MAXIM MAX16821A, MAX16821B, MAX16821C Technical data

General Description

The MAX16821A/MAX16821B/MAX16821C pulsewidth-modulation (PWM) LED driver controllers provide high output-current capability in a compact package with a minimum number of external components. The MAX16821A/MAX16821B/MAX16821C are suitable for use in synchronous and nonsynchronous step-down (buck), boost, buck-boost, SEPIC, and Cuk LED drivers. A logic input (MODE) allows the devices to switch between synchronous buck and boost modes of operation. These devices are the first high-power drivers designed specifically to accommodate common-anode HBLEDs.

The ICs offer average current-mode control that enable the use of MOSFETs with optimal charge and on-resistance figure of merit, thus minimizing the need for external heatsinking even when delivering up to 30A of LED current.

The differential sensing scheme provides accurate control of the LED current. The ICs operate from a 4.75V to

5.5V supply range with the internal regulator disabled (V

connected to IN). These devices operate from a 7V to 28V input supply voltage with the internal regulator enabled.

The MAX16821A/MAX16821B/MAX16821C feature a clock output with 180° phase delay to control a second out-of-phase LED driver to reduce input and output filter capacitor size and to minimize ripple currents. The wide switching frequency range (125kHz to 1.5MHz) allows the use of small inductors and capacitors.

Additional features include programmable overvoltage protection and an output enable function.

Applications

Front Projectors/Rear Projection TVs

Portable and Pocket Projectors

Automotive Exterior Lighting

LCD TVs and Display Backlight

Automotive Emergency Lighting and Signage

Features

♦ Up to 30A Output Current ♦ True-Differential Remote Output Sensing ♦ Average Current-Mode Control ♦ 4.75V to 5.5V or 7V to 28V Input-Voltage Range ♦ 0.1V/0.03V LED Current-Sense Options Maximize

Efficiency (MAX16821B/MAX16821C)

♦ Thermal Shutdown ♦ Nonlatching Output Overvoltage Protection ♦ Low-Side Buck Mode with or without

Synchronous Rectification

♦ High-Side Buck and Low-Side Boost Mode with or

without Synchronous Rectification

♦ 125kHz to 1.5MHz Programmable/Synchronizable

Switching Frequency

♦ Integrated 4A Gate Drivers ♦ Clock Output for 180° Out-of-Phase Operation for

Second Driver

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

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED

Drivers with Rapid Current Pulsing

________________________________________________________________

Maxim Integrated Products

Simplified Diagram

19-0881; Rev 0; 7/07

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

Typical Operating Circuit and Selector Guide appear at end of data sheet.

Ordering Information

Denotes a lead-free package.

EP = Exposed pad.

PART TEMP RANGE

MAX16821AATI+ -40°C to +125°C 28 TQFN-EP* T2855-8

MAX16821BATI+ -40°C to +125°C 28 TQFN-EP* T2855-8

MAX16821CATI+ -40°C to +125°C 28 TQFN-EP* T2855-8

PINPACKAGE

PKG

CODE

7V TO 28V

LED

I.C.

OVI

CLP

MAX16821

CSP

PGND

PULSE TRAIN

HIGH-FREQUENCY

NOTE: MAXIM PATENT-PENDING TOPOLOGY

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= 5V, VDD= VCC, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)

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.

IN to SGND.............................................................-0.3V to +30V

BST to SGND..........................................................-0.3V to +35V

BST to LX..................................................................-0.3V to +6V

DH to LX...........................................-0.3V to (V

BST

- VLX) + 0.3V

DL to PGND................................................-0.3V to (V

+ 0.3V)

to SGND............................................................-0.3V to +6V

, VDDto PGND ...................................................-0.3V to +6V

SGND to PGND .....................................................-0.3V to +0.3V

Current ......................................................................300mA

All Other Pins to SGND...............................-0.3V to (V

+ 0.3V)

Continuous Power Dissipation (T

= +70°C) 28-Pin TQFN 5mm x 5mm (derate 34.5mW/°C

above +70°C) ............................................................2758mW

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

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Input-Voltage Range V

Quiescent Supply Current I

LED CURRENT REGULATOR

Differential Set Value (V

SENSE

+ to V

SENSE-

) (Note 2)

