Datasheet

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General Description

The MAX16821A, MAX16821B, and MAX16821C pulse-

width-modulation (PWM) LED driver controllers provide

high output-current capability in a compact package with a

minimum number of external components. The

MAX16821A–MAX16821C are suitable for use in synchro-

nous 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 HB LEDs.

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–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 fre-

quency 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

● LCD TVs and Display Backlight

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

Typical Operating Circuit and Selector Guide appears at

end of data sheet.

+Denotes lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

PART

TEMP RANGE PIN-PACKAGE

MAX16821AATI+

-40°C to +125°C 28 TQFN-EP*

MAX16821BATI+

-40°C to +125°C 28 TQFN-EP*

MAX16821CATI+

-40°C to +125°C 28 TQFN-EP*

HIGH-FREQUENCY

PULSE TRAIN

LED

7V TO 28V

CSP

PGND

I.C.

OVI

CLP

MAX16821

MAX16821A/MAX16821B/

MAX16821C

High-Power Synchronous HBLED

Drivers with Rapid Current Pulsing

19-0881; Rev 3; 4/14

Simplied Diagram

Ordering Information

EVALUATION KIT AVAILABLE

Summary of content (24 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX16821A/MAX16821B/ MAX16821C General Description The MAX16821A, MAX16821B, and 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–MAX16821C are suitable for use in synchronous and nonsynchronous step-down (buck), boost, buckboost, SEPIC, and Cuk LED drivers.
PAGE 2
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Absolute Maximum Ratings 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 (VBST - VLX) + 0.3V DL to PGND..............................................-0.
PAGE 3
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing 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 1500 kHz OSCILLATOR Switching Frequency Range Switching Frequency 125 fSW Switching Frequency Accuracy RT = 500kΩ 120 125 130 RT = 120kΩ 495 521 547 RT = 39.
PAGE 4
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing 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 1.
PAGE 5
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing 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 2.437 2.5 2.562 V 16.5 µA ENABLE INPUT (EN) EN Input-Voltage High EN rising EN Input Hysteresis 0.28 EN Pullup Current IEN 13.
PAGE 6
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Typical Operating Characteristics (continued) (VIN = 12V, VDD = VCC = 5V, TA = +25°C, unless otherwise noted.
PAGE 7
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Pin Description PIN NAME 1 PGND 2, 7 N.C. 3 DL 4 BST FUNCTION Power-Supply Ground No Connection. Not internally connected. Low-Side Gate-Driver Output Boost-Flying Capacitor Connection. Reservoir capacitor connection for the high-side MOSFET driver supply. Connect a ceramic capacitor between BST and LX.
PAGE 8
MAX16821A/MAX16821B/ MAX16821C Detailed Description The MAX16821A, MAX16821B, and MAX16821C are high-performance average current-mode PWM controllers for high-power and high-brightness LEDs (HB LEDs). 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.
PAGE 9
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing VCC MAX16821A MAX16821B MAX16821C EN 0.5 x VCC IN UVLO POR TEMP SEN +5V LDO VCC TO INTERNAL CIRCUIT I.C. CLP CSP AV = 34.5 CSN VCM AV = 4 gm VCLAMP LOW OUTV BST VCLAMP HIGH RT/SYNC OSCILLATOR CLKOUT S PWM COMPARATOR CLK LX MUX R Q VDD DL PGND 2 x fS RAMP GENERATOR DH Q VTH DIFF SENSESENSE+ VCM DIFF AMP MODE EAOUT EAN ERROR AMP VREF = 0.6V 0.
PAGE 10
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Once the MAX16821A–MAX16821C are synchronized to an external clock, the external clock cannot be removed if reliable operation is to be maintained. The differential current-sense amplifier (CSA) provides a 34.5V/V DC gain. The typical input offset voltage of the current-sense amplifier is 0.1mV with a 0 to 5.5V common-mode voltage range (VIN = 7V to 28V).
PAGE 11
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing error amplifier output (CLP) is connected to the inverting input of the PWM comparator. CLP is also externally accessible to provide frequency compensation for the inner current regulation loop (Figure 2).
PAGE 12
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing output and the internal reference voltage. The VEA output clamps to 0.93V relative to the internal common- mode voltage, VCM (+0.6V), limiting the average maximum current. The maximum average current-limit threshold is equal to the maximum clamp voltage of the VEA divided by the gain (34.5) of the current-sense amplifier. This results in accurate settings for the average maximum current. voltage (VCM).
PAGE 13
