Rainbow Electronics MAX16822B User Manual

General Description

The MAX16822A/MAX16822B step-down constant-cur­rent high-brightness LED (HB LED) drivers provide a
cost-effective design solution for automotive
interior/exterior lighting, architectural and ambient light­ing, LED bulbs, and other LED illumination applications.

The MAX16822A/MAX16822B operate from a +6.5V to
+65V input-voltage range. A high-side current-sense
resistor adjusts the output current up to 350mA and a
dedicated pulse-width modulation (PWM) input enables
pulsed LED dimming over a wide range of brightness
levels.

These devices are well suited for applications requiring
a wide input-voltage range. The high-side current sens­ing and an integrated current-setting circuitry minimize
the number of external components while delivering an
average output current with ±3% accuracy. A hysteretic
control method ensures excellent input supply rejection
and fast response during load transients and PWM dim­ming. The MAX16822A allows 10% current ripple and
the MAX16822B allows 30% current ripple. Both
devices operate up to a switching frequency of 2MHz,
thus allowing the use of small-sized components.

The MAX16822A/MAX16822B offer an analog dimming
feature that reduces the output current by applying an
external DC voltage below the internal 2V threshold volt­age from TEMP_I to GND. TEMP_I also sources 25µA to
a negative temperature coefficient (NTC) thermistor con­nected between TEMP_I and GND, thus providing an
analog thermal-foldback feature that reduces the LED
current when the temperature of the LED string exceeds
a specified temperature point.

An additional feature includes thermal-shutdown pro­tection that turns off the LX driver when the junction
temperature exceeds +165°C.

The MAX16822A/MAX16822B operate over the -40°C to
+125°C automotive temperature range and are available
in an 8-pin SO package.

Applications

Architectural, Industrial, and Ambient Lighting

Automotive RCL, DRL, and Fog Lights

Heads-Up Displays

Indicator and Emergency Lighting

Features

♦ High-Efficiency Solution

♦ 6.5V to 65V Input-Voltage Range

♦ On-Board 65V, 0.85Ω Power MOSFET

♦ Hysteretic Control: Up to 2MHz Switching

Frequency

♦ ±3% LED Current Accuracy

♦ 200mV Current-Sense Reference

♦ Resistor-Programmable Constant LED Current

♦ Integrated High-Side Current Sense

♦ Thermal-Foldback Protection/Linear Dimming

♦ Thermal-Shutdown Protection

♦ Available in an 8-Pin SO Package

♦ -40°C to +125°C Operating Temperature Range

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

________________________________________________________________

Maxim Integrated Products

1

Ordering Information

LX

LXPGND

1

2

8

7

TEMP_I

DIMIN

GND

CS

3

4

6

5

MAX16822A
MAX16822B

L1

C2

ON

OFF

D1

HB LEDs

NTC

*

*

OPTIONAL

R

SENSE

V

IN

C1

Typical Application Circuit

19-4141; Rev 1; 6/08

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

+

Denotes a lead-free/RoHS-compliant package.

PART TEMP RANGE

PIN-PACKAGE

-40°C to +125°C 8 SO

-40°C to +125°C 8 SO

Pin Configuration appears at end of data sheet.

MAX16822AASA+

MAX16822BASA+

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with
Integrated MOSFET and High-Side Current Sense

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= +24V, V

DIM

= VIN, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer board. For detailed information on package thermal considerations, see www.maxim-ic.com/thermal-tutorial

.

IN, CS, LX, DIM to GND .........................................-0.3V to +70V

TEMP_I to GND .......................................................-0.3V to +6V

PGND to GND ......................................................-0.3V to +0.3V

CS to IN .................................................................-0.3V to +0.3V

Maximum Current into Any Pin

(except IN, LX, and PGND).............................................20mA

Continuous Power Dissipation (T

A

= +70°C)

8-Pin SO (derate 7.4mW/°C above +70°C)...............588.2mW

Junction-to-Ambient Thermal Resistance (θ

JA

) (Note 1) ...136°C/W

Pin-to-Pin ESD Ratings......................................................±2.5kV

Operating Temperature Range .........................-40°C to +125°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

Input-Voltage Range V

Ground Current No switching 1.5 mA

Supply Current V

UNDERVOLTAGE LOCKOUT (UVLO)