Soft-Start Time t

STARTUP/INTERNAL REGULATOR

U nd er vol tag e Lockout ( U V LO ) UVLO VCC rising 4.1 4.3 4.5 V

C C

UVLO Hysteresis VCC falling 200 mV

Output Voltage VIN = 7V to 28V, I

MOSFET DRIVER

Output Driver Impedance Low or high output, I

Output Driver Source/Sink Current IDH, I

Nonoverlap Time t

Internal LDO on 7 28

Internal LDO off (V

VEN = VCC or SGND, no switching 2.7 5.5 mA

VIN = VCC = 4.75V to 5.5V, fSW = 500kHz (MAX16821A)

VIN = 7V to 28V, fSW = 500kHz (MAX16821A)

VIN = VCC = 4.75V to 5.5V, fSW = 500kHz (MAX16821B)

VIN = 7V to 28V, fSW = 500kHz (MAX16821B)

VIN = VCC = 4.75V to 5.5V, fSW = 500kHz (MAX16821C)

= 7V to 28V, fSW = 500kHz

(MAX16821C)

= 5nF 35 ns

DH/DL

connected to VIN) 4.75 5.50

= 0 to 60mA 4.85 5.10 5.30 V

SOURCE

SOURCE/SINK

= 20mA 1.1 3 Ω

0.594 0.600 0.606

0.098 0.100 0.102

0.028 0.030 0.032

1024

Clock

Cycles

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED

Drivers with Rapid Current Pulsing

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 5V, VDD= VCC, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)

)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

OSCILLATOR

Switching Frequency Range 125 1500 kHz

RT = 500kΩ 120 125 130

Switching Frequency Accuracy

CLKOUT Phase Shift with Respect to DH (Rising Edges)

CLKOUT Phase Shift with Respect to DL (Rising Edges)

CLKOUT Output-Voltage Low V

CLKOUT Output-Voltage High V

SYNC Input High Pulse Width t

SYNC Input Clock High Threshold V

SYNC Input Clock Low Threshold V

SYNC Pullup Current I

SYNC Power-Off Level V

INDUCTOR CURRENT LIMIT

Average Current-Limit Threshold V

Reverse Current-Limit Threshold V

Cycle-by-Cycle Current Limit CSP to CSN 60 mV

Cycle-by-Cycle Overload

CURRENT-SENSE AMPLIFIER

CSP to CSN Input Resistance R

Common-Mode Range V

Input Offset Voltage V

Amplifier Voltage Gain A

3dB Bandwidth f

CURRENT-ERROR AMPLIFIER (TRANSCONDUCTANCE AMPLIFIER)

Transconductance g

Open-Loop Gain A

SYNC

SYNCH

SYNCL

SYNC_OUTVRT/SYNC

SYNC_OFF

CLR

CMR(CS

OS(CS)

V(CS)

3dB

VL(CE)

RT = 120kΩ 495 521 547Switching Frequency f

RT = 39.9kΩ 1515 1620 1725

120kΩ < RT ≤ 500kΩ -5 +5

40kΩ ≤ R

SINK

SOURCE

CSP to CSN 26.4 27.5 30.0 mV

CSP to CSN -2.0 mV

CSP

VIN = 7V to 28V 0 5.5 V

≤ 120kΩ -8 +8

= 125kHz, MODE connected to SGND 180

= 125kHz, MODE connected to V

= 2mA 0.4 V

= 2mA 4.5 V

= 0V 250 500 µA

to V

= 75mV 260 ns

CSN

200 ns

180

0.4 V

4kΩ

0.1 mV

34.5 V/V

4 MHz

550 µS

50 dB

kHz

Degrees

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 5V, VDD= VCC, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)

)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

LED CURRENT SIGNAL DIFFERENTIAL VOLTAGE AMPLIFIER (DIFF)

Common-Mode Voltage Range V

DIFF Output Voltage V

Input Offset Voltage V

SENSE+ to SENSE- Input Resistance

OUTV AMPLIFIER

Gain-Bandwidth Product V

3dB Bandwidth V

Output Sink Current 30 µA

Output Source Current 80 µA

Maximum Load Capacitance 50 pF

OUTV to (CSP - CSN) Transfer Function

Input Offset Voltage 1mV

VOLTAGE-ERROR AMPLIFIER (EAOUT)

Open-Loop Gain A

Unity-Gain Bandwidth f

EAN Input Bias Current I

Error Amplifier Output Clamping Voltage

INPUTS (MODE AND OVI)

