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LM5009

LM5009 150 mA, 100V Step-Down Switching Regulator

Literature Number: SNVS402F

LM5009

November 15, 2011

150 mA, 100V Step-Down Switching Regulator

General Description

The LM5009 Step Down Switching Regulator features all of

the functions needed to implement a low cost, efficient, Buck

bias regulator. This device is capable of driving a 150 mA load

current from a 9.5V to 95V input source. The switching fre-

quency can exceed 600 kHz, depending on the input and

output voltages. The output voltage may be set from 2.5V to

85V. This high voltage regulator contains an N-Channel buck

switch and internal startup regulator. The device is easy to

implement and is provided in the MSOP-8 and the thermally

enhanced LLP-8 packages. The LM5009 is a well suited al-

ternative to a high voltage monolithic or discrete linear solu-

tion where the power loss becomes unacceptable. The

regulator’s operation is based on a control scheme using an

ON time inversely proportional to VIN. This feature allows the

operating frequency to remain relatively constant over load

and input voltage variations. The control scheme requires no

loop compensation, resulting in an ultra-fast transient re-

sponse. An intelligent current limit is implemented with forced

OFF time, which is inversely proportional to Vout. This

scheme ensures short circuit protection while providing min-

imum foldback. Other features include: Thermal Shutdown,

Vcc under-voltage lockout, Gate drive under-voltage lockout,

and Maximum Duty Cycle limiter.

Features

■Integrated N-Channel MOSFET

■Guaranteed 150 mA output current capability

■Ultra-Fast Transient Response

■No loop compensation required

■Vin feed forward provides constant operating frequency

■Switching frequency can exceed 600 kHz

■Highly efficient operation

■2% accurate 2.5V feedback from -40°C to 125°C

■Internal startup regulator

■Intelligent current limit protection

■External shutdown control

■Thermal shutdown

■MSOP-8 and thermally enhanced LLP packages

Typical Applications

■Heat sink eliminator for classic linear regulator

applications

■12V, 24V, 36V, and 48V rectified AC systems

■42V Automotive

■Non-isolated AC mains charge coupled supplies

■LED Current Source

Package

■MSOP - 8

■LLP - 8 (4mm x 4mm)

Typical Application Circuit

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Basic Stepdown Regulator

LM5009 150 mA, 100V Step-Down Switching Regulator

Connection Diagram

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8-Lead MSOP, LLP

Ordering Information

Order Number Package Type NSC Package Drawing Supplied As

LM5009MM MSOP-8 MUA08A 1000 Units on Tape and Reel

LM5009MMX MSOP-8 MUA08A 3500 Units per Reel

LM5009SDC LLP-8 SDC08B 1000 Units on Tape and Reel

LM5009SDCX LLP-8 SDC08B 4500 Units per Reel

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LM5009

Pin Descriptions

Pin Name Description Application Information

1 SW Switching output Power switching output. Connect to the inductor, re-

circulating diode, and bootstrap capacitor.

2 BST Boost Pin An external capacitor is required between the BST

and the SW pins. A 0.022 µF ceramic capacitor is

recommended. An internal diode charges the

capacitor from VCC.

3 RCL Current Limit off-time set pin 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.

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

internal regulation comparator. The regulation

threshold is 2.5V.

6 RON/SD On-time set pin A resistor between this pin and VIN sets the switch on-

time as a function of VIN. The minimum recommended

on-time is 250ns at the maximum input voltage. This

pin can be used for remote shutdown.

7 VCC Output from the internal high voltage startup

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 required.

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

EP Exposed Pad (LLP Package only) Exposed metal pad on the underside of the device. It

is recommended to connect this to the PC board

ground plane to aid in heat dissipation.

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LM5009

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the Texas Instruments Sales Office/

Distributors for availability and specifications.

