EinführungDas Anwendungsgebiet von LEDs umfasst mittlerweile alle denk-baren Einsatzbereiche von allgemeinen Beleuchtungen über den Automobilsektor, Industrie- und Prüfausrüstungen und Anzeigeta-feln bis hin zu Sicherheitsinstrumenten. Dementsprechend haben auch die an LED-Treiber gestellten Anforderungen zugenommen. Neueste LED-Lösungen verlangen nach Treibern, die kompakt, effizient und störungsarm sind und dabei große Dimmungsver-hältnisse und fortschrittliche Fehlerschutz-Features bieten. Der LT3922 erfüllt all diese Anforderungen. Der synchrone LED-Treiber LT3922 mit integrierten 2A/40V-Schal-tern ist als Boost-, Buck- oder Boost-Buck-LED-Treiber konfigu-rierbar und passt zusammen mit seinen hocheffizienten integ-rierten Schaltern in ein 4 x 5 mm großes QFN-Gehäuse. In den Baustein sind die fortschrittlichsten Schalt-Technologien von Linear Technology integriert. Hohe Schaltleistung ist auf wenig Platz konzentriert, und gleichzeitig wird die Flankensteilheit kon-trolliert, um unerwünschte Störaussendungen einzudämmen. Der LT3922 zeichnet sich durch kontrollierte Anstiegsgeschwindig-keiten ohne Überschwinger aus und trifft so den optimalen Mit-telweg zwischen hohem Wirkungsgrad und geringem Störungs-

aufkommen. Im Interesse kleiner Lösungsabmessungen werden Schaltfrequenzen bis zu 2,5 MHz unterstützt. Der winzige LED-Treiber LT3922 überzeugt durch sein geringes EMI-Aufkommen, seinen hohen Wirkungsgrad und seine Fehler-schutz-Features, die für den Einsatz im Automotive-Bereich be-nötigt werden. Er kommt mit den für Automotive-Anwendungen typischen Spannungsspitzen bis 36 V ebenso zurecht wie mit den bei Kaltstarts auftretenden Spannungseinbrüchen auf 3 V. Die Silent Switcher®-Architektur, die Spread-Spectrum-Frequenz-modulation (SSFM) und die kontrollierte Flankensteilheit machen den LT3922 zum idealen Baustein zum Ansteuern von LEDs mit minimalen Störungen. Die flexible Topologie des LT3922 eignet sich für Tagfahrlicht-Leuchten, Signalleuchten, Rückleuchten und Frontscheinwerfer-Segmente, aber auch für Armaturentafeln und Head-up-Displays mit großen Dimmungsverhältnissen. Die eingebauten Fehlerschutz-Funktionen verringern den Aufwand an zusätzlichen Bauteilen für den Schutz vor Kurzschlüssen und Stromkreisunterbrechungen in den LEDs.

Störungsarmer LED-Treiber mit integrierten synchronen 2A/40V-Schaltern für Kfz-BeleuchtungenDesign Note 557 Keith Szolushar

55V High Efficiency Buck-Boost Power Manager and Multi-Chemistry Battery ChargerDesign Note 531

Charlie Zhao

10/14/531

Figure 1. 15V to 55V Input, 25.2V/6.3A Buck-Boost Battery Charger

IntroductionToday, battery chargers are expected to easily support a variety of battery chemistries and accept a range of voltage inputs, including wide-ranging solar panels. It is increasingly common for input voltage ranges to span above and below the output battery voltage, requiring both step-down and step-up capability (buck-boost to-pology). The LTC4020 buck-boost power manager and multi-chemistry battery-charging controller can take wide-ranging 4.5V to 55V inputs and produce output voltages up to 55V. Its buck-boost DC/DC controller supports battery and system voltages above, below, or equal to the input voltage.

The charger is easily optimized for a variety of battery chemistries. For instance, it can follow a constant-current/constant-voltage (CC/CV) charge algorithm, with either C/10 or timed termination for lithium-based battery systems, a constant-current (CC) characteristic with timed termination, or an optimized 4-step, 3-stage lead-acid charge profile.

