LM5007_08资料

LM5007 High Voltage (80V) Step Down Switching RegulatorFebruary 5, 2008

LM5007

High Voltage (80V) Step Down Switching Regulator

General Description

The LM5007 Step Down Switching Regulator features all ofthe functions needed to implement low cost, efficient, Buckbias regulators. This high voltage regulator contains an 80 V,0.7A N-Channel Buck Switch. The device is easy to apply andis provided in the MSOP-8 and the thermally enhanced LLP-8packages. The regulator is based on a hysteretic controlscheme using an on time inversely proportional to VIN. Thisfeature allows the operating frequency to remain relativelyconstant with load and input voltage variations. The hystereticcontrol requires no control loop compensation, while provid-ing very fast load transient response. An intelligent currentlimit is implemented in the LM5007 with forced off time that isinversely proportional to VOUT. This current limiting schemereduces load current foldback. Additional protection featuresinclude: Thermal Shutdown, Vcc undervoltage lockout, gatedrive undervoltage lockout, and Max Duty Cycle limiter.

Features

■■■■■■■■■■■■■

Integrated 80V, 0.7A N-Channel Buck SwitchInternal HV Vcc Regulator

No Control Loop Compensation RequiredUltra-Fast Transient Response

On Time Varies Inversely with Line Voltage

Operating Frequency Nearly Constant with Varying LineVoltage

Adjustable Output VoltageHighly Efficient OperationPrecision ReferenceLow Bias Current

Intelligent Current Limit ProtectionThermal Shutdown

External Shutdown Control

Typical Applications

■Non-Isolated Buck Regulator

■Secondary High Voltage Post Regulator■+42V Automotive Systems

Package

■MSOP - 8

■LLP - 8 (4mm x 4mm)

Connection Diagram

8-Lead MSOP, LLP

20078302

Ordering Information

Order NumberLM5007MMLM5007MMXLM5007SDLM5007SDX

Package TypeMSOP-8MSOP-8LLP-8LLP-8

NSC Package Drawing

MUA08AMUA08ASDC08ASDC08A

Supplied As

1000 Units on Tape and Reel3500 Units on Tape and Reel1000 Units on Tape and Reel4500 Units on Tape and Reel

© 2008 National Semiconductor Corporation200783www.national.com

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LM5007Typical Application Circuit and Block Diagram

20078301

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LM5007Pin Descriptions

Pin12

NameSWBST

Switching Node

Boost Boot–strap capacitor input

Description

Application Information

Power switching node. Connect to the LC output filter.An external capacitor is required between the BSTand the SW pins. A 0.01uF ceramic capacitor isrecommended. An internal diode between Vcc andBST completes the Buck gate drive bias network.A resistor between this pin and RTN determines thevariation of off time, along with the FB pin voltage, percycle while in current limit. The off time is preset to17uS if FB =0V and decreases as the FB pin voltageincreases.

This pin is connected to the inverting input of theinternal regulation comparator. The regulationthreshold is 2.5V.

A resistor between this pin and Vin sets the switch ontime as a function of Vin. The minimum recommendedon time is 300ns at the maximum input voltage.

3

RCL

Current Limit OFF time programming pinToff = 10-5 / (0.59 + (FB / 7.22 x 10− 6 x RCL))

45

RTNFB

Circuit Ground

Feedback Signal from Regulated Output

6

RON

On time set pin

Ton = 1.42 x 10-10 RON / Vin

7Vcc

Output from the internal high voltage bias regulator.If an auxiliary voltage is available to raise the voltageVCC is nominally regulated to 7 Voltson this pin, above the regulation setpoint (7V), the

internal series pass regulator will shutdown, reducingthe IC power dissipation. Do not exceed 14V. Thisoutput provides gate drive power for the internal Buckswitch. An internal diode is provided between this pinand the BST pin. A local 0.1uF decoupling capacitoris recommended. Series pass regulator is currentlimited to 10mA.Input supply voltage

Exposed PAD, underside of the LLP packageoption

Recommended operating range: 9V to 75V.Internally bonded to the die substrate. Connect toGND potential for low thermal impedance.