VIN to RTN -0.3V to 100V

BST to RTN -0.3V to 114V

SW to RTN (Steady State) -1V

ESD Rating (Note 4)

Human Body Model 2kV

BST to VCC 100V

BST to SW 14V

VCC to RTN 14V

All Other Inputs to RTN -0.3 to 7V

For soldering specs see:

www.national.com/ms/MS/MS=SOLDERING.pdf

Storage Temperature Range -65°C to +150°C

Operating Ratings (Note 1)

VIN 9.5V to 95V

Operating Junction Temperature −40°C to + 125°C

Electrical Characteristics

Limits in standard type are for TJ = 25°C only, and limits in boldface type apply over the junction temperature (TJ) range of -40°C

to +125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent

the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated, the following

conditions apply: VIN = 48V, RON = 200kΩ. See (Note 2)

Symbol Parameter Conditions Min Typ Max Units

VCC Supply

VCC Reg VCC Regulator Output 6.6 77.4 V

VCC Current Limit (Note 3) 9.5 mA

VCC undervoltage Lockout

Voltage (VCC increasing)

6.3 V

VCC Undervoltage Hysteresis 200 mV

VCC UVLO Delay (filter) 100mV overdrive 10 µs

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

IIN Shutdown Current RON/SD = 0V 76 150 µA

Switch Characteristics

Buck Switch Rds(on) ITEST = 200mA, (Note 5) 2.0 4.4 Ω

Gate Drive UVLO VBST − VSW Rising 3.4 4.5 5.5 V

Gate Drive UVLO Hysteresis 430 mV

Current Limit

Current Limit Threshold 0.25 0.31 0.37 A

Current Limit Response Time Iswitch Overdrive = 0.1A Time

to Switch Off

400 ns

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

Ron = 200K

2.15 2.77 3.5 µs

TON - 2 Vin = 95V

Ron = 200K

200 300 420 ns

Remote Shutdown Threshold Rising 0.40 0.70 1.05 V

Remote Shutdown Hysteresis 35 mV

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LM5009

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

Trip point for switch ON

2.445 2.5 2.550 V

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

FB Bias Current 1 nA

Thermal Shutdown

Tsd Thermal Shutdown Temp. 165 °C

Thermal Shutdown Hysteresis 25 °C

Thermal Resistance

θJA 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: 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 3: 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 4: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.

Note 5: For devices procured in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only.

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LM5009

Typical Performance Characteristics

On-Time vs VIN and RON

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VCC vs VIN and FS

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Current Limit Off-Time vs VFB and RCL

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VCC vs ICC and VIN

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ICC Current vs Applied VCC Voltage

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LM5009

Typical Application Circuit and Block Diagram

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FIGURE 1.

Functional Description

The LM5009 Step Down Switching Regulator features all the

functions needed to implement a low cost, efficient, Buck bias

power converter. This high voltage regulator contains a 100

V N-Channel Buck Switch, is easy to implement and is pro-

vided in the MSOP-8 and the thermally enhanced LLP-8

packages. The regulator is based on a control scheme using

an on-time inversely proportional to VIN. The control scheme

requires no loop compensation. Current limit is implemented

with forced off-time, which is inversely proportional to VOUT.

This scheme ensures short circuit protection while providing

minimum foldback. The Functional Block Diagram of the

LM5009 is shown in Figure 1.

The LM5009 can be applied in numerous applications to ef-

ficiently regulate down higher voltages. This regulator is well

suited for 48 Volt Telecom and the 42V Automotive power bus

ranges. Additional features include: Thermal Shutdown, VCC

under-voltage lockout, Gate drive under-voltage lockout, Max

Duty Cycle limit timer and the intelligent current limit off timer.

Control Circuit Overview

The LM5009 is a Buck DC-DC regulator that uses a control

scheme in which the on-time varies inversely with line voltage

(VIN). Control is based on a comparator and the on-time one-

shot, with the output voltage feedback (FB) compared to an

internal reference (2.5V). If the FB level is below the reference

the buck switch is turned on for a fixed time determined by the

line voltage and a programming resistor (RON). Following the

ON period the switch will remain off for at least the minimum

off-timer period of 300 ns. If FB is still below the reference at

that time the switch will turn on again for another on-time pe-

riod. This will continue until regulation is achieved, at which

time the off-time increases based on the required duty cycle.