6.3A Charger for 25.2V Battery Float VoltageFigure 1 shows a 15V to 55V input, 25.2V/6.3A buck-boost battery charger, featuring a high efficiency 4-switch (M2–M5) synchronous buck-boost DC/DC L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.

dn531 F01

STAT2STAT1BST1BST2

SENSVINSENSTOP

INTVCC

SHDNVIN_REG

RNG/SSILIMIT

VFBMINVFBMAXVFB

FBG

NTCCSOUTMODE

R13100k

C50.22µF0603

SW1SW2

TG1

BG1

SENSBOT

SENSGND

BG2TG2CSP

CSN

BGATE

VBATVC

ITHTIMERRT

LTC4020

PVIN

SGND SGND PGND

R1536k0603

R1647k0603

M1Si7145DP

R18100Ω

R20100Ω

R263k

R273k

R1410k

C400.22µF

0603

C390.22µF

0603

C66.8nF0603

C547pF0603

C4100pF0603

C1, 0.1µF100V, 0603

GNDMODE

BAT25.2V FLOAT6.3A MAX

GND

VOUT21V TO 28V8A MAX

VOUTVBAT

R1920Ω

RCBAT10.008Ω

1W2512

C114.7µF6.3V0603

R1124.9k1%

R1024.9k0.1%

R9226k06031%

R8226k06030.1%

C120.033µF

RCBRB10.002 Ω1W2512

RCBRT10.002Ω1W2512

M4SiR664DP

M2SiR664DP

L15.6µH

WÜRTH 7443556560M3SiR422DP

M5SiR422DP

D6B360A

C190.22µF25V0603

C200.22µF25V0603

C2110µF6.3V0805

D1SBR0560S1

D2SBR0560S1 D4

GRN

D3RED

C1410µF35V1210

C1810µF35V

1210

C2710µF35V1210

C2810µF35V

1210

C15220µF35V35HVH220M

C17220µF

35V35HVH220M

+

+

R5OPT

R2510k

R1100k

R451k

R385.1Ω0805

C256µF63V

63HVH56M

C356µF63V63HVH56M

+

+

GND

VIN15V TO 55V

C23C164.7µF100V1210

VIN

VIN4V TO 30V

221k

31.6k

EN/UVLO

OVLO

VREF

PWM

CTRLANALOG DIMMING

SYNC/SPRD

INTVCCFAULT

FAULT

BSTSW

VOUT

VOUT

FB

RP VCRT

ISP

GND

ISN

PWMTG

ISMONLT3922

449k

1M

33.2k

100k

100k

91k

100k

24k

0.22nF

1µF

0.1µFL1

4.7µH

M1

300mΩ

COUT32.2µF50V

COUT1,COUT20.47µF

LED34V330mA

SS

45.3k2MHz

332k 33nF

2.2µF

COUT1, COUT2, C4, C5: 0402COUT3: 1206 D1: NXP PMEG4010CEJFB1: WÜRTH 7427920415FB2: WÜRTH 742792097L1: COILCRAFT XAL5050-223MEBM1: VISHAY Si2319CDS

D1

ON

EXT PWM

INT

OFFSYNCEXT

INTVCC(SSFM ON)

EXT

SYNC

PWMINT

PWMEXT OR ON

FERRITE BEADFB2

C50.1µF

2.2µF

4.7µF

C40.1µF

1µF

FERRITE BEADFB1

33µF50V

+

Low EMI LED Driver Features 2A, 40V, Integrated, Synchronous Switches for Automotive LightingDesign Note 557

Keith Szolusha

12/16/557

Figure 1. 2MHz Automotive Boost LED Driver Features Low EMI and Internally Generated PWM Dimming Has 91% Efficiency and Passes CISPR 25 Class 5 EMI

IntroductionThe breadth of LED applications has grown to encom-pass everything from general lighting to automotive, industrial and test equipment, sign boards and safety instruments. Feature requirements for LED drivers have become more extensive. The latest LED solu-tions require drivers that are compact, efficient, low noise, and have high dimming ratios and advanced fault protection. The LT3922 meets these demands.

The LT3922 synchronous LED driver with integrated 2A, 40V switches can be configured as a boost, buck or boost-buck LED driver. Its high efficiency integrated switches fit into a tiny 4mm × 5mm QFN package. This device integrates Linear’s most advanced switching technologies, condensing high power capability into tight spaces while controlling the edge rates and miti-gating unwanted EMI. The LT3922 features controlled switching edges that do not ring—offering just the

right balance of high efficiency and low noise. They can be run at up to 2.5MHz for compact solutions.