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Applications Information to the output. The output voltage cannot go below the input voltage in this configuration. Resistor R1 senses the inductor current and resistor R2 senses the LED current. The outer LED current regulation loop programs the average current in the inductor, thus achieving tight LED current regulation.
PAGE 14
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Input-Referenced Buck-Boost LED Driver output to the input. This effectively removes the boostonly restriction of the regulator in Figure 5, allowing the voltage across the LED to be greater or less than the input voltage. LED current-sensing is not ground-referenced, so a high-side current-sense amplifier is used to measure current. The circuit in Figure 6 shows a step-up/step-down regulator.
PAGE 15
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing SEPIC LED Driver with L2 to provide current to recharge C1 and supplies the load current. Since the voltage waveform across L1 and L2 are exactly the same, it is possible to wind both inductors on the same core (a coupled inductor). Although voltages on L1 and L2 are the same, RMS currents can be quite different so the windings may require a different gauge wire.
PAGE 16
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Low-Side Buck Driver with Synchronous Rectification current-loop inductor, current is sensed by resistor R1. To regulate the LED current, R2 creates a voltage that the differential amplifier compares to 0.6V. Capacitor C1 is small and helps reduce the ripple current in the LEDs. Omit C1 in cases where the LEDs can tolerate a higher ripple current.
PAGE 17
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing High-Side Buck Driver with Synchronous Rectification current-sense amplifier, U2. The voltage appearing across resistor R11 becomes the average inductor current-sense voltage for the inner average current loop. To regulate the LED current, R2 creates a voltage that the differential amplifier compares to its internal reference. Capacitor C1 is small and is added to reduce the ripple current in the LEDs.
PAGE 18
MAX16821A/MAX16821B/ MAX16821C Inductor Selection The switching frequency, peak inductor current, and allowable ripple at the output determine the value and size of the inductor. Selecting higher switching frequencies reduces inductance requirements, but at the cost of efficiency. The charge/discharge cycle of the gate and drain capacitance in the switching MOSFETs create switching losses worsening at higher input voltages, since switching losses are proportional to the square of the input voltage.
PAGE 19
MAX16821A/MAX16821B/ MAX16821C Use low-ESR ceramic capacitors with high ripple-current capability at the input. In the case of the boost topology where the inductor is in series with the input, the ripple current in the capacitor is the same as the inductor ripple and the input capacitance is small. Output Capacitors The function of the output capacitor is to reduce the output ripple to acceptable levels. The ESR, ESL, and the bulk capacitance of the output capacitor contribute to the output ripple.
PAGE 20
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Boost: R CF ≤ For adequate phase margin at crossover, place the zero formed by RCF and CCZ at least 3 to 5 times below the crossover frequency. The pole formed by RCF and CCP is added to eliminate noise spikes riding on the current waveform and is placed at the switching frequency.
PAGE 21
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing VCC VLED R4 VCC R8 ON/OFF C3 R10 VIN 7V TO 28V R3 Q5 R9 PWM DIM C2 Q4 14 I.C. C11 C10 R7 C9 R6 PWM DIM Q3 C8 12 11 EN 9 10 MODE CLKOUT 8 SGND 15 OVI N.C. 7 16 CLP DH 6 17 EAOUT LX 5 18 EAN R5 13 OUTV RT/SYNC MAX16821A MAX16821B MAX16821C DL 3 20 CSN N.C.
PAGE 22
MAX16821A/MAX16821B/ MAX16821C PCB Layout Use the following guidelines to layout the LED driver. High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Selector Guide 1) Place the IN, VCC, and VDD bypass capacitors close to the MAX16821A–MAX16821C. PART 2) Minimize the area and length of the high-current switching loops. DIFFERENTIAL SET VALUE (VSENSE+ - VSENSE-) (V) MAX16821A 0.60 1 MAX16821B 0.10 6 MAX16821C 0.
PAGE 23
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Typical Operating Circuit VCC VLED R4 ON/OFF R9 R3 R10 14 I.C. C11 C10 R9 C9 R7 13 C3 12 OUTV RT/SYNC 11 EN 9 10 MODE CLKOUT VIN 7V TO 28V 8 SGND 15 OVI N.C. 7 16 CLP DH 6 C2 Q1 VLED L1 17 EAOUT C8 18 EAN R6 LX 5 MAX16821A MAX16821B MAX16821C BST 4 19 DIFF DL 3 20 CSN N.C.
PAGE 24
MAX16821A/MAX16821B/ MAX16821C High-Power Synchronous HBLED Drivers with Rapid Current Pulsing Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 0 7/07 Initial release 1 3/09 Updated Electrical Characteristics table. 2 1/10 — — 3 4/14 No /V OPNs; removed automotive references from Applications section 1 DESCRIPTION — 3, 4 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.