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

06/17/563

EinführungEine neue Familie von Operationsverstärkern bietet ein bran-chenführendes Verhältnis zwischen Geschwindigkeit und Strom-aufnahme. Die Bausteine LTC6261 (Single), LTC6262 (Dual) und LTC6263 (Quad) kommen auf 30 MHz bei einer Stromaufnahme von nur 240 µA, zeichnen sich durch eine maximale Offsetspan-nung von 400 µV aus und bieten Rail-to-Rail-Ein- und Ausgänge. Mit ihrem Versorgungsspannungsbereich von 1,8 V bis 5,25 V eignen sich diese Operationsverstärker für Anwendungen, die nach kompromissloser Performance im Verbund mit geringer Stromaufnahme und niedriger Versorgungsspannung verlangen. Verstärker mit differenziellem Ausgang in Bridge-Tied-KonfigurationDie niedrige Stromaufnahme bei der gebotenen Bandbreite und die ausgezeichneten Rauscheigenschaften ermöglichen die Im-plementierung portabler Audio-Produkte, die bei einem Bruch-teil der sonst üblichen Leistungsaufnahme durch hervorragende Wiedergabetreue überzeugen. Angesichts der einzigartigen Fä-higkeiten des LTC6261 lohnt es sich, einen frischen Blick auf das Design von aktiven Filtern und Kopfhörerverstärkern zu werfen. Kopfhörerverstärker weisen Impedanzen zwischen 32 Ω und 300 Ω auf sowie eine Ansprechempfindlichkeit von 80 bis 100 dB SPL (SPL = Sound Pressure Level = Schalldruckpegel) pro Milliwatt

(mW) und mehr. Nimmt man als Beispiel einen Kopfhörerverstär-ker mit 90 dB SPL pro mW, so ist zum Erreichen von 110 dB SPL eine Leistung von 100 mW erforderlich. Bei einer Impedanz von 32 Ω ergibt sich ein RMS-Strom von 56 mA und eine Spannung von 1,8 V, während es bei 120 Ω 29 mA und 3,5 V sind. Legt man eine Versorgungsspannung von 3,3 V und den Ausgang eines Verstärkers vom Typ LTC6261 zugrunde, so reicht die ge-botene Treiberleistung unter Umständen nicht aus, um 100 mW zu erreichen. Zwei um 180° phasenversetzt betriebene Verstär-ker dagegen können die notwendige Treiberleistung aufbringen, um eine Leistung von über 100 mW abzugeben. Dupliziert man diesen Bridge-Tied-Treiber, so lassen sich der linke und der rechte Kanal versorgen. Der LTC6263 vereint vier Verstärker in einem Gehäuse. Die Daten eines aus zwei Verstärkern bestehenden LTC6262, mit dem ent-weder der rechte oder der linke Kanal angesteuert werden kann, sind in den Bildern 2 und 3 wiedergegeben. Die Grund-Stromauf-nahme der beiden Verstärker mit 1 VP-P am Eingang, aber ohne Last, beträgt 500 µA. Die Schaltung besteht aus einer invertierenden Verstärkerstufe

Low-Power-Operationsverstärker in stromsparenden Filtern und KopfhörertreibernDesign Note 563 Aaron Schultz

Bild 1: Kopfhörertreiber in Bridge-Tied-Konfiguration

–

+1/2 LTC6262

U2

C210µF R3

4.99k

C51nF

C3100pF

C4100pF

R84.99k

RSPEAKER120Ω

R64.7Ω

R210k

R94.7Ω

R110k

R715k

3V

VM

VINV1VIN VINV2NOISE FILTER

GAIN STAGE, OUTPUT DRIVE INVERSION STAGE, OUTPUT DRIVE

AC COUPLED INPUT

DN563 F01

–

+1/2 LTC6262

U1

3V

VM

Low Power Op Amp: Low Power Filter, Headphone Driver RevisitedDesign Note 563

by Aaron Schultz

IntroductionA new family of op amps features industry leading speed versus supply current. The LTC6261/LTC6262/ LTC6263 family (single, dual, quad) provides 30MHz at a low 240µA supply current, with 400µV maximum offset voltage and rail-to-rail input and output. In combination with 1.8V to 5.25V supply, these op amps enable applications requiring uncompromised performance with low power and low voltage.

Bridge-Tied Differential Output Amplifier The low supply current at the bandwidth and noise performance allows for excellent fidelity at a fraction of the usual dissipation in portable audio equipment. As with active filters, revisiting portable audio equip-ment headphone drivers is a rational enterprise, given the unique capabilities of the LTC6261.

Headphone speaker impedances range from 32Ω to 300Ω; their responsivity, from 80dB to 100dBSPL per 1mW and beyond. As an example, considering a headphone speaker with 90dBSPL per 1mW, it takes

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their respective owners.

100mW delivered to reach 110dBSPL. With 32Ω, the RMS current is 56mA and voltage 1.8V; with 120Ω, 29mA and 3.5V.

Given a 3.3V supply and the output of one LTC6261 amplifier, there may not be sufficient drive capabil-ity to yield 100mW. However, the combination of two 180° phased amplifiers is enough to provide the necessary drive to reach upwards of 100mW delivered power. Duplication of this bridge drive circuit enables power to both left and right sides.

The LTC6263 provides four amplifiers in one small package. Data from a 2-amplifier LTC6262 driving what could be left or right is shown in Figures 2 and 3. Basic current consumption of the two amplifiers, with as much as 1VP-P input but no load, is 500µA.