Undervoltage Lockout UVLO

Undervoltage-Lockout Hysteresis 0.5 V

SENSE COMPARATOR

Sense Voltage Threshold High V

Sense Voltage Threshold Low V

Propagation Delay to Output High t

Propagation Delay to Output Low t

CS Input Current I

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IN

SNSHI

SNSLO

DPDH

DPDL

CSIN

< 0.6V, VIN = 12V 350 µA

DIM

VCS = VIN - 100mV, VIN rising from 4V until
V

< 0.5V

LX

V

CS

until V

MAX16822A, (VIN - VCS) rising from
140mV until V

MAX16822B, VIN - VCS rising from 140mV
until V

MAX16822A, VIN - VCS falling from 260mV
until V

MAX16822B, VIN - VCS falling from 260mV
until V

Falling edge of VIN - VCS from 140mV to
260mV to V

Rising edge of VCS - VIN from 260mV to
140mV to V

VIN - VCS = 200mV 3.5 µA

IN

= VIN - 100mV, VIN falling from 6.5V

> 0.5V

LX

LX

LX

LX

> 0.5V

< 0.5V

< 0.5V

LX

LX

IN

> 0.5V

LX

IN

IN

IN

= 0.5V

< 0.5V

IN

IN

IN

6.5 65 V

201 210 216

218 230 236

185 190 198

166 170 180

6.25 6.5

6

50 ns

50 ns

V

mV

mV

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= +24V, V

DIM

= VIN, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.)

EFFICIENCY

vs. V

IN

MAX16822A toc01

VIN (V)

EFFICIENCY (%)

5545352515

75

80

85

90

95

100

70

565

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

9 LEDs

DUTY CYCLE

vs. V

IN

MAX16822A toc02

VIN (V)

DUTY CYCLE (%)

5545352515

10

20

30

40

50

60

70

80

90

100

0

565

1 LED

3 LEDs

5 LEDs

7 LEDs

15 LEDs

11 LEDs

13 LEDs

FREQUENCY

vs. V

IN

MAX16822A toc03

VIN (V)

FREQUENCY (kHz)

5545352515

10

20

30

40

50

60

70

80

90

100

0

565

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

Typical Operating Characteristics

(VIN= V

DIM

= 48V, C

VCC

= 1µF, R

SENSE

= 0.62Ω, L = 220µH (connected between IN and CS). Typical values are at TA= +25°C,

unless otherwise noted.)

INTERNAL MOSFET

Drain-to-Source Resistance R

LX Leakage Current I

DIM INPUT

DIM Input-Voltage High V

DIM Input-Voltage Low V

DIM Turn-On Time t

DIM Input Leakage High V

DIM Input Leakage Low V

THERMAL SHUTDOWN

Thermal-Shutdown Threshold Temperature rising 165

Thermal-Shutdown Threshold
Hsysteresis

THERMAL FOLDBACK

Thermal-Foldback Enable
Threshold Voltage

Thermal-Foldback Slope FB

TEMP_I Output Bias Current I

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VIN = V
I

DSON

VIN = V
I

LX_LEAK

IH

IL

DIM_ON

V

TFBON_THRVDIM

SLOPEVDIM

TEMP_I

V

VIN - VCS = 100mV 2.8 V

VCS - VIN = 100mV 0.6 V

V

= 350mA

LX

= 350mA

LX

DIM

DIM

DIM

DIM

= 24V, VCS = 23.9V,

DIM

= 6.0V, VCS = 5.9V,

DIM

= 0V, VLX = 65V 10 µA

rising edge to VLX < 0.5V

= V

IN

IN

= 0V -3 0 µA

= 5V 1.9 2.0 2.12 V

= 5V 0.75 1/V

25 26.5 28 µA

0.85 1.7

12

200 ns

15 µA

10

Ω

o

C

o

C

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with
Integrated MOSFET and High-Side Current Sense

4 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VIN= V

DIM

= 48V, C

VCC

= 1µF, R

SENSE

= 0.62Ω, L = 220µH (connected between IN and CS). Typical values are at TA= +25°C,

unless otherwise noted.)