The LM5009 operates in discontinuous conduction mode at

light load currents, and continuous conduction mode at heavy

load current. In discontinuous conduction mode, current

through the output inductor starts at zero and ramps up to a

peak during the on-time, then ramps back to zero before the

end of the off-time. The next on-time period starts when the

voltage at FB falls below the internal reference - until then the

inductor current remains zero. In this mode the operating fre-

quency is lower than in continuous conduction mode, and

varies with load current. Therefore at light loads the conver-

sion efficiency is maintained, since the switching losses re-

duce with the reduction in load and frequency. The discon-

tinuous operating frequency can be calculated as follows:

where RL = the load resistance

In continuous conduction mode, current flows continuously

through the inductor and never ramps down to zero. In this

mode the operating frequency is greater than the discontinu-

ous mode frequency and remains relatively constant with load

and line variations. The approximate continuous mode oper-

ating frequency can be calculated as follows:

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LM5009

(1)

The output voltage (VOUT) is programmed by two external re-

sistors as shown in Figure 1. The regulation point is calculated

as follows:

VOUT = 2.5 x (R1 + R2) / R2

This regulator regulates the output voltage based on ripple

voltage at the feedback input, requiring a minimum amount of

ESR for the output capacitor C2. A minimum of 25mV of ripple

voltage at the feedback pin (FB) is required for the LM5009.

In cases where the capacitor ESR is too small, additional se-

ries resistance may be required (R3 in Figure 1).

For applications where lower output voltage ripple is required

the output can be taken directly from a low ESR output ca-

pacitor, as shown in Figure 2. However, R3 slightly degrades

the load regulation.

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FIGURE 2. Low Ripple Output Configuration

High Voltage Start-Up Regulator

The LM5009 contains an internal high voltage startup regu-

lator. The input pin (VIN) can be connected directly to line

voltages up to 95 Volts, with transient capability to 100 volts.

The regulator is internally current limited at 9.5mA. Upon

power up, the regulator sources current into the external ca-

pacitor at VCC (C3). When the voltage on the VCC pin reach-

es the under-voltage lockout threshold of 6.3V, the buck

switch is enabled.

In applications involving a high value for VIN, where power

dissipation in the VCC regulator is a concern, an auxiliary volt-

age can be diode connected to the VCC pin. Setting the

voltage between 8V and 14V shuts off the internal regulator,

reducing internal power dissipation. See Figure 3. The current

required into the VCC pin is shown in the Typical Performance

Characteristics.

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FIGURE 3. Self Biased Configuration

Regulation Comparator

The feedback voltage at FB is compared to an internal 2.5V

reference. In normal operation (the output voltage is regulat-

ed), an on-time period is initiated when the voltage at FB falls

below 2.5V. The buck switch will stay on for the programmed

on-time, causing the FB voltage to rise above 2.5V. After the

on-time period, the buck switch will stay off until the FB volt-

age again falls below 2.5V. During start-up, the FB voltage

will be below 2.5V at the end of each on-time, resulting in the

minimum off-time. Bias current at the FB pin is less than 5 nA

over temperature.

Over-Voltage Comparator

The feedback voltage at FB is compared to an internal 2.875V

reference. If the voltage at FB rises above 2.875V the on-time

pulse is immediately terminated. This condition can occur if

the input voltage, or the output load, change suddenly. The

buck switch will not turn on again until the voltage at FB falls

below 2.5V.

ON-Time Generator and Shutdown

The on-time for the LM5009 is determined by the RON resistor,

and is inversely proportional to the input voltage (Vin), result-

ing in a nearly constant frequency as Vin is varied over its

range. The on-time equation is:

TON = 1.25 x 10-10 x RON / VIN (2)

RON should be selected for a minimum on-time (at maximum

VIN) greater than 250 ns, for proper current limit operation.

This requirement limits the maximum frequency for each ap-

plication, depending on VIN and VOUT.

The LM5009 can be remotely disabled by taking the RON/SD

pin to ground. See Figure 4. The voltage at the RON/SD pin

is between 1.7V and 5V, depending on Vin and the value of

the RON resistor.

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LM5009

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FIGURE 4. Shutdown Implementation

Current Limit

The LM5009 contains an intelligent current limit OFF timer. If

the current in the Buck switch exceeds 0.31A the present cy-

cle is immediately terminated, and a non-resetable OFF timer

is initiated. The length of off-time is controlled by an external

resistor (RCL) and the FB voltage. When FB = 0V, a maximum

off-time is required, and the time is preset to 35µs. This con-

dition occurs when the output is shorted, and during the initial

part of start-up. This amount of time ensures safe short circuit

operation up to the maximum input voltage of 95V. In cases

of overload where the FB voltage is above zero volts (not a

short circuit) the current limit off-time will be less than 35µs.

Reducing the off-time during less severe overloads reduces

the amount of foldback, recovery time, and the start-up time.

The off-time is calculated from the following equation:

(3)

The current limit sensing circuit is blanked for the first 50-70ns

of each on-time so it is not falsely tripped by the current surge

which occurs at turn-on. The current surge is required by the

re-circulating diode (D1) for its turn-off recovery.