The tiny LT3922 LED driver features low EMI, high efficiency and fault protection required in automo-tive environments. It can handle 36V automotive transients and 3V cold crank. Its Silent Switcher® architecture, spread spectrum frequency modula-tion (SSFM) and controlled switching edges make it ideal for powering LEDs with low EMI. Its flexible topology is useful in daytime running lights, signal lights, taillights, and headlight segments as well as dashboard and heads-up displays with high dimming ratios. Built-in fault protection reduces the number of extra components required to protect against short and open LEDs.L, LT, LTC, LTM, Linear Technology, the Linear logo and Silent Switcher are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

VIN

VIN4V TO 30V

221k

31.6k

EN/UVLO

OVLO

VREF

PWM

CTRLANALOG DIMMING

SYNC/SPRD

INTVCCFAULT

FAULT

BSTSW

VOUT

VOUT

FB

RP VCRT

ISP

GND

ISN

PWMTG

ISMONLT3922

449k

1M

33.2k

100k

100k

91k

100k

24k

0.22nF

1µF

0.1µFL1

4.7µH

M1

300mΩ

COUT32.2µF50V

COUT1,COUT20.47µF

LED34V330mA

SS

45.3k2MHz

332k 33nF

2.2µF

COUT1, COUT2, C4, C5: 0402COUT3: 1206 D1: NXP PMEG4010CEJFB1: WÜRTH 7427920415FB2: WÜRTH 742792097L1: COILCRAFT XAL5050-223MEBM1: VISHAY Si2319CDS

D1

ON

EXT PWM

INT

OFFSYNCEXT

INTVCC(SSFM ON)

EXT

SYNC

PWMINT

PWMEXT OR ON

FERRITE BEADFB2

C50.1µF

2.2µF

4.7µF

C40.1µF

1µF

FERRITE BEADFB1

33µF50V

+

Low EMI LED Driver Features 2A, 40V, Integrated, Synchronous Switches for Automotive LightingDesign Note 557

Keith Szolusha

12/16/557

Figure 1. 2MHz Automotive Boost LED Driver Features Low EMI and Internally Generated PWM Dimming Has 91% Efficiency and Passes CISPR 25 Class 5 EMI

IntroductionThe breadth of LED applications has grown to encom-pass everything from general lighting to automotive, industrial and test equipment, sign boards and safety instruments. Feature requirements for LED drivers have become more extensive. The latest LED solu-tions require drivers that are compact, efficient, low noise, and have high dimming ratios and advanced fault protection. The LT3922 meets these demands.

The LT3922 synchronous LED driver with integrated 2A, 40V switches can be configured as a boost, buck or boost-buck LED driver. Its high efficiency integrated switches fit into a tiny 4mm × 5mm QFN package. This device integrates Linear’s most advanced switching technologies, condensing high power capability into tight spaces while controlling the edge rates and miti-gating unwanted EMI. The LT3922 features controlled switching edges that do not ring—offering just the

right balance of high efficiency and low noise. They can be run at up to 2.5MHz for compact solutions.

The tiny LT3922 LED driver features low EMI, high efficiency and fault protection required in automo-tive environments. It can handle 36V automotive transients and 3V cold crank. Its Silent Switcher® architecture, spread spectrum frequency modula-tion (SSFM) and controlled switching edges make it ideal for powering LEDs with low EMI. Its flexible topology is useful in daytime running lights, signal lights, taillights, and headlight segments as well as dashboard and heads-up displays with high dimming ratios. Built-in fault protection reduces the number of extra components required to protect against short and open LEDs.L, LT, LTC, LTM, Linear Technology, the Linear logo and Silent Switcher are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

VIN

VIN4V TO 30V

221k

31.6k

EN/UVLO

OVLO

VREF

PWM

CTRLANALOG DIMMING

SYNC/SPRD

INTVCCFAULT

FAULT

BSTSW

VOUT

VOUT

FB

RP VCRT

ISP

GND

ISN

PWMTG

ISMONLT3922

449k

1M

33.2k

100k

100k

91k

100k

24k

0.22nF

1µF

0.1µFL1

4.7µH

M1

300mΩ

COUT32.2µF50V

COUT1,COUT20.47µF

LED34V330mA

SS

45.3k2MHz

332k 33nF

2.2µF

COUT1, COUT2, C4, C5: 0402COUT3: 1206 D1: NXP PMEG4010CEJFB1: WÜRTH 7427920415FB2: WÜRTH 742792097L1: COILCRAFT XAL5050-223MEBM1: VISHAY Si2319CDS