LED CURRENT

vs. V

TEMP_I

MAX16822A toc09

V

TEMP_I

(V)

LED CURRENT (mA)

2.42.01.2 1.60.80.4

50

100

150

200

250

300

350

400

450

500

0

0 2.8

I

LED

vs. TEMPERATURE

MAX16822A toc10

TEMPERATURE (°C)

I

LED

(A)

1109580655035205-10-25

0.1

0.2

0.3

0.4

0.5

0

-40 125

VIN = 48V

PWM DIMMING

AT 200Hz DUTY CYCLE (90%)

MAX16822A toc07

1ms/div

I

LED

200mA/div

V

DIM

5V/div

V

IN

= 48V

8 LEDs

0

0

PWM DIMMING

AT 20kHz DUTY CYCLE (90%)

MAX16822A toc08

10μs/div

I

LED

200mA/div

V

DIM

5V/div

0

0

NORMALIZED ILED

0.950

1.10

1.05

5 LEDs 7 LEDs

1.00

0.90

3 LEDs

1 LED

065

NORMALIZED I

vs. V

IN

9 LEDs

11 LEDs

VIN (V)

LED

13 LEDs

QUIESCENT CURRENT

500

450

400

MAX16822A toc04

350

15 LEDs

60555045403530252015105

300

250

200

150

QUIESCENT CURRENT (μA)

100

50

0

065

vs. V

VIN (V)

PWM DIMMING

IN

MAX16822A toc05

V

= 0V

DIM

605545 5015 20 25 30 35 405 10

AT 200Hz DUTY CYCLE (10%)

1ms/div

MAX16822A toc06

V

IN

8 LEDs

= 48V

I

LED

200mA/div

0

V

DIM

5V/div
0

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

_______________________________________________________________________________________

5

Typical Operating Characteristics (continued)

(VIN= V

DIM

= 48V, C

VCC

= 1µF, R

SENSE

= 0.62Ω, L = 220µH (connected between IN and CS). Typical values are at TA= +25°C,

unless otherwise noted.)

LX

RDSON

vs. TEMPERATURE

MAX16822A toc11

TEMPERATURE (°C)

LX

RDSON

(Ω)

1109580655035205-10-25

0.5

0.6

0.7

0.8

0.9

1.0

0.4

-40 125

VIN = 6.5V

VIN = 65V

VIN = 48V

I

TEMP_I

vs. TEMPERATURE

MAX16822A toc12

I

TEMP_

(μA)

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

30.0

25.0

TEMPERATURE (°C)

1109580655035205-10-25-40 125

VIN = 48V

Pin Description

Detailed Description

The MAX16822A/MAX16822B are step-down, constant­current, high-brightness LED (HB LED) drivers. These
devices operate from a +6.5V to +65V input-voltage
range and deliver up to 350mA of output current. A high­side current-sense resistor sets the output current and a

dedicated PWM dimming input enables pulsed LED
dimming over a wide range of brightness levels.

A high-side current-sensing scheme and an on-board
current-setting circuitry minimize the number of exter­nal components while delivering LED current with ±3%
accuracy, using a 1% sense resistor. See Figure 1 for
an internal block diagram.

PIN NAME FUNCTION

1 CS Current-Sense Input. Connect a resistor between IN and CS to program the LED current.

2 IN Positive Supply Voltage Input. Bypass with a 1µF or higher value capacitor to GND.

3 GND Ground

4 PGND Power Ground

5, 6 LX Switching Node

7 DIM

8 TEMP_I

Logic-Level Dimming Input. Drive DIM low to turn off the current regulator. Drive DIM high to
enable the current regulator.

Thermal Foldback Control and Linear Input. Bypass with a 0.01µF capacitor to GND if thermal
foldback or analog dimming is used. See the Thermal Foldback section for more details.

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with
Integrated MOSFET and High-Side Current Sense

6 _______________________________________________________________________________________

Figure 1. Internal Block Diagram

IN

I

SET

V

_ANA

CC

CS

BANDGAP

REFERENCE

1.23V

V

REGULATOR

CC

CURRENT-SENSE
COMPARATOR

UVLO
COMPARATOR

V

CC

PWM
DIMMING

GATE

DRIVER

MAX16822B

LX

0.85Ω, 65V
DMOS SWITCH

_ANA

MAX16822A

DIM

TEMP_I

DIM

BUFFER

V

FTBON_THR

V

_ANA

CC

25μA

THERMAL
FOLDBACK

2V

GND

COMPARATOR

PGND

Undervoltage Lockout (UVLO)

The MAX16822A/MAX16822B include UVLO with
500mV hysteresis. The internal MOSFET turns off when
V

IN

falls below 5.5V to 6.0V.