8-

VinEP

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LM5007Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and specifications.VIN to GNDBST to GND

SW to GND (Steady State)ESD Rating (Note 5) Human Body Model Machine Model

80V94V-1V 2kV200V

BST to VCCBST to SWVCC to GND

All Other Inputs to GND

Lead Temperature (Soldering 4 sec)Storage Temperature Range80V14V14V

-0.3 to 7V260°C

-55°C to +150°C

Operating Ratings

VIN

Junction Temperature

(Note 1)

9V to 75V

−40°C to + 125°C

Electrical Characteristics

Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Tem-perature range. VIN = 48V, unless otherwise stated (Note 3).SymbolStartup RegulatorVCC Reg

VCC Supply

VCC undervoltage LockoutVoltage (VCC increasing)VCC Undervoltage HysteresisVCC UVLO Delay (filter)Operating Current (ICC)Shutdown/Standby CurrentBuck Switch Rds(on)

Non-Switching, FB = 3VRON = 0V

ITEST = 200mA,

VBST −VSW = 6.3V(Note 6)

TJ = 25°C

TJ = -40°C to +125°CTJ = 25°C

TJ = -40°C to +125°C

Iswitch Overdrive = 0.1A Timeto Switch OffFB=0V, RCL = 100KFB=2.3V, RCL = 100KVin = 10VRon = 200KVin = 75VRon = 200KRising

6.320635001000.74

6752001.34

VmVµsµAµAΩ

VCC Regulator OutputVCC Current Limit

(Note 4)

6.6

711

7.4

VmA

Parameter

Conditions

Min

Typ

Max

Units

Switch Characteristics

Current Limit

Gate Drive UVLO (VBST – VSW)RisingGate Drive UVLO HysteresisBreakdown VoltageVIN to GroundBreakdown VoltageBST to VCC

Current Limit ThresholdCurrent Limit Response TimeOFF time generator (test 1)OFF time generator (test 2)TON -1TON -2

Remote Shutdown ThresholdRemote Shutdown Hysteresis

3.4 80768076535 2.152900.45

4.5400

5.5

VmVVV

725225172.652.773900.740

900 3.54901.1

mAnsµsµsµsnsVmV

On Time Generator

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LM5007Symbol

Minimum Off Time Tsd θJA

Minimum Off TimerFB Reference ThresholdFB Over-Voltage ThresholdFB Bias Current

Thermal Shutdown Temp.Thermal Shutdown HysteresisJunction to Ambient

FB = 0V

Internal reference

Trip point for switch ONTrip point for switch OFF

MUA PackageSDC Package

2.445

300 2.52.8751001652520040

2.550

ns VVnA°C°C°C/W°C/W

Regulation and OV Comparators

Parameter

Conditions

Min

Typ

Max

Units

Thermal Shutdown

Thermal Resistance

Note 1:Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of thedevice is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2:For detailed information on soldering plastic MSOP and LLP packages, refer to the Packaging Data Book available from National SemiconductorCorporation.

Note 3:All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with TA = TJ = 25°C. All hot and coldlimits are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control.Note 4:The VCC output is intended as a self bias for the internal gate drive power and control circuits. Device thermal limitations limit external loading.Note 5:The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor dischargeddirectly into each pin. The machine model ESD compliance level for Pin 5 is 150V. The human body ESD compliance level for Pin 7 and 8 is 1000V.Note 6:For devices procurred in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only.

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LM5007Detailed Operating Description

The LM5007 Step Down Switching Regulator features all ofthe functions needed to implement low cost, efficient, Buckbias regulators. This high voltage regulator contains an 80V,0.7A N-Channel Buck Switch. The device is easy to apply andis provided in the MSOP-8 and the thermally enhanced LLP-8packages. The regulator is based on a hysteretic controlscheme using an on time inversely proportional to Vin. Thisfeature allows the operating frequency to remain relativelyconstant with load and input voltage variations. The hystereticcontrol requires no control loop compensation, while provid-ing very fast load transient response. An intelligent currentlimit scheme is implemented in the LM5007 with forced offtime, after current limit detection, which is inversely propor-tional to Vout. This current limiting scheme reduces loadcurrent foldback. Additional protection features include: Ther-mal Shutdown, Vcc undervoltage lockout, Gate drive under-voltage lockout and Max Duty Cycle limiter. The LM5007 canbe applied in numerous applications to efficiently regulatestep down higher voltage inputs. This regulator is well suitedfor 48 Volt Telcom and the new 42V Automotive power busranges.

In continuous conduction mode, current flows continuouslythrough the inductor and never ramps down to zero. In thismode the operating frequency is greater than the discontinu-ous mode frequency and remains relatively constant with loadand line variations. The approximate continuous mode oper-ating frequency can be calculated as follows:

The output voltage (Vout) can be programmed by two externalresistors as shown in Figure 1. The regulation point can becalculated as follows:

VOUT = 2.5 x (R1 + R2) / R2

The feedback comparator in hysteretic regulators depend up-on the output ripple voltage to switch the output transistor onand off at regular intervals. In order for the internal comparatorto respond quickly to changes in output voltage, proportionalto inductor current, a minimum amount of capacitor Equiva-lent Series Resistance (ESR) is required. A ripple voltage of25mV to 50mV is recommended at the feedback pin (FB) forstable operation. In cases where the intrinsic capacitor ESRis too small, additional series resistance may be added.