MODE Input-Voltage High 2V

MODE Input-Voltage Low 0.8 V

MODE Pulldown Current 456µA

OVI Trip Threshold OVP

OVI Hysteresis OVI

OVI Input Bias Current I

CMR(DIFF

OS(DIFF

V(DIFF)

3dB

VOLEA

GBW

B(EA)

CLAMP(EA

HYS

OVI

MAX16821A -3.7 +3.7

MAX16821B/MAX16821C -1.5 +1.5

MAX16821A 0.992 1 1.008

MAX16821B 5.9 6 6.1Amplifier Voltage Gain A

MAX16821C 18.5 20 21.5

MAX16821A, C

MAX16821B, C

MAX16821C, C

MAX16821A 50 100

MAX16821B 30 60

MAX16821C 10 20

4mV ≤ C

With respect to V

= V

SENSE+

= 2V 4 MHz

OUTV

= 2V 1 MHz

OUTV

- CSN ≤ 32mV 132.5 135 137.7 V/V

= 2V -0.2 +0.03 +0.2 µA

EAN

= 1V 0.2 µA

OVI

= 0V 0.6 V

SENSE-

= 20pF 1.7 MHz

DIFF

= 20pF 16003dB Bandwidth f

DIFF

= 20pF 550

DIFF

0 1.0 V

V/V

kHz

kΩ

70 dB

3 MHz

905 930 940 mV

1.244 1.276 1.308 V

200 mV

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED

Drivers with Rapid Current Pulsing

_______________________________________________________________________________________ 5

Note 1: All devices are 100% production tested at +25°C. Limits over temperature are guaranteed by design. Note 2: Does not include an error due to finite error amplifier gain. See the

Voltage-Error Amplifier

section.

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 5V, VDD= VCC, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)

Typical Operating Characteristics

(VIN= 12V, VDD= V

= 5V, TA= +25°C, unless otherwise noted.)

SUPPLY CURRENT (IQ) vs. FREQUENCY

MAX16821A toc01

FREQUENCY (kHz)

SUPPLY CURRENT (mA)

1300900 1100500 700300

100 1500

VIN = 24V

EXTERNAL CLOCK NO DRIVER LOAD

VIN = 5V

VIN = 12V

SUPPLY CURRENT vs. TEMPERATURE

MAX16821A toc02

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

603510-15

-40 85

VIN = 12V C

DH/DL

= 22nF

VCC LOAD REGULATION vs. V

MAX16821A toc03

VCC LOAD CURRENT (mA)

(V)

13512090 10530 45 60 7515

4.6

4.7

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

4.5 0150

VIN = 24V

VIN = 7V

VIN = 12V

DRIVER RISE TIME

vs. DRIVER LOAD CAPACITANCE

MAX16821A toc04

LOAD CAPACITANCE (nF)

(ns)

2015510

100

120

140

160

180

200

025

DRIVER FALL TIME

vs. DRIVER LOAD CAPACITANCE

MAX16821A toc05

LOAD CAPACITANCE (nF)

(ns)

2015510

100

025

HIGH-SIDE DRIVER (DH) SINK

AND SOURCE CURRENT

MAX16821A toc06

2A/div

100ns/div

LOAD

= 22nF

= 12V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

ENABLE INPUT (EN)

EN Input-Voltage High EN rising 2.437 2.5 2.562 V

EN Input Hysteresis 0.28 V

EN Pullup Current I

13.5 15 16.5 µA

THERMAL SHUTDOWN

Thermal Shutdown 165 °C

Thermal-Shutdown Hysteresis 20 °C

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VIN= 12V, VDD= V

= 5V, TA= +25°C, unless otherwise noted.)