The circuit consists of first, an inverting gain stage with closed loop gain = 1.5, and a subsequent inverting stage. The combination of inverting stages produces a single-ended input to differential output gain of 3.

06/17/563

Figure 1. Audio Headphones Bridge Driver

–

+1/2 LTC6262

U2

C210µF R3

4.99k

C51nF

C3100pF

C4100pF

R84.99k

RSPEAKER120Ω

R64.7Ω

R210k

R94.7Ω

R110k

R715k

3V

VM

VINV1VIN VINV2NOISE FILTER

GAIN STAGE, OUTPUT DRIVE INVERSION STAGE, OUTPUT DRIVE

AC COUPLED INPUT

DN563 F01

–

+1/2 LTC6262

U1

3V

VM

Low Power Op Amp: Low Power Filter, Headphone Driver RevisitedDesign Note 563

by Aaron Schultz

IntroductionA new family of op amps features industry leading speed versus supply current. The LTC6261/LTC6262/ LTC6263 family (single, dual, quad) provides 30MHz at a low 240µA supply current, with 400µV maximum offset voltage and rail-to-rail input and output. In combination with 1.8V to 5.25V supply, these op amps enable applications requiring uncompromised performance with low power and low voltage.

Bridge-Tied Differential Output Amplifier The low supply current at the bandwidth and noise performance allows for excellent fidelity at a fraction of the usual dissipation in portable audio equipment. As with active filters, revisiting portable audio equip-ment headphone drivers is a rational enterprise, given the unique capabilities of the LTC6261.

Headphone speaker impedances range from 32Ω to 300Ω; their responsivity, from 80dB to 100dBSPL per 1mW and beyond. As an example, considering a headphone speaker with 90dBSPL per 1mW, it takes

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their respective owners.

100mW delivered to reach 110dBSPL. With 32Ω, the RMS current is 56mA and voltage 1.8V; with 120Ω, 29mA and 3.5V.

Given a 3.3V supply and the output of one LTC6261 amplifier, there may not be sufficient drive capabil-ity to yield 100mW. However, the combination of two 180° phased amplifiers is enough to provide the necessary drive to reach upwards of 100mW delivered power. Duplication of this bridge drive circuit enables power to both left and right sides.

The LTC6263 provides four amplifiers in one small package. Data from a 2-amplifier LTC6262 driving what could be left or right is shown in Figures 2 and 3. Basic current consumption of the two amplifiers, with as much as 1VP-P input but no load, is 500µA.

The circuit consists of first, an inverting gain stage with closed loop gain = 1.5, and a subsequent inverting stage. The combination of inverting stages produces a single-ended input to differential output gain of 3.

06/17/563

Figure 1. Audio Headphones Bridge Driver

–

+1/2 LTC6262

U2

C210µF R3

4.99k

C51nF

C3100pF

C4100pF

R84.99k

RSPEAKER120Ω

R64.7Ω

R210k

R94.7Ω

R110k

R715k

3V

VM

VINV1VIN VINV2NOISE FILTER

GAIN STAGE, OUTPUT DRIVE INVERSION STAGE, OUTPUT DRIVE

AC COUPLED INPUT

DN563 F01

–

+1/2 LTC6262

U1

3V

VM

Low Power Op Amp: Low Power Filter, Headphone Driver RevisitedDesign Note 563

by Aaron Schultz

IntroductionA new family of op amps features industry leading speed versus supply current. The LTC6261/LTC6262/ LTC6263 family (single, dual, quad) provides 30MHz at a low 240µA supply current, with 400µV maximum offset voltage and rail-to-rail input and output. In combination with 1.8V to 5.25V supply, these op amps enable applications requiring uncompromised performance with low power and low voltage.

Bridge-Tied Differential Output Amplifier The low supply current at the bandwidth and noise performance allows for excellent fidelity at a fraction of the usual dissipation in portable audio equipment. As with active filters, revisiting portable audio equip-ment headphone drivers is a rational enterprise, given the unique capabilities of the LTC6261.

Headphone speaker impedances range from 32Ω to 300Ω; their responsivity, from 80dB to 100dBSPL per 1mW and beyond. As an example, considering a headphone speaker with 90dBSPL per 1mW, it takes

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their respective owners.

100mW delivered to reach 110dBSPL. With 32Ω, the RMS current is 56mA and voltage 1.8V; with 120Ω, 29mA and 3.5V.

Given a 3.3V supply and the output of one LTC6261 amplifier, there may not be sufficient drive capabil-ity to yield 100mW. However, the combination of two 180° phased amplifiers is enough to provide the necessary drive to reach upwards of 100mW delivered power. Duplication of this bridge drive circuit enables power to both left and right sides.

The LTC6263 provides four amplifiers in one small package. Data from a 2-amplifier LTC6262 driving what could be left or right is shown in Figures 2 and 3. Basic current consumption of the two amplifiers, with as much as 1VP-P input but no load, is 500µA.

The circuit consists of first, an inverting gain stage with closed loop gain = 1.5, and a subsequent inverting stage. The combination of inverting stages produces a single-ended input to differential output gain of 3.