D1

ON

EXT PWM

INT

OFFSYNCEXT

INTVCC(SSFM ON)

EXT

SYNC

PWMINT

PWMEXT OR ON

FERRITE BEADFB2

C50.1µF

2.2µF

4.7µF

C40.1µF

1µF

FERRITE BEADFB1

33µF50V

+

Low EMI LED Driver Features 2A, 40V, Integrated, Synchronous Switches for Automotive LightingDesign Note 557

Keith Szolusha

12/16/557

Figure 1. 2MHz Automotive Boost LED Driver Features Low EMI and Internally Generated PWM Dimming Has 91% Efficiency and Passes CISPR 25 Class 5 EMI

IntroductionThe breadth of LED applications has grown to encom-pass everything from general lighting to automotive, industrial and test equipment, sign boards and safety instruments. Feature requirements for LED drivers have become more extensive. The latest LED solu-tions require drivers that are compact, efficient, low noise, and have high dimming ratios and advanced fault protection. The LT3922 meets these demands.

The LT3922 synchronous LED driver with integrated 2A, 40V switches can be configured as a boost, buck or boost-buck LED driver. Its high efficiency integrated switches fit into a tiny 4mm × 5mm QFN package. This device integrates Linear’s most advanced switching technologies, condensing high power capability into tight spaces while controlling the edge rates and miti-gating unwanted EMI. The LT3922 features controlled switching edges that do not ring—offering just the

right balance of high efficiency and low noise. They can be run at up to 2.5MHz for compact solutions.

The tiny LT3922 LED driver features low EMI, high efficiency and fault protection required in automo-tive environments. It can handle 36V automotive transients and 3V cold crank. Its Silent Switcher® architecture, spread spectrum frequency modula-tion (SSFM) and controlled switching edges make it ideal for powering LEDs with low EMI. Its flexible topology is useful in daytime running lights, signal lights, taillights, and headlight segments as well as dashboard and heads-up displays with high dimming ratios. Built-in fault protection reduces the number of extra components required to protect against short and open LEDs.L, LT, LTC, LTM, Linear Technology, the Linear logo and Silent Switcher are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Bild 1. Mit 2 MHz schaltender Aufwärtswandler, eingesetzt als LED-Treiber für Automotive-Anwendungen. Die Schaltung bietet geringe Störaussendungen und intern erzeugte PWM-Dimmung, erreicht 91 % Wirkungsgrad und erfüllt die EMI-Anforderungen gemäß CISPR 25 Klasse 5.

Eingebaute Features ergeben niedriges EMI-NiveauDer LT3922 enthält eine Vielzahl von Features, mit denen er problemlos ein niedriges EMI-Niveau erreichen kann. Als erstes ist hier die patentierte Silent Switcher-Architektur von Linear Technology anzuführen. Diese basiert darauf, die Größe der un-ter Strom schaltenden Schleifen zu minimieren, die Steilheit der Schaltflanken zu kontrollieren und keine Überschwinger auftre-ten zu lassen. Die Anschlussbelegung erlaubt ferner die Platzie-rung kleiner Hochfrequenz-Kondensatoren ganz in der Nähe der beiden VOUT-Pins, um die Größe der unter Strom geschalteten Stromschleifen und damit das EMI-Aufkommen zu verringern. Die Kontrolle der Flankensteilheit durch das IC eliminiert die hochfre-quenten Schwingungen, zu denen es bei Wandlern ohne dieses Feature üblicherweise kommt. Ohne Abstriche an der Leistung oder am Wirkungsgrad wird hierdurch eine Reduzierung der Hochfrequenz-Störungen erreicht. Die SSFM-Funktion des LT3922 lässt die per Widerstand festge-legte Schaltfrequenz zwischen 100 % und 125 % ihres nominel-len Werts pendeln. Hierdurch verringern sich die maximalen und durchschnittlichen Störaussendungen des Wandlers bei hohen ebenso wie bei niedrigen Frequenzen. Boost-, Buck- oder Boost-Buck-KonfigurationLEDs sind Lichtquellen, die mit einem geregelten Strom ange-steuert werden. Deshalb können LED+ und/oder LED- an mas-sefremde Potenziale angeschlossen werden, und als LED-Treiber kommen Auf-Abwärtswandler (Boost-Buck) und Abwärtswandler (Buck) in Frage. Der high-seitige PWMTG-Treiber und die Low-EMI-Schalter lassen sich als Boost-, Buck- oder Boost-Buck-LED-Treiber konfigurieren, ohne dass dafür eines der wünschens-werten Features des IC (geringes EMI-Aufkommen, SSFM und eingebaute PWM-Dimmung) aufgegeben werden müsste. Als Boost-Wandler konfiguriert, kann der LT3922 LEDs mit bis