LOW-SIDE DRIVER (DL) SINK

AND SOURCE CURRENT

= 22nF

LOAD

= 12V

100ns/div

LOW-SIDE DRIVER (DL) RISE TIME

= 22nF

LOAD

= 12V

MAX16821A toc07

MAX16821A toc10

3A/div

2V/div

HIGH-SIDE DRIVER (DH) RISE TIME

VIN = 12V DH RISING

40ns/div

LOW-SIDE DRIVER (DL) FALL TIME

MAX16821A toc08

LOAD

= 12V

MAX16821A toc11

= 22nF

2V/div

10,000

(kHz)

1000

HIGH-SIDE DRIVER (DH) FALL TIME

= 22nF

LOAD

= 12V

40ns/div

FREQUENCY vs. R

VIN = 12V

MAX16821A toc09

2V/div

MAX16821A toc12

40ns/div

100

30 550

FREQUENCY vs. TEMPERATURE

260

VIN = 12V

258

256

254

252

(kHz)

250

248

246

244

242

240

035

TEMPERATURE (°C)

3020 2551015

SYNC, CLKOUT, AND DH WAVEFORMS

MAX16821A toc13

1μs/div

MAX16821A toc14

MODE = SGND

RT/SYNC 5V/div 0V

CLKOUT 5V/div

DH 5V/div 0V

SYNC, CLKOUT, AND DL WAVEFORMS

190

230 270 310

RT (kΩ)

1μs/div

430 470 510350 39 070 110 150

MODE = V

MAX16821A toc15

RT/SYNC 5V/div 0V

CLKOUT 5V/div

DL 5V/div 0V

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED

Drivers with Rapid Current Pulsing

_______________________________________________________________________________________ 7

Pin Description

PIN NAME FUNCTION

1 PGND Power-Supply Ground

2, 7 N.C. No Connection. Not internally connected.

3 DL Low-Side Gate-Driver Output

4 BST

5 LX High-Side MOSFET Source Connection

6 DH High-Side Gate-Driver Output

8, 22, 25 SGND

9 CLKOUT

10 MODE

11 EN

12 RT/SYNC

13 OUTV

14 I.C. Internally Connected. Connect to SGND for proper operation.

15 OVI

16 CLP Current-Error-Amplifier Output. Compensate the current loop by connecting an RC network to ground.

17 EAOUT Voltage-Error-Amplifier Output. Connect EAOUT to the external gain-setting network.

18 EAN Voltage-Error-Amplifier Inverting Input

19 DIFF

20 CSN

21 CSP

23 SENSE-

24 SENSE+

26 IN Supply Voltage Input. Connect IN to VCC, for a 4.75V to 5.5V input supply range.

27 V

28 V

—EP

Boost-Flying Capacitor Connection. Reservoir capacitor connection for the high-side MOSFET driver supply. Connect a ceramic capacitor between BST and LX.

Signal Ground. SGND is the ground connection for the internal control circuitry. Connect SGND and PGND together at one point near the IC.

Oscillator Output. If MODE is low, the rising edge of CLKOUT phase shifts from the rising edge of DH by 180°. If MODE is high, the rising edge of CLKOUT phase shifts from the rising edge of DL by 180°.

Buck/Boost Mode Selection Input. Drive MODE low for low-side buck mode operation. Drive MODE high for boost or high-side buck mode operation. MODE has an internal 5µA pulldown current to ground.

Output Enable. Drives EN high or leave unconnected for normal operation. Drive EN low to shut down the power drivers. EN has an internal 15µA pullup current.

Switching Frequency Programming. Connect a resistor from RT/SYNC to SGND to set the internal oscillator frequency. Drive RT/SYNC to synchronize the switching frequency with an external clock.

Inductor Current-Sense Output. OUTV is an amplifier output voltage proportional to the inductor current. The voltage at OUTV = 135 x (V

Overvoltage Protection. When OVI exceeds the programmed output voltage by 12.7%, the low-side and the high-side drivers are turned off. When OVI falls 20% below the programmed output voltage, the drivers are turned on after power-on reset and soft-start cycles are completed.

Differential Remote-Sense Amplifier Output. DIFF is the output of a precision amplifier with SENSE+ and SENSE- as inputs.

Current-Sense Differential Amplifier Negative Input. The differential voltage between CSN and CSP is amplified internally by the current-sense amplifier (Gain = 34.5) to measure the inductor current.

Current-Sense Differential Amplifier Positive Input. The differential voltage between CSP and CSN is amplified internally by the current-sense amplifier (Gain = 34.5) to measure the inductor current.

Differential LED Current-Sensing Negative Input. Connect SENSE- to the negative side of the LED currentsense resistor or to the negative feedback point.

Differential LED Current-Sensing Positive Input. Connect SENSE+ to the positive side of the LED currentsense resistor, or to the positive feedback point.

