Undervoltage Lockout (UVLO)

The MAX16822A/MAX16822B include UVLO with

500mV hysteresis. The internal MOSFET turns off when

DIM Input

LED dimming is achieved by applying a PWM signal at

DIM. A logic level below 0.6V at DIM forces the

MAX16822A/MAX16822B’s output low, thus turning off

the LED current. To turn the LED current on, the logic

level at DIM must be greater than 2.8V.

Thermal Shutdown

The MAX16822A/MAX16822B thermal-shutdown fea-

ture turns off the LX driver when the junction tempera-

ture exceeds +165°C. The LX driver turns back on

when the junction temperature drops 10°C below the

shutdown-temperature threshold.

Analog Dimming

The MAX16822A/MAX16822B offer an analog dimming

feature that reduces the output current when the volt-

age at TEMP_I is below the internal 2V threshold volt-

age. The MAX16822A/MAX16822B achieve analog

dimming by either an external DC voltage source con-

nected between TEMP_I and ground or by a voltage on

a resistor connected across TEMP_I and ground

induced by an internal current source of 25µA. When

the voltage at TEMP_I is below the internal 2V threshold

limit, the MAX16822A/MAX16822B reduce the LED cur-

rent. Use the following formula to set the analog dim-

ming current.

from the

voltage at TEMP_I.

Thermal Foldback

The MAX16822A/MAX16822B also include a thermal-

foldback feature that reduces the output current when

the temperature of the LED string exceeds a specified

temperature point. These devices enter thermal-fold-

back mode when the voltage drop on the NTC thermis-

tor, thermally attached to the LEDs and electrically

connected between TEMP_I and ground, drops below

the internal 2V threshold limit.

Applications Information

The LED current is programmed with a current-sense

resistor connected between IN and CS. Use the equa-

tion below to calculate the value of this resistor:

Electrical Characteristics table for values).

Current-Regulator Operation

The MAX16822A/MAX16822B regulate the LED current

using a comparator with hysteresis (see Figure 2). As

the current through the inductor ramps up and the volt-

age across the sense resistor reaches the upper

threshold, the internal MOSFET turns off. The internal

MOSFET turns on again when the inductor current

ramps down through the freewheeling diode until the

voltage across the sense resistor equals the lower

threshold. Use the following equation to determine the

operating frequency:

voltage drop of 1 LED, and

Inductor Selection

The MAX16822A/MAX16822B operate up to a switching

frequency of 2MHz. For space-sensitive applications,

the high switching frequency allows the size of the

inductor to be reduced. Use the following formula to

calculate an approximate inductor value and use the

closest standard value:

For component selection, use the MAX16822A/B Design

L approx

VnV

nV

R

VV

f

IN

LED

LED

SENSE

IN

(.)

()

=

××

××

−

Δ

S

SW

f

VnV

nV

R

VV

L

SW

IN

LED

LED

SENSE

IN

=

××

××

−

()

Δ

R

VV

V

IA

SENSE

SNSHI

SNSLO

LED

()

()( )

()

Ω=

+

1

2

IA

I

A

FB

V

VV

TF

LED

SLOPE

TFB ON

A

()

()

_

=×

⎛

⎝⎜

⎞

⎠⎟

×

−−

1

1

D

D

V

()

⎡

⎣

⎢

⎤

⎦

⎥

()

2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

_______________________________________________________________________________________

7