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 fea­ture turns off the LX driver when the junction tempera­ture 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 volt­age at TEMP_I is below the internal 2V threshold volt­age. The MAX16822A/MAX16822B achieve analog
dimming by either an external DC voltage source con­nected 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 cur­rent. Use the following formula to set the analog dim­ming current.

where V

TFB_ON

= 2V and FB

SLOPE

= 0.75 are obtained

from the

Electrical Characteristics

table and VADis the

voltage at TEMP_I.

Thermal Foldback

The MAX16822A/MAX16822B also include a thermal­foldback feature that reduces the output current when
the temperature of the LED string exceeds a specified
temperature point. These devices enter thermal-fold­back mode when the voltage drop on the NTC thermis­tor, thermally attached to the LEDs and electrically
connected between TEMP_I and ground, drops below
the internal 2V threshold limit.

Applications Information

Selecting R

SENSE

to Set LED Current

The LED current is programmed with a current-sense
resistor connected between IN and CS. Use the equa­tion below to calculate the value of this resistor:

where V

SNSHI

is the sense voltage threshold high and

V

SNSLO

is sense voltage threshold low (see the

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 volt­age 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:

where n is the number of LEDs, V

LED

is the forward

voltage drop of 1 LED, and ΔV = (V

SNSHI

- V

SNSLO

).

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
Tool available at:www.maximic.com/MAX16822-

software.

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

_______________________________________________________________________________________ 7

IAI A FB

() () ()

=×

TF LED SLOPE TFB ON AD

⎡

−−1

⎢
⎣

1

⎛

⎞

VVV

×

⎜

⎟

()

⎝

⎠

V

_

R

SENSE

()

Ω=

2

−()

VnV nV R

f

SW

⎤
⎥
⎦

L approx

(.)

IN LED LED SENSE

=

−

VnV nV R

()

IN LED LED SENSE

=

VVV

()()

VVL

+1

SNSHI SNSLO

IA

()

LED

××

Δ

××

IN

××

Δ

VVf

××

IN SW

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with
Integrated MOSFET and High-Side Current Sense

8 _______________________________________________________________________________________

Freewheeling-Diode Selection

For stability and best efficiency, a low forward-voltage
drop diode with fast reverse-recovery time and low
capacitance is recommended. A Schottky diode is a
good choice as long as its breakdown voltage is high
enough to withstand the maximum operating voltage.

PCB Layout Guidelines

Careful PCB layout is critical to achieve low switching
losses and stable operation. Use a multilayer board
whenever possible for better noise immunity. Minimize
ground noise by connecting high-current ground
returns, the input bypass-capacitor ground lead, and

the output-filter ground lead to a single point (star
ground configuration). In normal operation, there are two
power loops. One is formed when the internal MOSFET
is on and the high current flows through IN, R

SENSE

,
LED load, the inductor, the internal MOSFET, and GND.
The other loop is formed when the internal MOSFET is
off and the high-current circulates through R

SENSE

, LED
load, the inductor, and the freewheeling diode. Minimize
each loop area to reduce noise interaction.

Place R

SENSE

as close as possible to CS and IN. For
better noise immunity, a Kelvin connection between CS
and R

SENSE

is strongly recommended.

Figure 2. Current-Regulator Operation

HYSTERETIC

MODE

f

I

LED

AVG. LED

CURRENT

V

DIM

SW

ΔI

t

t1

tt2

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with

Integrated MOSFET and High-Side Current Sense

_______________________________________________________________________________________ 9

Chip Information

PROCESS: BiCMOS

Package Information

For the latest package outline information, go to

www.maxim-ic.com/packages

.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

8 SO S8-2

21-0041

LX

LXPGND

1

2

8

+

7

TEMP_I

DIMIN

GND

CS

SO

TOP VIEW

3

4

6

5

MAX16822A
MAX16822B

Pin Configuration

MAX16822A/MAX16822B

2MHz, High-Brightness LED Drivers with
Integrated MOSFET and High-Side Current Sense

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

10

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

Revision History

REVISION

NUMBER

0 5/08 Initial release —

1 6/08 Updated Ordering Information table to release MAX16822B. 1

REVISION

DATE

DESCRIPTION

PAGES

CHANGED