06/17/563

Figure 1. Audio Headphones Bridge Driver

Der MCB ist ein optionaler externer Crowbar-Baustein, der an den Ausgang angeschlossen wird. Sobald die Ausgangsspannung ei-nen einstellbaren Grenzwert überschreitet (voreingestellt ist eine Ansprechschwelle von 11 % über der Nennspannung), legt der LTM4641 seinen CROWBAR-Ausgang umgehend (d. h. mit einer Reaktionszeit von maximal 500 ns) auf logisch High und schaltet seine Ausgangsspannung dauerhaft ab. Die Leistungsstufe wird hochohmig, und der obere interne MOSFET wird ebenso wie der untere abgeschaltet. Der CROWBAR-Ausgang schaltet MCB ein, wodurch die Ausgangskondensatoren entladen werden und ein weiteres Ansteigen der Ausgangsspannung unterbunden wird. Der Baustein MSP ist zwischen die eingangsseitige Spannungs-quelle (VIN) und den Eingangs-Pin (VINH) der Leistungsstufe des LTM4641 geschaltet. Der Baustein dient als rückstellbarer elekt-ronischer Stromkreisunterbrecher. Sobald die internen Schaltun-gen des LTM4641 einen Fehler wie etwa eine Überspannung am Ausgang (Output Overvoltage – OOV) registrieren, wird das Gate des MSP in einer Zeitspanne von maximal 2,6 µs entladen, wo-durch der MSP abschaltet. Damit wird die Stromversorgung vom VINH-Anschluss, dem Eingang der Leistungsstufe des LTM4641, getrennt. Die gefährliche Eingangsspannung kann auf diese Weise nicht mehr an den wertvollen Verbraucher gelangen. Zur Erzeugung des OOV-Grenzwerts nutzt der LTM4641 ferner eine unabhängige Referenzspannung, die nicht mit der Bandlücken (bandgap) -Spannung des Regelungs-IC zusammenhängt.

Bild 1 zeigt den Verlauf der CROWBAR-Spannung und von VOUT, wenn der obere MOSFET (MTOP) ausfällt und es zu einem Kurz-schluss zwischen VIN und dem Knoten SW kommt. Das CROW-BAR-Signal wechselt binnen 500 ns in den High-Status und schaltet damit den MCB ein, der den Ausgang mit der Masse verbindet. VOUT steigt zu keinem Zeitpunkt auf mehr als 110 % der Nenn-Ausgangsspannung an. Über- und Unterspannungsschutz für den EingangDer Eingang des LTM4641 ist mit einem Über- und Unterspan-nungsschutz versehen, dessen Ansprechschwellen vom Benutzer gewählt werden können (Bild 2). Der UVLO-Pin (UVLO = Undervoltage-Lockout) ist direkt mit dem invertierenden Eingang eines Komparators verbunden, dessen Ansprechschwelle 0,5 V beträgt. Wenn die Spannung am UVLO-Pin auf unter 0,5 V fällt, wird das Schalten des Wandlers unter-bunden. Sobald die Spannung an UVLO wieder über 0,5 V ansteigt, kann das Schalten wieder beginnen. Die Pins IOVRETRY und OVLO sind direkt an die nicht invertierenden Eingänge von Komparato-ren geführt, deren Ansprechschwellen ebenfalls 0,5 V betragen. Steigt die Spannung am Pin IOVRETRY auf über 0,5 V an, so wird das Schalten des Wandlers ebenfalls unterbrochen. Erst wenn die Spannung an IOVRETRY wieder mehr als 0,5 V beträgt, wird das Schalten wieder freigegeben. Das Schalten des Wandlers wird auch dann unterbunden, wenn die Spannung an OVLO die Marke

von 0,5 V übersteigt. Fällt die Spannung anschließend wieder un-ter 0,5 V, wird das Schalten jedoch erst dann wieder ermöglicht, wenn das Latch zurückgesetzt wurde. Diese drei Pins bieten zu-sätzliche Flexibilität, um das Verhalten des LTM4641 individuell einzustellen.

LINEAR TECHNOLOGY CORPORATION 2014

dn527 LT/AP 0614 111K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com

Figure 3. Efficiency Curves of LTM4641

Data Sheet Download

www.linear.com/LTM4641For applications help,

call (408) 432-1900, Ext. 3979

MCB is an external optional crowbar device residing on VOUT. If the output voltage exceeds an adjustable threshold —default value is 11% above nominal— the LTM4641 pulls its CROWBAR output logic high immediately (500ns response time, maximum) and latches off its output voltage: the power stage becomes high impedance, with both internal top and bottom MOSFETs latched off. The CROWBAR output turns on MCB, discharging the output capacitors and preventing any further positive excursion of the output voltage.

MSP is placed between the input power source (VIN) and the LTM4641's power stage input pins (VINH), and is used as a resettable electronic power-interrupt switch. When a fault condition, such as an output overvoltage (OOV) condition, is detected by the LTM4641’s internal circuitry, the gate of MSP is discharged within 2.6μs (maximum) and MSP turns off. The input source sup-ply is thus disconnected from the LTM4641’s power stage input (VINH), preventing the hazardous (input) voltage from reaching the precious load. LTM4641 also uses an independent reference voltage to gener-ate an OOV threshold, separate from the control IC’s bandgap voltage.

Figure 1 shows the CROWBAR and VOUT waveforms when the top MOSFET MTOP fails, causing a short-circuit between the VIN and SW nodes. CROWBAR goes high within 500ns and turns on MCB to short the output to ground. VOUT never exceeds 110% of the specified output voltage.