zu 34 V versorgen. Für Automotive-Anwendungen lässt er sich er als 400-kHz-Wandler (für maximalen Wirkungsgrad) oder als 2-MHz-Wandler (für minimale Abmessungen) mit einem PWM-Dimmungsbereich bis zu 5.000:1 konfigurieren. Die in Bild 3 gezeigte Boost-Buck-Konfiguration des LT3922 un-terstützt einen Eingangsspannungs-Bereich, der sich bis über und unter die LED-Stringspannung erstrecken kann. Die paten-tierte Low-EMI-Topologie besteht aus einem eingangsseitigen Aufwärtswandler mit geringer Welligkeit und einem ausgangssei-tigen Abwärtswandler mit ebenfalls geringer Welligkeit. Aus einer zwischen 4 V und 18 V liegenden Eingangsspannung lässt sich eine LED-Stringspannung von 3 V bis 16 V erzeugen.FazitDer LED-Treiber LT3922 wird den vielfältigen Anforderungen an LED-Treiber für Automotive- und Industrie-Anwendungen gerecht.

LINEAR TECHNOLOGY CORPORATION 2014

dn531f LT/AP 1014 111K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

Figure 2. Efficiency vs Load Current IOUT (VOUT = 25.2V) of the Converter in Figure 1

converter requiring only one inductor (L1). The propri-etary average current mode architecture uses two sense resistors (RCBRT1 and RCBRB1) to monitor the inductor current. In this buck-boost solution, when VIN is higher than VOUT, the converter operates in buck (step-down) mode; when VIN is lower than VOUT, the converter works at boost (step-up) mode. When VIN is close to VOUT, the converter operates in 4-switch buck-boost mode.

Figure 1) as a linear regulator, allowing the buck-boost converter output to rise above the battery voltage, while still providing charge current to the battery. This function is called PowerPath instant-on, when the PowerPath FET acts as a high impedance current source, providing charge current to the battery.

The LTC4020 automatically configures the PowerPath FET as an ideal diode when the battery charger is not in a charging cycle—namely, the buck-boost converter is operating exclusively for the system load. This allows the battery to remain disconnected from the converter output in normal operation. If, however, the system load current exceeds the buck-boost converter’s capacity, additional power can be efficiently drawn from the battery through this ideal diode.

Additional FeaturesThe LTC4020 supports timer-based charging algo-rithms—a capacitor from the TIMER pin to ground programs the end of the cycle time.

The LTC4020 features battery temperature monitor-ing and control. By connecting an NTC (negative temperature coefficient) thermistor to the NTC pin, and by placing the thermistor close to the battery pack (or other desired monitoring location), if the NTC pin voltage is out of range (above 1.35V or below 0.3V), the LTC4020 triggers an NTC fault and halts battery charging.

The LTC4020’s VIN_REG pin allows input voltage regula-tion. This pin can be used to program the peak power voltage for a solar panel, or help maintain a minimum voltage for other high impedance input supplies.

The LTC4020 has two open collector outputs, STAT1 and STAT2, to report charger status and fault condi-tions. These two pins are binary coded.

ConclusionThe LTC4020 is a versatile high voltage, high efficiency buck-boost power manager and multi-chemistry bat-tery charger, supporting input voltages above, below or equal to the output battery or system voltages. Its low profile (0.75mm) thermally enhanced 38-pin 5mm × 7mm QFN package is suitable for portable industrial and medical equipment, solar-powered systems, military communications equipment, and 12V to 24V embedded automotive systems.

Data Sheet Download

www.linear.com/LTC4020For applications help,

call (408) 432-1900, Ext. 3258

The converter operates at a programmable constant switching frequency within the range of 50kHz to 500kHz, set with a resistor (R13 = 100k, 250kHz). The solution shown in Figure 1 can supply up to 8A to the system load (VOUT = 25.2V). Figure 2 shows full load efficiency (IOUT = 8A, VIN = 24V) can reach above 98%.

