National Semiconductor LM5008 Technical data

February 5, 2008

LM5008 High Voltage (100V) Step Down Switching Regulator

General Description

The LM5008 Step Down Switching Regulator features all of the functions needed to implement a low cost, efficient, Buck bias regulator. This high voltage regulator contains an 100 V N-Channel Buck Switch. The device is easy to implement and is provided in the MSOP-8 and the thermally enhanced LLP-8 packages. The regulator is based on a hysteretic control scheme using an ON time inversely proportional to VIN. This feature allows the operating frequency to remain relatively constant. The hysteretic control requires no loop compensation. An intelligent current limit is implemented with forced OFF time, which is inversely proportional to Vout. This scheme ensures short circuit protection while providing minimum foldback. Other protection features include: Thermal Shutdown, VCC under-voltage lockout, Gate drive under-voltage lockout, and Max Duty Cycle limiter

Features

Integrated 100V, N-Channel buck switch

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Internal VCC regulator

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No loop compensation required

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Ultra-Fast transient response

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On time varies inversely with line voltage

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Operating frequency remains constant with varying line

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voltage and load current Adjustable output voltage

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Highly efficient operation

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Precision internal reference

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Low bias current

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Intelligent current limit protection

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Thermal shutdown

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Typical Applications

Non-Isolated Telecommunication Buck Regulator

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Secondary High Voltage Post Regulator

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+42V Automotive Systems

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Package

MSOP - 8

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LLP - 8 (4mm x 4mm)

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Connection Diagram

8-Lead MSOP, LLP

20097902

Ordering Information

Order Number Package Type NSC Package Drawing Supplied As

LM5008MM

LM5008MMX 3500 Units on Tape and Reel

LM5008SD

LM5008SDX 4500 Units on Tape and Reel

LM5008SDC

LM5008SDCX 4500 Units on Tape and Reel

MSOP-8 MUA08A

SDC08A

LLP-8

SDC08B

1000 Units on Tape and Reel

Typical Application Circuit and Block Diagram

LM5008

20097901

FIGURE 1.

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Pin Descriptions

Pin Name Description Application Information

1 SW Switching Node Power switching node. Connect to the output inductor,

re-circulating diode, and bootstrap capacitor.

2 BST Boost Pin (Boot–strap capacitor input) An external capacitor is required between the BST

and the SW pins. A 0.01µF ceramic capacitor is recommended. An internal diode charges the capacitor from VCC.

3 R

4 RTN Ground pin Ground for the entire circuit.

5 FB Feedback input from Regulated Output This pin is connected to the inverting input of the

6 RON/SD On time set pin

7 V

8 V

EP Exposed Pad The exposed pad has no electrical contact. Connect

Current Limit OFF time set pin

Toff = 10-5 / (0.285 + (FB / 6.35 x 10

− 6

x RCL))

A resistor between this pin and RTN sets the off-time when current limit is detected. The off-time is preset to 35µs if FB = 0V.

internal regulation comparator. The regulation threshold is 2.5V.

A resistor between this pin and VIN sets the switch on

Ton = 1.25 x 10

-10

RON / V

time as a function of VIN. The minimum recommended on time is 400ns at the maximum input voltage. This pin can be used for remote shutdown.

Output from the internal high voltage series pass regulator. Regulated at 7.0V.

If an auxiliary voltage is available to raise the voltage on this pin, above the regulation setpoint (7V), the internal series pass regulator will shutdown, reducing the IC power dissipation. Do not exceed 14V. This voltage provides gate drive power for the internal Buck switch. An internal diode is provided between this pin and the BST pin. A local 0.1µF decoupling capacitor is recommended. Series pass regulator is current limited to 10mA.

Input voltage Recommended operating range: 9.5V to 95V.

to system ground plane for reduced thermal resistance.

LM5008

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

LM5008

please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

VIN to GND -0.3V to 100V

BST to GND -0.3V to 114V SW to GND (Steady State) -1V ESD Rating (Note 5) Human Body Model 2kV BST to V

100V

BST to SW 14V VCC to GND 14V

All Other Inputs to GND -0.3 to 7V Lead Temperature (Soldering 4 sec) 200°C Storage Temperature Range -55°C to +150°C

Operating Ratings (Note 1)

Operating Junction Temperature −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 Temperature range. VIN = 48V, unless otherwise stated (Note 3).

Symbol Parameter Conditions Min Typ Max Units

VCC Supply

VCC Reg VCC Regulator Output 6.6 7 7.4 V

VCC Current Limit (Note 4) 9.5 mA

VCC undervoltage Lockout

Voltage (VCC increasing)

VCC Undervoltage Hysteresis 200

VCC UVLO Delay (filter) 100mV overdrive 10

Operating Current Non-Switching, FB = 3V 485 675 µA

Shutdown Current RON/SD = 0V 76 150 µA

Switch Characteristics

Buck Switch Rds(on) I

Gate Drive UVLO V

Gate Drive UVLO Hysteresis 430 mV

Current Limit

Current Limit Threshold 0.41 0.51 0.61 A

Current Limit Response Time I

OFF time generator (test 1) FB=0V, RCL = 100K 35 µs

OFF time generator (test 2) FB=2.3V, RCL = 100K 2.56 µs

On Time Generator

TON - 1 Vin = 10V

TON - 2 Vin = 95V

Remote Shutdown Threshold Rising 0.40 0.70 1.05 V

Remote Shutdown Hysteresis 35 mV

6.3 V

= 200mA, (Note 6) 1.15 2.47

TEST

− VSW Rising 3.4 4.5 5.5 V

BST

Overdrive = 0.1A Time

switch

400 ns

to Switch Off

2.15 2.77 3.5 µs

Ron = 200K

200 300 420 ns

Ron = 200K

9.5V to 95V

µs

Ω

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Symbol Parameter Conditions Min Typ Max Units

Minimum Off Time

Minimum Off Timer FB = 0V 300 ns

Regulation and OV Comparators

FB Reference Threshold Internal reference

2.445 2.5 2.550 V

Trip point for switch ON

FB Over-Voltage Threshold Trip point for switch OFF 2.875 V

FB Bias Current 100 nA

Thermal Shutdown

Tsd Thermal Shutdown Temp. 165 °C

Thermal Shutdown Hysteresis 25 °C

Thermal Resistance

Junction to Ambient MUA Package

200

°C/W

SDC Package 40 °C/W

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device 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 Semiconductor Corporation.

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 cold limits 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 discharged through a 1.5kΩ resistor into each pin.

Note 6: For devices procured in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only.

LM5008

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