Input Overvoltage and Undervoltage ProtectionsThe LTM4641 has input undervoltage and overvoltage protections, whose trip thresholds can be set by the user. Please refer to Figure 2.

The UVLO pin feeds directly into the inverting input of a comparator whose trip threshold is 0.5V. When the UVLO pin falls below 0.5V, switching action is inhibited; when the UVLO pin exceeds 0.5V, switching action can resume. The IOVRETRY and OVLO pins each feed directly into noninverting inputs of comparators whose trip thresholds are 0.5V. When the IOVRETRY pin exceeds 0.5V, switching action is inhibited; when IOVRETRY falls below 0.5V, switching action can resume. When the OVLO pin exceeds 0.5V, switching action is inhibited; when OVLO subsequently falls below 0.5V, switching action cannot occur until the latch has

been reset. These three pins give added flexibility to tailor the behavior of the LTM4641.

Figure 2. Circuit to Set the Input UVLO, IOVRETRY and OVLO Thresholds

+

VINLVINH

LTM4641UVLO

UVLO < 0.5V = OFF

HYST PULLS UP WHENON, HYST PULLS DOWN

WHEN OFF

HYST

IOVRETRYIOVRETRY > 0.5V = OFF

OVLO > 0.5V = LATCHOFFOVLO

SGND GND

AN527 F02

RTUV

CIN(MLCC)10µF×2

CIN(BULK)

VIN

RBUV

RTOV

RMOV

RBOV

RHYST

SGND CONNECTS TO GND INTERNAL TO MODULE. KEEP SGND ROUTES/PLANES SEPARATE FROM GNDON MOTHERBOARD

EfficiencyFigure 3 below shows the efficiency curves for the LTM4641 for a typical 12V input voltage for the circuit in Figure 1. With all the protection circuits, LTM4641 can still achieve high efficiency.

ConclusionThe LTM4641 μModule regulator monitors input voltage, output voltage and temperature conditions. It can provide comprehensive electrical and thermal protection from excessive voltage stress for loads such as processors, ASICs and high end FPGAs.

OUTPUT CURRENT (A)0

EFFI

CIEN

CY (%

)

95

85

70

90

80

75

65

604 82 6

DN527 F03

1093 71 5

6.0VOUT5.0VOUT3.3VOUT2.5VOUT1.8VOUT1.5VOUT1.2VOUT1.0VOUT0.9VOUT

Bild 2. Beschaltung zum Festlegen der Ansprechschwellen für UVLO, IOVRETRY und OVLO

EffizienzBild 3 zeigt die typischen Wirkungsgradkurven des LTM4641 bei einer typischen Eingangsspannung von 12 V für die Schaltung aus Bild 1. Auch mit allen Schutzschaltungen kommt der LTM4641 auf eine hohe Effizienz.

LINEAR TECHNOLOGY CORPORATION 2014

dn527 LT/AP 0614 111K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com

Figure 3. Efficiency Curves of LTM4641

Data Sheet Download

www.linear.com/LTM4641For applications help,

call (408) 432-1900, Ext. 3979

MCB is an external optional crowbar device residing on VOUT. If the output voltage exceeds an adjustable threshold —default value is 11% above nominal— the LTM4641 pulls its CROWBAR output logic high immediately (500ns response time, maximum) and latches off its output voltage: the power stage becomes high impedance, with both internal top and bottom MOSFETs latched off. The CROWBAR output turns on MCB, discharging the output capacitors and preventing any further positive excursion of the output voltage.

MSP is placed between the input power source (VIN) and the LTM4641's power stage input pins (VINH), and is used as a resettable electronic power-interrupt switch. When a fault condition, such as an output overvoltage (OOV) condition, is detected by the LTM4641’s internal circuitry, the gate of MSP is discharged within 2.6μs (maximum) and MSP turns off. The input source sup-ply is thus disconnected from the LTM4641’s power stage input (VINH), preventing the hazardous (input) voltage from reaching the precious load. LTM4641 also uses an independent reference voltage to gener-ate an OOV threshold, separate from the control IC’s bandgap voltage.

Figure 1 shows the CROWBAR and VOUT waveforms when the top MOSFET MTOP fails, causing a short-circuit between the VIN and SW nodes. CROWBAR goes high within 500ns and turns on MCB to short the output to ground. VOUT never exceeds 110% of the specified output voltage.

Input Overvoltage and Undervoltage ProtectionsThe LTM4641 has input undervoltage and overvoltage protections, whose trip thresholds can be set by the user. Please refer to Figure 2.

The UVLO pin feeds directly into the inverting input of a comparator whose trip threshold is 0.5V. When the UVLO pin falls below 0.5V, switching action is inhibited; when the UVLO pin exceeds 0.5V, switching action can resume. The IOVRETRY and OVLO pins each feed directly into noninverting inputs of comparators whose trip thresholds are 0.5V. When the IOVRETRY pin exceeds 0.5V, switching action is inhibited; when IOVRETRY falls below 0.5V, switching action can resume. When the OVLO pin exceeds 0.5V, switching action is inhibited; when OVLO subsequently falls below 0.5V, switching action cannot occur until the latch has

been reset. These three pins give added flexibility to tailor the behavior of the LTM4641.