N - Channel Buck Switch and Driver

The LM5009 integrates an N-Channel buck switch and asso-

ciated floating high voltage gate driver. The gate driver circuit

works in conjunction with an external bootstrap capacitor and

an internal high voltage diode. A 0.022 µF ceramic capacitor

(C4) connected between the BST pin and SW pin provides

the voltage to the driver during the on-time.

During each off-time, the SW pin is at approximately -1V, and

the bootstrap capacitor charges from Vcc through the internal

diode. The minimum OFF timer ensures a minimum time each

cycle to recharge the bootstrap capacitor.

An external re-circulating diode (D1) carries the inductor cur-

rent after the internal buck switch turns off. This diode should

be of the Ultra-fast or Schottky type to minimize turn-on losses

and current over-shoot.

Thermal Protection

The LM5009 should be operated so the junction temperature

does not exceed 125°C during normal operation. An internal

Thermal Shutdown circuit is provided to protect the LM5009

in the event of a higher than normal junction temperature.

When activated, typically at 165°C, the controller is forced into

a low power reset state, disabling the buck switch. This fea-

ture prevents catastrophic failures from accidental device

overheating. When the junction temperature reduces below

140°C (typical hysteresis = 25°C), the buck switch is enabled,

and normal operation is resumed.

Applications Information

SELECTION OF EXTERNAL COMPONENTS

A guide for determining the component values will be illus-

trated with a design example. Refer to Figure 1. The following

steps will configure the LM5009 for:

•Input voltage range (Vin): 12V to 90V

•Output voltage (VOUT1): 10V

•Load current (for continuous conduction mode): 100mA to

150mA

R1 and R2: From Figure 1, VOUT1 = VFB x (R1 + R2) / R2, and

since VFB = 2.5V, the ratio of R1 to R2 calculates as 3:1.

Standard values of 3.01 kΩ (R1) and 1.00 kΩ (R2) are cho-

sen. Other values could be used as long as the 3:1 ratio is

maintained. The selected values, however, provide a small

amount of output loading (2.5 mA) in the event the main load

is disconnected. This allows the circuit to maintain regulation

until the main load is reconnected.

Fs and RON: Unless the application requires a specific fre-

quency, the choice of frequency is generally a compromise

since it affects the size of L1 and C2, and the switching losses.

The maximum allowed frequency, based on a minimum on-

time of 250 ns, is calculated from:

FMAX = VOUT / (VINMAX x 250 ns)

For this exercise, Fmax = 444 kHz. From equation 1, RON

calculates to 180 kΩ. A standard value 237 kΩ resistor will be

used to allow for tolerances in equation 1, resulting in a nom-

inal frequency of 337 kHz.

L1: The main parameter affected by the inductor is the output

current ripple amplitude. The choice of inductor value there-

fore depends on both the minimum and maximum load cur-

rents, keeping in mind that the maximum ripple current occurs

at maximum Vin.

a) Minimum load current: To maintain continuous conduc-

tion at minimum Io (100 mA), the ripple amplitude (IOR) must

be less than 200 mA p-p so the lower peak of the waveform

does not reach zero. L1 is calculated using the following

equation:

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LM5009

At Vin = 90V, L1(min) calculates to 132 µH. The next larger

standard value (150 µH) is chosen and with this value IOR

calculates to 176 mA p-p at Vin = 90V, and 33 mA p-p at Vin

= 12V.

b) Maximum load current: At a load current of 150 mA, the

peak of the ripple waveform must not reach the minimum

guaranteed value of the LM5009’s current limit threshold (250

mA). Therefore the ripple amplitude must be less than 200

mA p-p, which is already satisfied in the above calculation.

With L1 = 150 µH, at maximum Vin and Io, the peak of the

ripple will be 238 mA. While L1 must carry this peak current

without saturating or exceeding its temperature rating, it also

must be capable of carrying the maximum guaranteed value

of the LM5009’s current limit threshold (370 mA) without sat-

urating, since the current limit is reached during startup.

C3: The capacitor on the VCC output provides not only noise

filtering and stability, but also prevents false triggering of the

VCC UVLO at the buck switch on/off transitions. For this rea-

son, C3 should be no smaller than 0.1 µF.

