge bit is used by the recipient to hand-

shake the receipt of each byte of data (Figure 6). After

data transfer, the master generates the acknowledge

clock pulse and the recipient pulls down the SDA line

during this acknowledge clock pulse, such that the

SDA line stays low during the high duration of the clock

pulse. When the master transmits the data to the

MAX16826, it releases the SDA line and the MAX16826

takes the control of SDA line and generates the

acknowledge bit. When SDA remains high during this

9th clock pulse, this is defined as the not acknowledge

signal. The master then generates either a STOP condi-

tion to abort the transfer, or a repeated START condi-

tion to start a new transfer.

Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

18 ______________________________________________________________________________________

START

CONDITION

(S)

DATA LINE STABLE

DATA VALID

DATA ALLOWED

TO CHANGE

STOP

CONDITION

(P)

SCL

SDA

Figure 5. Bit Transfer

SCL

SDA

BY MASTER

289

START CONDITION CLOCK PULSE FOR ACKNOWLEDGMENT

SDA

BY SLAVE

Figure 6. Acknowledge

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