For applications where lower output voltage ripple is requiredthe load can be connected directly to the low ESR output ca-pacitor, as shown in Figure 1. The series resistor (R) willdegrade the load regulation. Another technique for enhancingthe ripple voltage at the FB pin is to place a capacitor in par-allel with the feedback divider resistor R1. The addition of thecapacitor reduces the attenuation of the ripple voltage fromthe feedback divider

Hysteretic Control Circuit Overview

The LM5007 is a Buck DC-DC regulator that uses an on timecontrol scheme. The on time is programmed by an externalresistor and varies inversely with line input voltage (Vin). Thecore regulation elements of the LM5007 are the feedbackcomparator and the on time one-shot. The regulator outputvoltage is sensed at the feedback pin (FB) and is comparedto an internal reference voltage (2.5V). If the FB signal is be-low the reference voltage, the buck switch is turned on for afixed time pulse determined by the line voltage and a pro-gramming resistor (RON). Following the on period the switchwill remain off for at least the minimum off timer period of300ns. If the FB pin voltage is still below the reference afterthe 300ns off time, the switch will turn on again for another ontime period. This switching behavior will continue until the FBpin voltage reaches the reference voltage level.

The LM5007 operates in discontinuous conduction mode atlight load currents or continuous conduction mode at heavierload currents. In discontinuous conduction mode, currentthrough the output inductor starts at zero and ramps up to apeak value during the buck switch on time and then back tozero during the off time. The inductor current remains at zerountil the next on time period starts when FB falls below theinternal reference. In discontinuous mode the operating fre-quency can be relatively low and will vary with load. Thereforeat light loads the conversion efficiency is maintained, sincethe switching losses decrease with the reduction in load cur-rent and switching frequency. The approximate discontinuousmode operating frequency can be calculated as follows:

High Voltage Bias Regulator

The LM5007 contains an internal high voltage bias regulator.The input pin (Vin) can be connected directly to line voltagesfrom 9 to 75 Volts. To avoid supply voltage transients due tolong lead inductances on the input pin (Vin Pin 8), it is alwaysrecommended to connect low ESR ceramic chip capacitor(≊ 0.1µF) between \"Vin\" pin and \"RTN\" pin (pin 4), locatedclose to LM5007. The regulator is internally current limited to10mA. Upon power up, the regulator is enabled and sourcescurrent into an external capacitor connected to the Vcc pin.When the voltage on the Vcc pin reaches the regulation pointof 7V, the controller output is enabled.

An external auxiliary supply voltage can be applied to the Vin. If the auxiliary voltage is greater than 7 Volts the internalregulator will essentially shutoff, thus reducing internal powerdissipation.

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LM500720078305

FIGURE 1. Low Ripple Output Configuration

20078306

FIGURE 2. Self Biased Configuration

Over-Voltage Comparator

The over-voltage comparator is provided to protect the outputfrom overvoltage conditions due to sudden input line voltagechanges or output loading changes. The over-voltage com-parator monitors the FB pin versus an internal 2.875V refer-ence (OV_REF). If the voltage at FB rises above OV_REF thecomparator immediately terminates the buck switch on timepulse.

ON Time generator and Shutdown

The on time of the LM5007 is set inversely proportional to theinput voltage by an external resistor connected between Ronand Vin. The Ron terminal is a low impedance input biased atapproximately 1.5V. Thus the current through the resistor andinto the Ron terminal is approximately proportional to Vin andused internally to control the on timer. This scheme of inputvoltage feed-forward hysteretic operation achieves nearlyconstant operational frequency over varying line and loadconditions. The on time equation for the LM5007 is :

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LM5007Ton = 1.42 x 10-10 x RON / VIN

The RON pin of the LM5007 also provides a shutdown functionwhich disables the regulator and significantly decreases qui-escent power dissipation. By pulling the RON pin to below 0.7V

logic threshold activates the low power shutdown mode. TheVIN quiescent current in the shutdown mode is approximately100µA internal to the LM5007 plus the current in the RON re-sistor.

20078307

FIGURE 3. Shutdown Implementation

Current Limit

The LM5007 contains an intelligent current limit off timer in-tended to reduce the foldback characteristic inherent withfixed off-time over-current protection. If the current in the Buckswitch exceeds 725mA the present cycle on time is immedi-ately terminated (cycle by cycle current limit). Following thetermination of the cycle a non-resetable current limit off timeris initiated. The duration of the off time is a function of theexternal resistor (RCI) and the FB pin voltage. When the FBpin voltage equals zero, the current limit off time is internallypreset to 17uS. This condition occurs in short circuit operationwhen a maximum amount of off time is required.