The LTC4020 uses an external feedback resistor divider from the BAT pin to program battery volt-ages via the VFB pin. The PowerPath™ FET (M1) is on during normal battery charging, forming a low impedance connection between the battery and the buck-boost converter output when possible. Battery charge current is monitored through a sense resistor (RCBAT1). Maximum average battery charge current is easily programmed by selecting the value of RCBAT1. Dynamic current limit adjustment is possible through the RNG/SS pin.

Instant-On and Ideal Diode Functions with PowerPath FETFor a heavily discharged battery, the LTC4020 can automatically configure the PowerPath FET (M1 in

LOAD CURRENT (A)

EFFI

CIEN

CY (%

)

dn531 F02

0.1 1 10

100

90

70

50

80

60

40

30

15VIN, 25.2VOUT24VIN, 25.2VOUT55VIN, 25.2VOUT

MHz0

PEAK

RAD

IATE

D EM

I (dB

µV/m

)

50

40

30

20

10

0

–10400 800200 600

dn557 F02

1000

VIN = 14VVLED = 32VILED = 330mAf = 2MHz

CISPR 25, CLASS 5 LIMITSEMI DATANOISE FLOOR

VIN

VIN4V TO 18V

4.7µF

196k

53.6k

EN/UVLO

OVLO

VREF

PWM

CTRLANALOG DIMMING

SYNC/SPRDINTVCCFAULT

FAULT

BSTSW

VOUT

VOUT

FB FB

FB

RP VCRT

ISP

GND

ISN

PWMTGISMON

LT3922

499k

100k

100k

91k

100k

10k

0.1µF 1µF

470pF

1µF

L1A10µH

M1FERRITE BEADFB1

FERRITE BEADFB3

FERRITE BEADFB2

300mΩ

0.47µF50V

4.7µF25V

0.47µF50V

1µF

LED16V MAX330mA

LED–

LED+

SS

71.5k

332k122Hz

33nF

1µF

0.1µF 0.1µF0.1µF

2.2µF

D1: NXP PMEG4010CEJFB1, FB2: WÜRTH 742792097FB3: WÜRTH 742792040L1: WÜRTH 744877100 COUPLEDM1: VISHAY Si2319CDSQ1: ZETEX FMMT591AD2: OPT FOR LED-TO-GND SHORT PROTECTION

D1

OPTD2

ON

EXT PWM

INT

OFFSYNCEXT

INTVCC(SSFM ON)

EXT

SYNCPWMINT

PWMEXT OR ON

(RP DEFEAT)

100k

1MQ1

45.3k2MHz

L1B10µH

33µF50V

+

0.1µF

LINEAR TECHNOLOGY CORPORATION 2016

DN557 LT/AP 1216 71K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

Figure 3. 2MHz Boost-Buck LED Driver with Low Input and Output Ripple. Passes CISPR 25 Class 5 EMI

Built-In Features Enable Low EMIThe LT3922 includes a number of features that allow it to easily achieve low EMI. First, it incorporates Linear’s patented Silent Switcher architecture, where internal synchronous switches minimize hot-switching-loop size and controlled switching edges that do not ring. Its pinout enables placement of small, high frequency capacitors near the two VOUT pins to minimize hot-loop size and EMI. The switching edge rate is controlled by the IC, eliminating high frequency ringing that is common to converters without this feature, reduc-ing high frequency EMI without degrading power or efficiency.

SSFM in the LT3922 spreads the resistor-set switching frequency up and down from 100% to 125% of its value. This decreases both peak and average EMI in the converter at low and high frequencies.

Boost, Buck and Boost-BuckSince LEDs are light sources driven by controlled current, either or both of LED+ and LED– can be attached to non-ground potentials. This opens op-tions for LED driver topologies, including boost-buck (step-up and step-down) and buck mode (step-down). The high side PWMTG driver and low EMI switches can be configured as boost, buck, or boost-buck LED drivers while retaining use of all of the IC’s desirable features—low EMI, SSFM and internal PWM dimming.

The LT3922 can power LEDs up to 34V as a boost converter. For automotive applications it can be configured as a highest efficiency 400kHz converter or a smallest size 2MHz converter with up to 5000:1 PWM dimming range.

The LT3922 boost-buck topology in Figure 3 supports an input voltage range extending above and below the LED string voltage. This patented low EMI topology features a boost-type low ripple input inductor and a buck-type low ripple output-facing inductor. A 4V to 18V input can drive an LED string voltage between 3V and 16V.

