MAX16821BEVKIT+ - Maxim Integrated Products, Inc.

General Description

The MAX16821B evaluation kit (EV kit) is a fully assem-

bled and tested surface-mount printed-circuit board

(PCB) designed to evaluate the MAX16821B pulse-

width-modulation (PWM) LED driver controller in a

boost configuration.

The MAX16821B EV kit operates from a DC supply volt-

age of 7V to 24V. The EV kit’s output is configured to

deliver 660mA of current into series LED string with a

maximum forward voltage of 28V. The LED brightness

can be dimmed using a digital PWM signal.

The EV kit provides an option to configure the

MAX16821B IC’s overvoltage protection, switching fre-

quency, and frequency compensation. The MAX16821B

EV kit also features a clock output PCB pad to drive a

second LED current regulator out-of-phase.

Features

♦7V to 24V Input-Voltage Range

♦660mA Output Current

♦Pulse-Width-Modulated LED Current Dimming

♦Resistor-Adjustable Overvoltage Protection and

Switching Frequency

♦Clock Output

♦Fully Assembled and Tested

Evaluates: MAX16821B

MAX16821B Evaluation Kit

________________________________________________________________

Maxim Integrated Products

19-1967; Rev 0; 11/07

Component List

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.

Ordering Information

PART TYPE

MAX16821BEVKIT+ EV Kit

Denotes lead-free and RoHS-compliant.

DESIGNATION QTY DESCRIPTION

C1, C5, C6 3

10µF±10%, 50V X7S ceramic

capacitors (1210)

Taiyo Yuden UMK325BJHI06K

C2 1

0.1µF±10%, 50V X7R ceramic

capacitor (1206)

Murata GRM319R71H104K

C3, C4 2

1000pF±10%, 25V X7R ceramic

capacitors (0603)

Murata GRM188R71E102K

C7 1

0.022µF±10%, 50V X7R ceramic

capacitor (0603)

Murata GRM188R71H223K

C8 1

4.7µF±10%, 6.3V X7R ceramic

capacitor (0603)

Murata GRM188R70J475K

C9, C10 2

0.1µF±10%, 50V X7R ceramic

capacitors (0603)

Murata GRM188R71H104K

D1 1 3A, 60V Schottky diode (SMA)

Diodes Inc. B360A-13-F

DESIGNATION QTY DESCRIPTION

L1 1 8.8µH, 4A inductor

Sumida CDEP105-8R8

N1–N4 4

60V, 115mA n-channel MOSFETs

(SOT23)

Central Semiconductor 2N7002

LEAD-FREE

N5 1

40V, 4.9A n-channel MOSFET

(8-pin SO)

Vishay Si4446DY

N6 1

60V, 3.2A n-channel MOSFET

(6-pin TSOP)

Vishay Si3458DV-E3

R1 1 249kΩ ±1% resistor (0603)

R2, R5, R10 3 10kΩ ±1% resistors (0603)

R3 0 Not installed, resistor—shorted

(0603)

R4 1 124kΩ ±1% resistor (0603)

R6 1

0.007Ω ±2%, 0.5W sense resistor

(1206)

IRC LRC-LRF1206LF-01-R007-G

Quick Start

Recommended Equipment

Before beginning, the following equipment is needed:

•7V to 24V, 4A DC power supply

•One series-connected LED string rated at 660mA

(28V maximum LED voltage)

•One current probe to measure LED current

•One voltmeter

Procedure

The MAX16821B EV kit is fully assembled and tested.

Follow the steps below to verify board operation.

Caution: Do not turn on the power supply until all

connections are completed.

1) Connect the positive terminal of the power supply to

the VIN pad on the EV kit. Connect the negative ter-

minal of the power supply to the PGND pad next to

the VIN pad.

2) Connect the anode end of the LED string to the

LED+ pad.

3) Connect the cathode end of the LED string to the

LED- pad.

4) Clip the current probe across the string wires to

measure the LED current.

5) Turn on the power supply and increase the voltage

to 7V or above.

6) Verify that the LED string DC current is approxi-

mately 660mA.

7) Measure the voltage between the LED+ to LED-

PCB pads.

Detailed Description

The MAX16821B EV kit circuit is designed to evaluate

the MAX16821B PWM LED driver controller. The EV kit

is configured in a boost topology and provides 660mA

LED current for a string of user-supplied external high-

brightness LEDs (HBLEDs) rated up to 28V. The

MAX16821B EV kit operates from a DC supply voltage

of 7V to 28V.

The EV kit average input current is set to 3.75A using

resistor R6. The LED current is set to 660mA using resis-

tor R7. A PWMDIM PCB pad is provided for PWM dim-

ming operation of the external LEDs. A CLKOUT PCB

pad is also available to drive a second LED current regu-

lator 180° out-of-phase with the first EV kit.

Evaluates: MAX16821B

MAX16821B Evaluation Kit

2 _______________________________________________________________________________________

Component List (continued)

DESIGNATION QTY DESCRIPTION

R7 1

0.15

±1%, 0.5W sense resistor

(1206)

IRC LRC-LRC1206LF-01-R150-F

R8 1 1

±5% resistor (0603)

R9 1 2k

±1% resistor (0603)

R11 1 2.49k

±1% resistor (0603)

R12 1 1.24k

±1% resistor (0603)

Component Suppliers

SUPPLIER PHONE WEBSITE

Central Semiconductor Corp. 631-435-1110 www.centralsemi.com

Diodes Inc. 805-446-4800 www.diodes.com

IRC Inc. 361-992-7900 www.irctt.com

Murata Mfg. Co., Ltd. 770-436-1300 www.murata.com

Sumida Corp. 847-545-6700 www.sumida.com

Taiyo Yuden 800-348-2496 www.t-yuden.com

Vishay 203-268-6261 www.vishay.com

EP = Exposed pad.