In cases of overload (not complete short circuit) the currentlimit off time can be reduced as a function of the output voltage(measured at the FB pin). Reducing the off time with smalleroverloads reduces the amount of foldback and also reducesthe initial start-up time. The current limit off time for a givenFB pin voltage and RCI resistor can be calculated by the fol-lowing equation:

Toff = 10-5 / (0.59 + (VFB / 7.22 x 10-6 x RCL))

Applications utilizing low resistance inductors and/or a lowvoltage drop rectifier may require special evaluation at highline, short circuit conditions. In this special case the preset17uS (FB = 0V) off time may be insufficient to balance theinductor volt*time product. Additional inductor resistance, out-put resistance or a larger voltage drop rectifier may be nec-essary to balance the inductor cycle volt*time product andlimit the short circuit current.

itor is charged by VCC through the internal high voltage diode.A 0.01uF ceramic capacitor connected between the BST pinand SW pin is recommended.

During each cycle when the Buck switch turns off, the SW pinis approximately 0V. When the SW pin voltage is low, thebootstrap capacitor will be charged from Vcc through the in-ternal diode. The minimum off timer, set to 300ns, ensuresthat there will be a minimum interval every cycle to rechargethe bootstrap capacitor.

An external re-circulating diode from the SW pin to ground isnecessary to carry the inductor current after the internal Buckswitch turns off. This external diode must be of the Ultra-fastor Schottky type to reduce turn-on losses and current over-shoot. The reverse voltage rating of the re-circulating diodemust be greater than the maximum line input voltage.

Thermal Protection

Internal Thermal Shutdown circuitry is provided to protect theintegrated circuit in the event the maximum junction temper-ature is exceeded. When thermal protection is activated,typically at 165 degrees Celsius, the controller is forced intoa low power reset state, disabling the output driver. This fea-ture is provided to prevent catastrophic failures from acciden-tal device overheating.

Minimum Load Current

A minimum load current of 1 mA is required to maintain properoperation. If the load current falls below that level, the boot-strap capacitor may discharge during the long off-time, andthe circuit will either shutdown, or cycle on and off at a lowfrequency. If the load current is expected to drop below 1 mAin the application, the feedback resistors should be chosenlow enough in value so they provide the minimum requiredcurrent at nominal Vout.

N - Channel Buck Switch and Driver

The LM5007 integrates an N-Channel Buck switch and as-sociated floating high voltage gate driver. This gate drivercircuit works in conjunction with an external bootstrap capac-itor and an internal high voltage diode. The bootstrap capac-www.national.com

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LM5007Operational Waveforms

LM5007 10V Output Efficiency

20078308

LM5007 Operation: VOUT = 10V, VIN = 20V, IOUT = 250mACH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current

FIGURE 4.

20078310

Operational Waveforms

FIGURE 6.

Current Limit VFB vs TOFF

RCL = 50k -600k

20078309

LM5007 Operation: VOUT = 10V, VIN = 75V, IOUT = 250mACH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current

FIGURE 5.

20078311

FIGURE 7.

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LM500720078312

FIGURE 8. VIN vs TONRON = 100k, 200k, 300k

10V, 400mA Demo Board Bill of Materials

ITEMC1C2C3C4C5D1L1R1R2R3R4R5U1

PART NUMBERC4532X7R2A105MC4532X7R1E156MC1206C104K5RACC1206C103K5RACC3216X7R2A104KT

MURA110T3SLF7045T-101MR60-1CRCW12062003FCRCW12061003FCRCW12063011FCRCW12061001FCRCW12061R00F

LM5007

DESCRIPTIONCAPACITOR, CER, TDKCAPACITOR, CER, TDKCAPACITOR, CER, KEMETCAPACITOR, CER, KEMETCAPACITOR, CER, TDKDIODE, 100V, ON SEMIBUCK INDUCTOR, TDK

RESISTORRESISTORRESISTORRESISTORRESISTOR

REGULATOR, NATIONAL

100µH200K100K3.01K1K1VALUE1µ, 100V15µ, 25V0.1µ, 50V0.01µ, 50V0.1µ, 100V

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LM5007Physical Dimensions inches (millimeters) unless otherwise noted

8-Lead MSOP PackageNS Package Number MUA08A

8-Lead LLP Package

NS Package Number SDC08A

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LM5007 High Voltage (80V) Step Down Switching RegulatorIIIIII

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