MAX16805ATP+T Datasheet MAX16805ATP+T, MAX16806ATP+, MAX16806ATP+T | P10-P12

MAX16805/MAX16806

EEPROM-Programmable, High-Voltage, 350mA

LED Drivers with LED Current Foldback

10 ______________________________________________________________________________________

SDA

SCL

HD:STA

LOW

HIGH

HD:DAT

SU:DAT

REPEATED

START

SU:STA

HD:STA

SU:STO

STOP START

BUF

Figure 1. I

C Serial Interface Timing Diagram

Detailed Description

The MAX16805/MAX16806 are constant-current regu-

lators that provide up to 350mA of current to one or

more strings of high-brightness LEDs. A wide operat-

ing input voltage range of 5.5V to 40V makes the

devices ideal for automotive applications. The

MAX16805/MAX16806 feature the I

C interface that

allows communication with the internal dynamic regis-

ters and EEPROM.

Dynamic registers control the MAX16805/MAX16806

functions and can be updated in real time through the

C interface. See Table 2 for register addresses. Turning

off the input voltage clears the dynamic register contents.

To save settings, store them into the EEPROM. The

MAX16805/MAX16806 load the stored settings into the

dynamic registers at power-up. In addition, during nor-

mal operation a write command to the EEPROM Content

Transfer register loads the stored settings into the

dynamic register. Information stored can be transferred

into dynamic registers after issuing a “write” command to

the EEPROM Content Transfer register.

The MAX16805/MAX16806’s 5V regulator (V5) provides

up to 2mA of current to external circuitry. However, the

MAX16806’s 5V regulator can deliver 2mA of output cur-

rent only when the momentary switch is not used. When

the momentary switch is active, the MAX16806 achieves

up to 0.5mA of current. In addition, the

MAX16805/MAX16806 feature thermal and output short-

circuit protection. The wide operating voltage range

helps protect the device against large transients up to

45V such as those found in load dump situations.

The MAX16805/MAX16806 use a feedback loop to

control the output current. The differential voltage

across the sense resistor is compared to a fixed refer-

ence voltage and the error is amplified to serve as the

drive to the internal pass device, see the

Functional

Diagram

. The MAX16805/MAX16806 offer a program-

mable LED current reference using the Binning

Adjustment register.

These devices are current controllers internally opti-

mized for driving the impedance range expected from

1 to 10 (or more) high-brightness LEDs.

Dimming Input (DIM)

The MAX16805/MAX16806’s dimming input operates

with either an analog or PWM control signal. If the

pulse detector detects three edges of a PWM signal

with a frequency range between 80Hz to 2kHz, the

MAX16805/MAX16806 synchronize to external PWM

input signal and pulse-width-modulate the LED current.

If an analog control signal is applied to DIM, the

MAX16805/MAX16806 compare the DC input to an

internally generated 200Hz ramp to pulse-width-modu-

late the LED current. The maximum peak value of the

200Hz ramp can be programmed using the Ramp

Peak register. This allows the LED current to be adjust-

ed through the I

C interface from 50% (typ) to 100% in

real time when V

DIM

is 1.54V.

The output current duty cycle is adjustable from 0% to

100% (0.21V < V

DIM

< 3.1V).

Use the following formula to calculate the output cur-

rent duty cycle:

Duty cycle = (V

DIM

- 0.21V) / V

RAMP

MAX16805/MAX16806

EEPROM-Programmable, High-Voltage, 350mA

LED Drivers with LED Current Foldback

______________________________________________________________________________________ 11

The dimming feature can be used for LED brightness

adjustment (see the

Typical Operating Circuits

) and

theater dimming. If the external PWM signal is used,

theater dimming can be achieved by varying the PWM

duty cycle. Figure 2 shows a simple circuit that imple-

ments theater dimming with a DC input signal.

Thermal Sensor Inputs/I

C Interface

(TFP/SCL and TFN/SDA)

The MAX16806 features dual-function inputs, TFP/SCL

and TFN/SDA. In programming mode, TFP/SCL and

TFN/SDA serve as the I

C serial communication inter-

face. TFP/SCL and TFN/SDA also serve as inputs for

analog signals generated by an external temperature

sensor such as the MAX6613. When the thermal sensor

is not used, connect TFP/SCL and TFN/SDA through

50kΩ resistors to V5 and GND, respectively.