Internal +5V Regulator Output. VCC is derived from VIN. Bypass VCC to SGND with 4.7µF and 0.1µF

ceramic capacitors.

Low-Side Driver Supply Voltage

Exposed Pad. EP is internally connected to SGND. Connect EP to a large-area ground plane for effective power dissipation. Connect EP to SGND. Do not use as a ground connection.

CSP

- V

CSN

MAX16821A/MAX16821B/MAX16821C

High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

8 _______________________________________________________________________________________

Detailed Description

The MAX16821A/MAX16821B/MAX16821C are high-performance average current-mode PWM controllers for high-power and high-brightness LEDs (HBLEDs). The average current-mode control technique offers inherently stable operation, reduces component derating and size by accurately controlling the inductor current. The devices achieve high efficiency at high currents (up to 30A) with a minimum number of external components. A logic input (MODE) allows the LED driver to switch between buck and boost modes of operation.

The MAX16821A/MAX16821B/MAX16821C feature a CLKOUT output 180° out-of-phase with respect to either the high-side or low-side driver, depending on MODE’s logic level. CLKOUT provides the drive for a second out-of-phase LED driver for applications requiring reduced input capacitor ripple current while operating another LED driver.

The MAX16821A/MAX16821B/MAX16821C consist of an inner average current regulation loop controlled by an outer loop. The combined action of the inner current loop and outer voltage loop corrects the LED current errors by adjusting the inductor current resulting in a tightly regulated LED current. The differential amplifier (SENSE+ and SENSE- inputs) senses the LED current using a resistor in series with the LEDs and produces an amplified version of the sense voltage at DIFF. The resulting amplified sensed voltage is compared against an internal 0.6V reference at the error amplifier input.

Input Voltage

The MAX16821A/MAX16821B/MAX16821C operate with a 4.75V to 5.5V input supply range when the internal LDO is disabled (V

connected to IN) or a 7V to 28V input supply range when the internal LDO is enabled. For a 7V to 28V input voltage range, the internal LDO provides a regulated 5V output with 60mA of sourcing capability. Bypass V

to SGND with 4.7µF

and 0.1µF low-ESR ceramic capacitors.

The MAX16821A/MAX16821B/MAX16821C’s V

input provides supply voltage for the low-side and the highside MOSFET drivers. Connect V

to V

using an R-C filter to isolate the analog circuits from the MOSFET drivers. The internal LDO powers up the MAX16821A/ MAX16821B/MAX16821C. For applications utilizing a 5V input voltage, disable the internal LDO by connecting IN and VCCtogether. The 5V power source must be in the 4.75V to 5.5V range of for proper operation of the MAX16821A/MAX16821B/MAX16821C.

Undervoltage Lockout (UVLO)

The MAX16821A/MAX16821B/MAX16821C include UVLO and a 2048 clock-cycle power-on-reset circuit. The UVLO rising threshold is set to 4.3V with 200mV hysteresis. Hysteresis at UVLO eliminates chattering during startup. Most of the internal circuitry, including the oscillator, turns on when the input voltage reaches 4V. The MAX16821A/MAX16821B/MAX16821C draw up to 3.5mA of quiescent current before the input voltage reaches the UVLO threshold.

Soft-Start

The MAX16821A/MAX16821B/MAX16821C include an internal soft-start for a glitch-free rise of the output voltage. After 2048 power-on-reset clock cycles, a 0.6V reference voltage connected to the positive input of the internal error amplifier ramps up to its final value after 1024 clock cycles. Soft-start reduces inrush current and stress on system components. During soft-start, the LED current will ramp monotonically towards its final value.

Internal Oscillator

The internal oscillator generates a clock with the frequency inversely proportional to the value of R

(see

the

Typical Operating Circuit

). The oscillator frequency is adjustable from 125kHz to 1.5MHz range using a single resistor connected from RT/SYNC to SGND. The frequency accuracy avoids the overdesign, size, and cost of passive filter components like inductors and capacitors. Use the following equation to calculate the oscillator frequency:

For 120kΩ≤RT≤ 500kΩ:

For 40kΩ≤R

≤ 120kΩ:

The oscillator also generates a 2V

P-P

ramp signal for the PWM comparator and a 180° out-of-phase clock signal at CLKOUT to drive a second out-of-phase LED current regulator.

625 10

640 10

()=

+ 17 hidden pages