Figure 2. Circuit to Set the Input UVLO, IOVRETRY and OVLO Thresholds

+

VINLVINH

LTM4641UVLO

UVLO < 0.5V = OFF

HYST PULLS UP WHENON, HYST PULLS DOWN

WHEN OFF

HYST

IOVRETRYIOVRETRY > 0.5V = OFF

OVLO > 0.5V = LATCHOFFOVLO

SGND GND

AN527 F02

RTUV

CIN(MLCC)10µF×2

CIN(BULK)

VIN

RBUV

RTOV

RMOV

RBOV

RHYST

SGND CONNECTS TO GND INTERNAL TO MODULE. KEEP SGND ROUTES/PLANES SEPARATE FROM GNDON MOTHERBOARD

EfficiencyFigure 3 below shows the efficiency curves for the LTM4641 for a typical 12V input voltage for the circuit in Figure 1. With all the protection circuits, LTM4641 can still achieve high efficiency.

ConclusionThe LTM4641 μModule regulator monitors input voltage, output voltage and temperature conditions. It can provide comprehensive electrical and thermal protection from excessive voltage stress for loads such as processors, ASICs and high end FPGAs.

OUTPUT CURRENT (A)0

EFFI

CIEN

CY (%

)

95

85

70

90

80

75

65

604 82 6

DN527 F03

1093 71 5

6.0VOUT5.0VOUT3.3VOUT2.5VOUT1.8VOUT1.5VOUT1.2VOUT1.0VOUT0.9VOUT

Bild 3. Wirkungsgrad-Kennlinien des LTM4641FazitDas µModule LTM4641 überwacht die Eingangsspannung, die Ausgangsspannung und die Temperaturbedingungen. Der Bau-stein bietet Verbrauchern wie etwa Prozessoren, ASICs und an-spruchsvollen FPGAs einen umfassenden elektrischen und ther-mischen Schutz vor überhöhten Spannungen.

LINEAR TECHNOLOGY CORPORATION 2014

dn527 LT/AP 0614 111K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com

Figure 3. Efficiency Curves of LTM4641

Data Sheet Download

www.linear.com/LTM4641For applications help,

call (408) 432-1900, Ext. 3979

MCB is an external optional crowbar device residing on VOUT. If the output voltage exceeds an adjustable threshold —default value is 11% above nominal— the LTM4641 pulls its CROWBAR output logic high immediately (500ns response time, maximum) and latches off its output voltage: the power stage becomes high impedance, with both internal top and bottom MOSFETs latched off. The CROWBAR output turns on MCB, discharging the output capacitors and preventing any further positive excursion of the output voltage.

MSP is placed between the input power source (VIN) and the LTM4641's power stage input pins (VINH), and is used as a resettable electronic power-interrupt switch. When a fault condition, such as an output overvoltage (OOV) condition, is detected by the LTM4641’s internal circuitry, the gate of MSP is discharged within 2.6μs (maximum) and MSP turns off. The input source sup-ply is thus disconnected from the LTM4641’s power stage input (VINH), preventing the hazardous (input) voltage from reaching the precious load. LTM4641 also uses an independent reference voltage to gener-ate an OOV threshold, separate from the control IC’s bandgap voltage.

Figure 1 shows the CROWBAR and VOUT waveforms when the top MOSFET MTOP fails, causing a short-circuit between the VIN and SW nodes. CROWBAR goes high within 500ns and turns on MCB to short the output to ground. VOUT never exceeds 110% of the specified output voltage.

Input Overvoltage and Undervoltage ProtectionsThe LTM4641 has input undervoltage and overvoltage protections, whose trip thresholds can be set by the user. Please refer to Figure 2.

The UVLO pin feeds directly into the inverting input of a comparator whose trip threshold is 0.5V. When the UVLO pin falls below 0.5V, switching action is inhibited; when the UVLO pin exceeds 0.5V, switching action can resume. The IOVRETRY and OVLO pins each feed directly into noninverting inputs of comparators whose trip thresholds are 0.5V. When the IOVRETRY pin exceeds 0.5V, switching action is inhibited; when IOVRETRY falls below 0.5V, switching action can resume. When the OVLO pin exceeds 0.5V, switching action is inhibited; when OVLO subsequently falls below 0.5V, switching action cannot occur until the latch has

been reset. These three pins give added flexibility to tailor the behavior of the LTM4641.

Figure 2. Circuit to Set the Input UVLO, IOVRETRY and OVLO Thresholds

+

VINLVINH

LTM4641UVLO

UVLO < 0.5V = OFF

HYST PULLS UP WHENON, HYST PULLS DOWN

WHEN OFF

HYST

IOVRETRYIOVRETRY > 0.5V = OFF

OVLO > 0.5V = LATCHOFFOVLO

SGND GND

AN527 F02

RTUV

CIN(MLCC)10µF×2

CIN(BULK)

VIN

RBUV

RTOV

RMOV

RBOV

RHYST

SGND CONNECTS TO GND INTERNAL TO MODULE. KEEP SGND ROUTES/PLANES SEPARATE FROM GNDON MOTHERBOARD

EfficiencyFigure 3 below shows the efficiency curves for the LTM4641 for a typical 12V input voltage for the circuit in Figure 1. With all the protection circuits, LTM4641 can still achieve high efficiency.

ConclusionThe LTM4641 μModule regulator monitors input voltage, output voltage and temperature conditions. It can provide comprehensive electrical and thermal protection from excessive voltage stress for loads such as processors, ASICs and high end FPGAs.