Note: Indicate that you are using the MAX16821B when contacting these component suppliers.

DESIGNATION QTY DESCRIPTION

R13 1 1k

±1% resistor (0603)

U1 1

Maxim PWM LED driver controller

MAX16821BATI+ (28-pin thin

QFN-EP*, 5mm x 5mm x 0.8mm)

— 1 PCB: MAX16821B Evaluation Kit+

LED Output Current

The MAX16821B delivers 660mA into an LED string

rated up to a maximum of 28V. Resistor R7 sets the

MAX16821B EV kit LED output current. Use the follow-

ing equation to calculate R7 when reconfiguring the

LED current:

where 100mV is the MAX16821B regulated SENSE+

to SENSE- differential current-sense voltage and ILED is

the desired LED current.

Input Current-Limit Setting

Current-sense resistor R6 sets the EV kit’s circuit aver-

age input current limit to 3.75A. During an overload

condition at low line, the MAX16821B regulates the

average input current to 3.75A. Use the following equa-

tion to calculate a new R6 value when reconfiguring the

input current limit:

where IIN is the input current limit.

For additional information, refer to the

Average Current

Limit

section in the MAX16821A/MAX16821B/MAX16821C

IC data sheet for setting the input current limit when

configuring the MAX16821B in a boost configuration.

LED Brightness Dimming

The LED brightness can be dimmed using a PWM sig-

nal with a 5V logic-high level and frequency range of

100Hz to 5kHz. Connect the PWM signal to the

PWMDIM and SGND PCB pads to control the LEDs’

brightness.

Output Overvoltage Protection

The maximum voltage on the LED+ pin is limited to 33V,

with respect to GND, by a resistor feedback network

formed by resistors R1 and R2. When the voltage at

LED+ exceeds the programmed 33V threshold, the

low-side driver turns off to prevent current through the

LED string connected between LED+ and LED-. Use

the following equation to calculate R1 and R2 resistor

values for a new overvoltage threshold:

where VOV_LIM is the desired overvoltage threshold, R2

is typically 10kΩ, and VOV is 1.276V.

Switching Frequency

The MAX16821B EV kit switching frequency (fSW) is

configured to 500kHz by resistor R4. To reconfigure the

MAX16821B switching frequency from 125kHz to

1.5MHz, use the equations below to calculate the new

value for R4:

where fSW is the desired switching frequency.

When reconfiguring the MAX16821B EV kit switching

frequency, other components may need to be changed

for proper stable operation.

Clock Output

The MAX16821B EV kit also features a clock output sig-

nal that is 180° out-of-phase with respect to MOSFET

N5. The clock output is available at the CLKOUT PCB

pad. Use the SGND PCB pad as a reference ground for

the CLKOUT signal.

Output Enable (EN)

The MAX16821B is enabled through pullup resistor R5.

To disable the MAX16821B EV kit, connect the EN PCB

pad to the SGND pad.

ffor k R k

464 10 40 4 120

4625 10 120 4 500

. ,

=≤≤

ΩΩ

RR VV

OV LIM OV

=× −

()

RmV

IIN

626 4

RmV

ILED

7100

Evaluates: MAX16821B

MAX16821B Evaluation Kit

_______________________________________________________________________________________ 3

Evaluates: MAX16821B

MAX16821B Evaluation Kit

4 _______________________________________________________________________________________4 _______________________________________________________________________________________

231

5, 6, 7, 8

CSP

LED+

10μF

50V

0.007Ω

1Ω

0.15Ω

PWMDIM

10μF

50V

4.7μF

VCC

MAX16821B

EN VIN

PGND

LED+

LED-

PGND SGND

VIN

MODE

SGND

RT/SYNC

LED+

CLKOUT

OUTV

I.C.

OVI

16 CLP

17 EAOUT

18 EAN

19 DIFF

20 CSN

21 CSP

N.C. 2

N.C. 7

DH 6

LX 5

BST 4

DL 3

PGND 1

VDD 28

VCC

0.1μF

SENSE+

SENSE-

SGND

1000pF

SHORTED

VCC

10kΩ

249kΩ

VCC

PWMDIM

CSP

R13

1kΩ

10kΩ

R11

2.49kΩ

R12

1.24kΩ

1000pF

C10

0.1μF

10μF

50V

8.8μH

0.1μF

50V

124kΩ

SGND

CLKOUT

SGND

OUTV

PWMDIM

1, 2, 5, 6

3N6

0.022μF

2kΩ

CLP

VCC

R10

10kΩ

Figure 1. MAX16821B EV Kit Schematic

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.

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

Evaluates: MAX16821B

MAX16821B Evaluation Kit

Figure 2. MAX16821B EV Kit Component Placement Guide—

Component Side

Figure 3. MAX16821B EV Kit PCB Layout—Component Side

Figure 4. MAX16821B EV Kit PCB Layout—Solder Side