ConclusionThe LT3922 synchronous LED driver meets the many demands of automotive and industrial LED drivers.

Data Sheet Download

www.linear.com/LT3922For applications help,

call (408) 432-1900, Ext. 3801

Figure 2. LT3922 Boost Passes CISPR 25 Class 5 Radiated and Conducted EMI

MHz0

PEAK

RAD

IATE

D EM

I (dB

µV/m

)

50

40

30

20

10

0

–10400 800200 600

dn557 F02

1000

VIN = 14VVLED = 32VILED = 330mAf = 2MHz

CISPR 25, CLASS 5 LIMITSEMI DATANOISE FLOOR

VIN

VIN4V TO 18V

4.7µF

196k

53.6k

EN/UVLO

OVLO

VREF

PWM

CTRLANALOG DIMMING

SYNC/SPRDINTVCCFAULT

FAULT

BSTSW

VOUT

VOUT

FB FB

FB

RP VCRT

ISP

GND

ISN

PWMTGISMON

LT3922

499k

100k

100k

91k

100k

10k

0.1µF 1µF

470pF

1µF

L1A10µH

M1FERRITE BEADFB1

FERRITE BEADFB3

FERRITE BEADFB2

300mΩ

0.47µF50V

4.7µF25V

0.47µF50V

1µF

LED16V MAX330mA

LED–

LED+

SS

71.5k

332k122Hz

33nF

1µF

0.1µF 0.1µF0.1µF

2.2µF

D1: NXP PMEG4010CEJFB1, FB2: WÜRTH 742792097FB3: WÜRTH 742792040L1: WÜRTH 744877100 COUPLEDM1: VISHAY Si2319CDSQ1: ZETEX FMMT591AD2: OPT FOR LED-TO-GND SHORT PROTECTION

D1

OPTD2

ON

EXT PWM

INT

OFFSYNCEXT

INTVCC(SSFM ON)

EXT

SYNCPWMINT

PWMEXT OR ON

(RP DEFEAT)

100k

1MQ1

45.3k2MHz

L1B10µH

33µF50V

+

0.1µF

LINEAR TECHNOLOGY CORPORATION 2016

DN557 LT/AP 1216 71K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

Figure 3. 2MHz Boost-Buck LED Driver with Low Input and Output Ripple. Passes CISPR 25 Class 5 EMI

Built-In Features Enable Low EMIThe LT3922 includes a number of features that allow it to easily achieve low EMI. First, it incorporates Linear’s patented Silent Switcher architecture, where internal synchronous switches minimize hot-switching-loop size and controlled switching edges that do not ring. Its pinout enables placement of small, high frequency capacitors near the two VOUT pins to minimize hot-loop size and EMI. The switching edge rate is controlled by the IC, eliminating high frequency ringing that is common to converters without this feature, reduc-ing high frequency EMI without degrading power or efficiency.

SSFM in the LT3922 spreads the resistor-set switching frequency up and down from 100% to 125% of its value. This decreases both peak and average EMI in the converter at low and high frequencies.

Boost, Buck and Boost-BuckSince LEDs are light sources driven by controlled current, either or both of LED+ and LED– can be attached to non-ground potentials. This opens op-tions for LED driver topologies, including boost-buck (step-up and step-down) and buck mode (step-down). The high side PWMTG driver and low EMI switches can be configured as boost, buck, or boost-buck LED drivers while retaining use of all of the IC’s desirable features—low EMI, SSFM and internal PWM dimming.

The LT3922 can power LEDs up to 34V as a boost converter. For automotive applications it can be configured as a highest efficiency 400kHz converter or a smallest size 2MHz converter with up to 5000:1 PWM dimming range.

The LT3922 boost-buck topology in Figure 3 supports an input voltage range extending above and below the LED string voltage. This patented low EMI topology features a boost-type low ripple input inductor and a buck-type low ripple output-facing inductor. A 4V to 18V input can drive an LED string voltage between 3V and 16V.

ConclusionThe LT3922 synchronous LED driver meets the many demands of automotive and industrial LED drivers.