OUTPUT CURRENT (A)0

EFFI

CIEN

CY (%

)

95

85

70

90

80

75

65

604 82 6

DN527 F03

1093 71 5

6.0VOUT5.0VOUT3.3VOUT2.5VOUT1.8VOUT1.5VOUT1.2VOUT1.0VOUT0.9VOUT

LINEAR TECHNOLOGY CORPORATION 2014

dn527 LT/AP 0614 111K • PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com

Figure 3. Efficiency Curves of LTM4641

Data Sheet Download

www.linear.com/LTM4641For applications help,

call (408) 432-1900, Ext. 3979

MCB is an external optional crowbar device residing on VOUT. If the output voltage exceeds an adjustable threshold —default value is 11% above nominal— the LTM4641 pulls its CROWBAR output logic high immediately (500ns response time, maximum) and latches off its output voltage: the power stage becomes high impedance, with both internal top and bottom MOSFETs latched off. The CROWBAR output turns on MCB, discharging the output capacitors and preventing any further positive excursion of the output voltage.

MSP is placed between the input power source (VIN) and the LTM4641's power stage input pins (VINH), and is used as a resettable electronic power-interrupt switch. When a fault condition, such as an output overvoltage (OOV) condition, is detected by the LTM4641’s internal circuitry, the gate of MSP is discharged within 2.6μs (maximum) and MSP turns off. The input source sup-ply is thus disconnected from the LTM4641’s power stage input (VINH), preventing the hazardous (input) voltage from reaching the precious load. LTM4641 also uses an independent reference voltage to gener-ate an OOV threshold, separate from the control IC’s bandgap voltage.

Figure 1 shows the CROWBAR and VOUT waveforms when the top MOSFET MTOP fails, causing a short-circuit between the VIN and SW nodes. CROWBAR goes high within 500ns and turns on MCB to short the output to ground. VOUT never exceeds 110% of the specified output voltage.

Input Overvoltage and Undervoltage ProtectionsThe LTM4641 has input undervoltage and overvoltage protections, whose trip thresholds can be set by the user. Please refer to Figure 2.

The UVLO pin feeds directly into the inverting input of a comparator whose trip threshold is 0.5V. When the UVLO pin falls below 0.5V, switching action is inhibited; when the UVLO pin exceeds 0.5V, switching action can resume. The IOVRETRY and OVLO pins each feed directly into noninverting inputs of comparators whose trip thresholds are 0.5V. When the IOVRETRY pin exceeds 0.5V, switching action is inhibited; when IOVRETRY falls below 0.5V, switching action can resume. When the OVLO pin exceeds 0.5V, switching action is inhibited; when OVLO subsequently falls below 0.5V, switching action cannot occur until the latch has

been reset. These three pins give added flexibility to tailor the behavior of the LTM4641.

Figure 2. Circuit to Set the Input UVLO, IOVRETRY and OVLO Thresholds

+

VINLVINH

LTM4641UVLO

UVLO < 0.5V = OFF

HYST PULLS UP WHENON, HYST PULLS DOWN

WHEN OFF

HYST

IOVRETRYIOVRETRY > 0.5V = OFF

OVLO > 0.5V = LATCHOFFOVLO

SGND GND

AN527 F02

RTUV

CIN(MLCC)10µF×2

CIN(BULK)

VIN

RBUV

RTOV

RMOV

RBOV

RHYST

SGND CONNECTS TO GND INTERNAL TO MODULE. KEEP SGND ROUTES/PLANES SEPARATE FROM GNDON MOTHERBOARD

EfficiencyFigure 3 below shows the efficiency curves for the LTM4641 for a typical 12V input voltage for the circuit in Figure 1. With all the protection circuits, LTM4641 can still achieve high efficiency.

ConclusionThe LTM4641 μModule regulator monitors input voltage, output voltage and temperature conditions. It can provide comprehensive electrical and thermal protection from excessive voltage stress for loads such as processors, ASICs and high end FPGAs.

OUTPUT CURRENT (A)0

EFFI

CIEN

CY (%

)

95

85

70

90

80

75

65

604 82 6

DN527 F03

1093 71 5

6.0VOUT5.0VOUT3.3VOUT2.5VOUT1.8VOUT1.5VOUT1.2VOUT1.0VOUT0.9VOUT

Bei technischen Fragen,Telefon +49 89 96 24 55 0www.linear.com/LTC6261

mit einer geschlossenen Schleifenverstärkung von 1,5 und einer weiteren invertierenden Stufe. Beide invertierenden Stufen ge-meinsam bewirken eine Verstärkung von 3 zwischen dem mas-sebezogenen Eingang und dem differenziellen Ausgang. Bei 500 mVP-P am Eingang liegen am Ausgang 1,5 VP-P oder 0,75 V max. bzw. 0,53 VRMS. Bei 50 Ω führen 500 mV am Ein-gang zu einer Leistungsabgabe von rund 5,6 mW. Bei 1 VP-P am Eingang liefert die Schaltung bereits 22,5 mW. Hilfreich ist hier der Rail-to-Rail-Ausgang des LTC6261. Beim ersten Laboraufbau dieser Schaltung entstand ein starker Ton mit einer Frequenz von einigen hundert Kilohertz. Wie sich herausstellte, war der positive Eingang nicht einwandfrei als ‚AC-Masse‘ über alle Frequenzen hinweg mit Masse verbunden, da die Spannung nicht fest verankert war. Die Notwendigkeit zum Festlegen der Spannung entsteht, wenn anstelle einer bi-polaren Versorgungsspannung eine unipolare verwendet wird. In diesem Fall nämlich liegt VM nicht auf Massepotenzial, sondern weist eine zwischen den beiden anderen liegende Spannung auf, die eine einwandfreie Funktion der invertierenden Topologien ermöglichen soll. Der Widerstandsteiler zur Erzeugung von VM weist hohe Widerstandswerte auf (z. B. zweimal 470 kΩ in Serie), um die Zunahme der Stromaufnahme zu minimieren. Ein großer Kondensator gewährleistet eine wirkungsvolle Masseverbindung bei niedrigen Frequenzen. Tatsächlich sorgte das Hinzufügen eines großen Kondensators von 1 µF, der zusammen mit den 470-kΩ-Widerständen eine Polstelle bildet, für die Beseitigung des mysteriösen Störtons.

