On-board pass elements minimize the need for external

components while providing ±5% LED current accura-

cy. Additional features include a +5V (±5%) regulated

output with 4mA output current capability and thermal

protection.

The MAX16824/MAX16825 use a feedback loop to lin-

early control the current at each output. The voltage

across each sense resistor is regulated to 200mV by

the internal feedback loop. The output current is set by

+5V Regulator (REG)

The MAX16824/MAX16825 include a fixed +5V output

regulator that delivers up to 4mA of load current for

auxiliary low power applications throughout the 6.5V to

28V input voltage range. Connect a 1µF compensation

capacitor from REG to ground.

Thermal Protection

The MAX16824/MAX16825 enter a thermal shutdown

mode in the event of overheating. When the junction

protection circuit turns off the series pass elements.

The MAX16824/MAX16825 recover from thermal shut-

down mode when the junction temperature drops by

23°C. The thermal protection does not operate if the

regulator (REG) is in a short-circuit condition.

4-Wire Serial Interface (MAX16825)

The MAX16825 features a 4-wire serial interface (DIN,

CLK, LE, OE) and a data output (DOUT) that allows the

use of a microcontroller to write brightness data to the

MAX16825. The serial-interface data word length is 3

bits (D0, D1, D2). The functions of the interface inputs

are as follows: DIN is the serial-data input, which must

be stable when it is sampled by the MAX16825 on the

rising edge of CLK. Data shifts in with the MSB first.

This means that data bit D2 is clocked in first, followed

by 2 more data bits (D1 and finishing with the LSB D0).

CLK is the serial-clock input, which shifts data at DIN

into the MAX16825’s 3-bit shift register on the rising

edge. LE is the latch-enable input that allows the trans-

fer of data from the MAX16825’s 3-bit shift register to its

3-bit latch when LE is high (transparent latch) and

latches the data on the falling edge of LE (Figure 4).

Output enable (OE) provides simultaneous control of

the output drivers. Driving OE high places outputs

OUT1, OUT2, and OUT3 into a high-impedance mode

without altering the contents of the output latches.

Driving OE low allows outputs OUT1, OUT2, and OUT3

to follow the state of the output latches.

OE is independent of the operation of the serial inter-

face. Data can be shifted into the serial-interface shift

register and latched regardless of the state of OE.

DOUT is the serial-data output that shifts data out from

the MAX16825’s 3-bit shift register on the rising edge of

CLK. Data at DIN propagates through the shift register

and appears at DOUT three clock cycles later.

Applications Information

Programming the LED Current

The MAX16824/MAX16825 use sense resistors to set the

output current in each channel. To set the LED current

for a particular channel, connect a sense resistor across

the corresponding current-sense input (CS_) and GND.

For better performance, connect the low side of the cur-

rent-sense resistors to the IC’s ground terminal and the

high side to the CS_ terminal with short traces. The value

of the sense resistor for a given desired current is calcu-

lated with the following equation:

Electrical Characteristics table).

LED Supply Voltage Considerations

For proper operation, the minimum LED supply voltage

(applied between the LED string anode and ground)

must always be:

series connected LEDs and

dropout voltage of the regulator.

Pulse-Width Dimming (MAX16824)

The MAX16824 includes pulsed-width current dimming

inputs (PWM_) to control the LED brightness. An appli-

cation of up to 5kHz signal or less is recommended at

PWM_ input for proper operation. PWM_ also functions

as an active-high enable input for each output channel.

A logic-low at PWM_ turns off OUT_ and a logic-high

turns on OUT_.

Pulse-Width Dimming (MAX16825)

The MAX16825 provides three methods of pulsed-width

current dimming.

One method of pulse dimming the output channels is to

drive OE low while latching a different set of three bits

VV

V

V

LED MIN

CS

FT MAX

DO

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_

(

)

≥+

+ Δ

R

VV

IA

CS

CS

OUT

_

_

_

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Ω=

High-Voltage, Three-Channel Linear

High-Brightness LED Drivers

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