C2, and R3: When selecting the output filter capacitor C2, the

items to consider are ripple voltage due to its ESR, ripple

voltage due to its capacitance, and the nature of the load.

a) ESR and R3: A low ESR for C2 is generally desirable so

as to minimize power losses and heating within the capacitor.

However, this regulator requires a minimum amount of ripple

voltage at the feedback input for proper loop operation. For

the LM5009 the minimum ripple required at pin 5 is 25 mV p-

p, requiring a minimum ripple at VOUT1 of 100 mV. Since the

minimum ripple current (at minimum Vin) is 33 mA p-p, the

minimum ESR required at VOUT1 is 3 Ω. Since quality capac-

itors for SMPS applications have an ESR considerably less

than this, R3 is inserted as shown in Figure 1. R3’s value,

along with C2’s ESR, must result in at least 25 mV p-p ripple

at pin 5. Generally, R3 will be 0.5 Ω to 5.0 Ω.

b) Nature of the Load: The load can be connected to

VOUT1 or VOUT2. VOUT1 provides good regulation, but with a

ripple voltage which ranges from 100 mV (@ Vin = 12V) to

580 mV (@Vin = 90V). Alternatively, VOUT2 provides low ripple

(3 mV to 13 mV) but lower regulation due to R3.

C2 should generally be no smaller than 3.3 µF. Typically, its

value is 10 µF to 20 µF, with the optimum value determined

by the load. If the load current is fairly constant, a small value

suffices for C2. If the load current includes significant tran-

sients, a larger value is necessary. For each application,

experimentation is needed to determine the optimum values

for R3 and C2.

C) Ripple Reduction: The ripple amplitude at VOUT1 can be

reduced by reducing R3, and adding a capacitor across R1

so as to tranfer the ripple at VOUT1 directly to the FB pin, with-

out attenuation. The new value of R3 is calculated from:

R3 = 25 mV/IOR(min)

where IOR(min) is the minimum ripple current amplitude - 33

mAp-p in this example. The added capacitor's value is calcu-

lated from:

C = TON(max)/(R1 // R2)

where TON(max) is the maximum on-time (at minimum Vin). The

selected capacitor should be larger than the value calculated

above.

RCL: When a current limit condition is detected, the minimum

off-time set by this resistor must be greater than the maximum

normal off-time which occurs at maximum Vin. Using equation

2, the minimum on-time is 0.329 µs, yielding a maximum off-

time of 2.63 µs. This is increased by 82 ns (to 2.72 µs) due to

a ±25% tolerance of the on-time. This value is then increased

to allow for:

The response time of the current limit detection loop

(400ns),

The off-time determined by equation 3 has a ±25% toler-

ance,

tOFFCL(MIN) = (2.72 µs x 1.25) + 0.4 µs= 3.8 µs

Using equation 3, RCL calculates to 167 kΩ (at VFB = 2.5V).

The closest standard value is 169 kΩ.

D1: The important parameters are reverse recovery time and

forward voltage. The reverse recovery time determines how

long the reverse current surge lasts each time the buck switch

is turned on. The forward voltage drop is significant in the

event the output is short-circuited as it is only this diode’s

voltage which forces the inductor current to reduce during the

forced off-time. For this reason, a higher voltage is better, al-

though that affects efficiency. A good choice is an ultrafast

power or Schottky diode with a reverse recovery time of ≊30

ns, and a forward voltage drop of ≊0.7V. Other types of diodes

may have a lower forward voltage drop, but may have longer

recovery times, or greater reverse leakage. D1’s reverse volt-

age rating must be at least as great as the maximum Vin, and

its current rating be greater than the maximum current limit

threshold (370 mA).

C1: This capacitor’s purpose is to supply most of the switch

current during the on-time, and limit the voltage ripple at VIN,

on the assumption that the voltage source feeding VIN has

an output impedance greater than zero. At maximum load

current, when the buck switch turns on, the current into pin 8

will suddenly increase to the lower peak of the output current

waveform, ramp up to the peak value, then drop to zero at

turn-off. The average input current during this on-time is the

load current (150 mA). For a worst case calculation, C1 must

supply this average load current during the maximum on-time.

To keep the input voltage ripple to less than 2V (for this ex-

ercise), C1 calculates to:

Quality ceramic capacitors in this value have a low ESR which

adds only a few millivolts to the ripple. It is the capacitance

which is dominant in this case. To allow for the capacitor’s

tolerance, temperature effects, and voltage effects, a 1.0 µF,

100V, X7R capacitor will be used.