Ungeachtet der geringen Stromaufnahme steuert dieser Treiber einen angeschlossenen Kopfhörer mit geringer Verzerrung an. Bei genügend hoher Amplitude allerdings nehmen die Verzerrun-gen dramatisch zu, weil das Ausgangssignal des Operationsver-stärkers gekappt wird. Dieses Phänomen tritt mit zunehmender Last immer früher auf, da die Stromverstärkung der Ausgangs-transistoren dann nicht mehr ausreicht. Ein wichtiges Kriterium bei tragbaren Geräten ist die Stroment-nahme aus der Batterie, die je nach der Lautstärke und dem Musikgeschmack des Zuhörers unterschiedlich stark ist. Wie ein Gerät letztendlich eingesetzt wird, liegt außerhalb der Kontrolle des Designers. Anders ist es mit der Ruhestromaufnahme. Da sich das Gerät möglicherweise zu einem Großteil der Zeit im Leerlaufstatus befindet, fällt die Ruhestromaufnahme durchaus ins Gewicht, da das System der Batterie ständig einen Strom entnimmt. Die niedrige Ruhestromaufnahme des LTC6261 sorgt somit dafür, dass die Batterie länger hält.FazitDie hier gezeigten Anwendungen profitieren von der einzig-artigen Feature-Kombination der Operationsverstärkerfamilie LTC6261. Die geringe Ruhestromaufnahme dieser Bauelemen-te geht nicht zulasten ihrer Leistungsfähigkeit in Regionen, die sonst Bauelementen mit mehr Strombedarf vorbehalten sind. Die Rail-to-Rail-Ein- und Ausgänge, die Shutdown-Funktion und die Auswahl unter verschiedenen Gehäusen kommen der Vielseitig-keit der Familie zusätzlich zugute.

INPUT = 500mVP-P

FREQUENCY (kHz)0.1 1 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

THD

+ NO

ISE

(%)

DN563 F02

50Ω100Ω300ΩNO LOAD INPUT AT 1kHz

NO LOAD300Ω100Ω50Ω

AUDIO INPUT AMPLITUDE (V)0.001 0.01 0.1 1 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

THD

+ NO

ISE

(%)

DN563 F03

Data Sheet Download

www.linear.com/LTC6261For applications help,

call (408) 432-1900, Ext. 3409

With 500mVP-P input, the output is 1.5VP-P, or 0.75V max, or 0.53VRMS. With 50Ω, 500mV input leads to approximately 5.6mW delivered power. At 1VP-P input, the circuit delivers 22.5mW. Note that it helps that the LTC6261 output can swing close to rail-to-rail with load.

The first build of this circuit in the lab produced a significant tone at a few hundred Hz. It turned out that the positive input was not well grounded as an “AC ground” over all frequencies because the voltage was not strongly pegged. The need to peg the voltage arises when using a single supply rather than a dual supply. With a single supply, VM is not ground, but rather a mid-rail voltage created to enable inverting topologies to work properly. The resistor divider that creates VM has large resistance values (for example, two 470k in series) to minimize additional supply cur-rent. A large capacitor ensures a strong ground at low frequencies. Indeed, the addition of a large capacitor (1µF, which forms a pole with the 470k resistors in parallel) eliminated the mysterious distortion tone.

Figure 2. LTC6262 Bridge Driver THD and Noise with Different Loads vs Frequency

Figure 3. LTC6262 Bridge Driver THD and Noise with Different Loads vs Amplitude at 1kHz

Despite the low quiescent current, this driver delivers low distortion to a headphone load. At high enough amplitude, distortion increases dramatically as the op amp output clips. Clipping occurs sooner with more loading as the output transistors start to run out of current gain.

One significant concern in a portable device is bat-tery drain. Music played loudly, or listeners’ musical choices affect the rate of battery drain. The end-use of a device is out of the designer’s control. Quiescent current, though, is not. Because much of a device’s time may be spent idle, quiescent current is significant, as it drains batteries continuously. The LTC6261’s low quiescent current increases battery discharge time.

ConclusionThe applications shown here take advantage of a unique combination of features available in the LTC6261 op amp family. The low quiescent current of these devices does not diminish their ability to perform at levels usually reserved for more power hungry parts. Rail-to-rail input and output, shutdown, and choice of package are features that add to their versatility.