The MAX16805 does not offer dual-function inputs. SCL

and SDA are used only to communicate with the

MAX16805 through the I

C interface.

Momentary Switch Interface (SW)

The MAX16806 offers a momentary switch (SW) that

overrides the analog dimming signal by latching the

output current to 100% duty cycle. The MAX16806

does not override external PWM signal at DIM or dim-

ming caused by thermal or LED current foldback. To

latch the output current into a 100% duty cycle, press

SW once. To restore the initial duty cycle determined

by the DC level at DIM, press SW again. The

MAX16806 provides a minimum of 1mA of wetting cur-

rent to the momentary switch.

Overtemperature Protection

The MAX16805/MAX16806 enter a thermal shutdown in

the event of overheating. This typically occurs in over-

load or output short-circuit conditions. When the junc-

tion temperature exceeds T

= +155°C (typ), the

internal thermal protection circuitry turns off the pass

device. The MAX16805/MAX16806 recover from ther-

mal shutdown once the junction temperature drops by

+23°C (typ). This feature allows self-protection by ther-

mally cycling in the event of a short-circuit or overload

condition.

Digital Interface

The MAX16805/MAX16806 feature an I

C, 2-wire serial

interface consisting of a bidirectional serial data line

(SDA) and a serial clock line (SCL). SDA and SCL facili-

tate bidirectional communication between the

MAX16805/MAX16806 and the master device at rates

up to 400kHz. The master (typically a microcontroller)

initiates data transfer on the bus and generates SCL.

Start and Stop Conditions

Both SCL and SDA remain high when the interface is

not busy. A master controller signals the beginning of a

transmission with a START condition by transitioning

SDA from high to low while SCL is high. The master

controller issues a STOP condition by transitioning the

SDA from low to high while SCL is high, when it finishes

communicating with the slave. The bus is then free for

another transmission (Figure 3).

MAX16805

MAX16806

OUT

LEDs

SENSE

THEATER

DIMMING

SIGNAL

+5V REG

CS+

0.1μF

CS-

DIM

GND

Figure 2. Theater Dimming Light

START

CONDITION

SDA

SCL

STOP

CONDITION

Figure 3. I

C Communication Start and Stop Conditions

MAX16805/MAX16806

EEPROM-Programmable, High-Voltage, 350mA

LED Drivers with LED Current Foldback

12 ______________________________________________________________________________________

Bit Transfer

One data bit is transferred during each clock pulse.

The data on the SDA line must remain stable while SCL

is high (Figure 4).

Acknowledge

The acknowledge bit is a clocked 9th bit that the recipi-

ent uses to handshake receipt each byte of data

(Figure 5). Therefore, each byte effectively transferred

requires 9 bits. The master controller generates the 9th

clock pulse, and the recipient pulls down SDA during

the acknowledge clock pulse, so the SDA line remains

stable low during the high period of the clock pulse.

Slave Address

The MAX16805/MAX16806 have a 7-bit-long slave

address (Figure 6, Table 1). The 8th bit following the 7-

bit slave address is the R/W bit. Set the R/W bit low for

a write command and high for a read command.

DATA STABLE,

DATA VALID

SDA

SCL

CHANGE OF DATA

ALLOWED

WRITE ADDRESS (HEX) READ ADDRESS (HEX)

0xEE 0xEF

Figure 4. Bit Transfer

SDA

START MSB

SCL

456

A7 A6

A4 A3 A2

A1 RW ACK

Figure 6. Slave Address

SDA

START

SCL

NOT ACKNOWLEDGE

ACKNOWLEDGE

Figure 5. Acknowledge

Table 1. Slave Address

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P19

MAX16805ATP+T

Mfr. #:

Buy MAX16805ATP+T

Manufacturer:

Maxim Integrated

Description:

LED Lighting Drivers EEPROM-Prog 350mA w/Current Foldback

Lifecycle:

New from this manufacturer.

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MAX16805ATP+T

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