C4: The recommended value is 0.022 µF for C4, as this is

appropriate in the majority of applications. A high quality ce-

ramic capacitor, with low ESR is recommended as C4 sup-

plies the surge current to charge the buck switch gate at turn-

on. A low ESR also ensures a quick recharge during each off-

time. At minimum VIN, when the on-time is at maximum, it is

possible during start-up that C4 will not fully recharge during

each 300 ns off-time. The circuit will not be able to complete

the start-up, and achieve output regulation. This can occur

when the frequency is intended to be low (e.g., RON = 500K).

In this case C4 should be increased so it can maintain suffi-

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LM5009

cient voltage across the buck switch driver during each on-

time.

C5: This capacitor helps avoid supply voltage transients and

ringing due to long lead inductance at VIN. A low ESR, 0.1µF

ceramic chip capacitor is recommended, located close to the

LM5009.

FINAL CIRCUIT

The final circuit is shown in Figure 5. The circuit was tested,

and the resulting performance is shown in Figure 6 through

Figure 9. For these graphs, the load current was varied from

50mA to 200mA.

MINIMUM LOAD CURRENT

A minimum load current of 1 mA is required to maintain proper

operation. If the load current falls below that level, the boot-

strap capacitor may discharge during the long off-time, and

the circuit will either shutdown, or cycle on and off at a low

frequency. If the load current is expected to drop below 1 mA

in the application, the feedback resistors should be chosen

low enough in value so they provide the minimum required

current at nominal Vout.

PC BOARD LAYOUT

The LM5009 regulation and over-voltage comparators are

very fast, and as such will respond to short duration noise

pulses. Layout considerations are therefore critical for opti-

mum performance. The components at pins 1, 2, 3, 5, and 6

should be as physically close as possible to the IC, thereby

minimizing noise pickup in the PC tracks. The current loop

formed by D1, L1, and C2 should be as small as possible. The

ground connection from C2 to C1 should be as short and di-

rect as possible.

If the internal dissipation of the LM5009 produces excessive

junction temperatures during normal operation, good use of

the pc board’s ground plane can help considerably to dissi-

pate heat. The exposed pad on the bottom of the LLP-8

package can be soldered to a ground plane on the PC board,

and that plane should extend out from beneath the IC to help

dissipate the heat. Additionally, the use of wide PC board

traces, where possible, can also help conduct heat away from

the IC. Judicious positioning of the PC board within the end

product, along with use of any available air flow (forced or

natural convection) can help reduce the junction tempera-

tures.

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FIGURE 5. LM5009 Example Circuit

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LM5009

Bill of Materials (Circuit of Figure 5)

Item Description Part Number Value

C1 Ceramic Capacitor TDK C4532X7R2A105M 1 µF, 100V

C2 Ceramic Capacitor TDK C4532X7R1E156M 15 µF, 25V

C3 Ceramic Capacitor Kemet C1206C104K5RAC 0.1 µF, 50V

C4 Ceramic Capacitor Kemet C1206C223K5RAC 0.022 µF, 50V

C5 Ceramic Capacitor TDK C3216X7R2A104M 0.1 µF, 100V

D1 Schottky Power Diode Diodes Inc. DFLS1100 100V, 1A

L1 Power Inductor TDK SLF7045T-151MR33 150 µH

R1 Resistor Vishay CRCW12063011F 3.01 kΩ

R2 Resistor Vishay CRCW12061001F 1.0 kΩ

R3 Resistor Vishay CRCW12063R00F 3.0 Ω

RON Resistor Vishay CRCW12062373F 237 kΩ

RCL Resistor Vishay CRCW12061693F 169 kΩ

U1 Switching Regulator National Semiconductor LM5009

20165823

FIGURE 6. Efficiency vs Load Current and VIN

20165827

FIGURE 7. Efficiency vs VIN and Load Current

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LM5009

20165824

FIGURE 8. VOUT vs Load Current

20165831

FIGURE 9. Current Limit vs VIN

13 www.ti.com

LM5009

Physical Dimensions inches (millimeters) unless otherwise noted

8-Lead MSOP Package

NS Package Number MUA08A

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LM5009

8-Lead LLP Package

NS Package Number SDC08B

15 www.ti.com

LM5009

Notes

LM5009 150 mA, 100V Step-Down Switching Regulator

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