DN563 LT/TP 0617 71K • PRINTED IN THE USA© LINEAR TECHNOLOGY CORPORATION 2017

INPUT = 500mVP-P

FREQUENCY (kHz)0.1 1 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

THD

+ NO

ISE

(%)

DN563 F02

50Ω100Ω300ΩNO LOAD INPUT AT 1kHz

NO LOAD300Ω100Ω50Ω

AUDIO INPUT AMPLITUDE (V)0.001 0.01 0.1 1 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

THD

+ NO

ISE

(%)

DN563 F03

Data Sheet Download

www.linear.com/LTC6261For applications help,

call (408) 432-1900, Ext. 3409

With 500mVP-P input, the output is 1.5VP-P, or 0.75V max, or 0.53VRMS. With 50Ω, 500mV input leads to approximately 5.6mW delivered power. At 1VP-P input, the circuit delivers 22.5mW. Note that it helps that the LTC6261 output can swing close to rail-to-rail with load.

The first build of this circuit in the lab produced a significant tone at a few hundred Hz. It turned out that the positive input was not well grounded as an “AC ground” over all frequencies because the voltage was not strongly pegged. The need to peg the voltage arises when using a single supply rather than a dual supply. With a single supply, VM is not ground, but rather a mid-rail voltage created to enable inverting topologies to work properly. The resistor divider that creates VM has large resistance values (for example, two 470k in series) to minimize additional supply cur-rent. A large capacitor ensures a strong ground at low frequencies. Indeed, the addition of a large capacitor (1µF, which forms a pole with the 470k resistors in parallel) eliminated the mysterious distortion tone.

Figure 2. LTC6262 Bridge Driver THD and Noise with Different Loads vs Frequency

Figure 3. LTC6262 Bridge Driver THD and Noise with Different Loads vs Amplitude at 1kHz

Despite the low quiescent current, this driver delivers low distortion to a headphone load. At high enough amplitude, distortion increases dramatically as the op amp output clips. Clipping occurs sooner with more loading as the output transistors start to run out of current gain.

One significant concern in a portable device is bat-tery drain. Music played loudly, or listeners’ musical choices affect the rate of battery drain. The end-use of a device is out of the designer’s control. Quiescent current, though, is not. Because much of a device’s time may be spent idle, quiescent current is significant, as it drains batteries continuously. The LTC6261’s low quiescent current increases battery discharge time.

ConclusionThe applications shown here take advantage of a unique combination of features available in the LTC6261 op amp family. The low quiescent current of these devices does not diminish their ability to perform at levels usually reserved for more power hungry parts. Rail-to-rail input and output, shutdown, and choice of package are features that add to their versatility.

DN563 LT/TP 0617 71K • PRINTED IN THE USA© LINEAR TECHNOLOGY CORPORATION 2017

INPUT = 500mVP-P

FREQUENCY (kHz)0.1 1 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

THD

+ NO

ISE

(%)

DN563 F02

50Ω100Ω300ΩNO LOAD INPUT AT 1kHz

NO LOAD300Ω100Ω50Ω

AUDIO INPUT AMPLITUDE (V)0.001 0.01 0.1 1 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

THD

+ NO

ISE

(%)

DN563 F03

Data Sheet Download

www.linear.com/LTC6261For applications help,

call (408) 432-1900, Ext. 3409

With 500mVP-P input, the output is 1.5VP-P, or 0.75V max, or 0.53VRMS. With 50Ω, 500mV input leads to approximately 5.6mW delivered power. At 1VP-P input, the circuit delivers 22.5mW. Note that it helps that the LTC6261 output can swing close to rail-to-rail with load.

The first build of this circuit in the lab produced a significant tone at a few hundred Hz. It turned out that the positive input was not well grounded as an “AC ground” over all frequencies because the voltage was not strongly pegged. The need to peg the voltage arises when using a single supply rather than a dual supply. With a single supply, VM is not ground, but rather a mid-rail voltage created to enable inverting topologies to work properly. The resistor divider that creates VM has large resistance values (for example, two 470k in series) to minimize additional supply cur-rent. A large capacitor ensures a strong ground at low frequencies. Indeed, the addition of a large capacitor (1µF, which forms a pole with the 470k resistors in parallel) eliminated the mysterious distortion tone.

Figure 2. LTC6262 Bridge Driver THD and Noise with Different Loads vs Frequency

Figure 3. LTC6262 Bridge Driver THD and Noise with Different Loads vs Amplitude at 1kHz

Despite the low quiescent current, this driver delivers low distortion to a headphone load. At high enough amplitude, distortion increases dramatically as the op amp output clips. Clipping occurs sooner with more loading as the output transistors start to run out of current gain.

One significant concern in a portable device is bat-tery drain. Music played loudly, or listeners’ musical choices affect the rate of battery drain. The end-use of a device is out of the designer’s control. Quiescent current, though, is not. Because much of a device’s time may be spent idle, quiescent current is significant, as it drains batteries continuously. The LTC6261’s low quiescent current increases battery discharge time.

ConclusionThe applications shown here take advantage of a unique combination of features available in the LTC6261 op amp family. The low quiescent current of these devices does not diminish their ability to perform at levels usually reserved for more power hungry parts. Rail-to-rail input and output, shutdown, and choice of package are features that add to their versatility.

DN563 LT/TP 0617 71K • PRINTED IN THE USA© LINEAR TECHNOLOGY CORPORATION 2017

Bild 2: THD und Rauschen des Bridge-Tied-Treibers LTC6262 bei verschiedenen Lasten als Funktion der

Frequenz

Bild 3: THD und Rauschen des Bridge-Tied-Treibers LTC6262 bei 1 kHz und verschiedenen Lasten als Funktion

der Amplitude