Data Sheet Download

www.linear.com/LT3922For applications help,

call (408) 432-1900, Ext. 3801

Figure 2. LT3922 Boost Passes CISPR 25 Class 5 Radiated and Conducted EMI

MHz0

PEAK

RAD

IATE

D EM

I (dB

µV/m

)

50

40

30

20

10

0

–10400 800200 600

dn557 F02

1000

VIN = 14VVLED = 32VILED = 330mAf = 2MHz

CISPR 25, CLASS 5 LIMITSEMI DATANOISE FLOOR

VIN

VIN4V TO 18V

4.7µF

196k

53.6k

EN/UVLO

OVLO

VREF

PWM

CTRLANALOG DIMMING

SYNC/SPRDINTVCCFAULT

FAULT

BSTSW

VOUT

VOUT

FB FB

FB

RP VCRT

ISP

GND

ISN

PWMTGISMON

LT3922

499k

100k

100k

91k

100k

10k

0.1µF 1µF

470pF

1µF

L1A10µH

M1FERRITE BEADFB1

FERRITE BEADFB3

FERRITE BEADFB2

300mΩ

0.47µF50V

4.7µF25V

0.47µF50V

1µF

LED16V MAX330mA

LED–

LED+

SS

71.5k

332k122Hz

33nF

1µF

0.1µF 0.1µF0.1µF

2.2µF

D1: NXP PMEG4010CEJFB1, FB2: WÜRTH 742792097FB3: WÜRTH 742792040L1: WÜRTH 744877100 COUPLEDM1: VISHAY Si2319CDSQ1: ZETEX FMMT591AD2: OPT FOR LED-TO-GND SHORT PROTECTION

D1

OPTD2

ON

EXT PWM

INT

OFFSYNCEXT

INTVCC(SSFM ON)

EXT

SYNCPWMINT

PWMEXT OR ON

(RP DEFEAT)

100k

1MQ1

45.3k2MHz

L1B10µH

33µF50V

+

0.1µF

LINEAR TECHNOLOGY CORPORATION 2016

DN557 LT/AP 1216 71K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

Figure 3. 2MHz Boost-Buck LED Driver with Low Input and Output Ripple. Passes CISPR 25 Class 5 EMI

Built-In Features Enable Low EMIThe LT3922 includes a number of features that allow it to easily achieve low EMI. First, it incorporates Linear’s patented Silent Switcher architecture, where internal synchronous switches minimize hot-switching-loop size and controlled switching edges that do not ring. Its pinout enables placement of small, high frequency capacitors near the two VOUT pins to minimize hot-loop size and EMI. The switching edge rate is controlled by the IC, eliminating high frequency ringing that is common to converters without this feature, reduc-ing high frequency EMI without degrading power or efficiency.

SSFM in the LT3922 spreads the resistor-set switching frequency up and down from 100% to 125% of its value. This decreases both peak and average EMI in the converter at low and high frequencies.

Boost, Buck and Boost-BuckSince LEDs are light sources driven by controlled current, either or both of LED+ and LED– can be attached to non-ground potentials. This opens op-tions for LED driver topologies, including boost-buck (step-up and step-down) and buck mode (step-down). The high side PWMTG driver and low EMI switches can be configured as boost, buck, or boost-buck LED drivers while retaining use of all of the IC’s desirable features—low EMI, SSFM and internal PWM dimming.

The LT3922 can power LEDs up to 34V as a boost converter. For automotive applications it can be configured as a highest efficiency 400kHz converter or a smallest size 2MHz converter with up to 5000:1 PWM dimming range.

The LT3922 boost-buck topology in Figure 3 supports an input voltage range extending above and below the LED string voltage. This patented low EMI topology features a boost-type low ripple input inductor and a buck-type low ripple output-facing inductor. A 4V to 18V input can drive an LED string voltage between 3V and 16V.

ConclusionThe LT3922 synchronous LED driver meets the many demands of automotive and industrial LED drivers.

Data Sheet Download

www.linear.com/LT3922For applications help,

call (408) 432-1900, Ext. 3801

Figure 2. LT3922 Boost Passes CISPR 25 Class 5 Radiated and Conducted EMI

Bild 2. Der hier als Aufwärtswandler konfigurierte LT3922 erfüllt die Bedingungen von CISPR 25 Klasse 5 für leitungsgeführte und abgestrahlte Störaussendungen.

Bild 3. Dieser mit 2 MHz schaltende Auf-Abwärtswandler dient als LED-Treiber mit geringer Eingangs- und Ausgangswelligkeit und erfüllt die EMI-Anforderungen gemäß CISPR 25 Klasse 5.