LM2736YMK/NOPB - NATIONAL SEMICONDUCTOR

LM2736

LM2736 Thin SOT23 750mA Load Step-Down DC-DC Regulator

Literature Number: SNVS316E

LM2736

September 19, 2011

Thin SOT23 750mA Load Step-Down DC-DC Regulator

General Description

The LM2736 regulator is a monolithic, high frequency, PWM

step-down DC/DC converter in a 6-pin Thin SOT23 package.

It provides all the active functions to provide local DC/DC

conversion with fast transient response and accurate regula-

tion in the smallest possible PCB area.

With a minimum of external components and online design

support through WEBENCH®™, the LM2736 is easy to use.

The ability to drive 750mA loads with an internal 350mΩ

NMOS switch using state-of-the-art 0.5µm BiCMOS technol-

ogy results in the best power density available. The world

class control circuitry allows for on-times as low as 13ns, thus

supporting exceptionally high frequency conversion over the

entire 3V to 18V input operating range down to the minimum

output voltage of 1.25V. Switching frequency is internally set

to 550kHz (LM2736Y) or 1.6MHz (LM2736X), allowing the

use of extremely small surface mount inductors and chip ca-

pacitors. Even though the operating frequencies are very

high, efficiencies up to 90% are easy to achieve. External

shutdown is included, featuring an ultra-low stand-by current

of 30nA. The LM2736 utilizes current-mode control and inter-

nal compensation to provide high-performance regulation

over a wide range of operating conditions. Additional features

include internal soft-start circuitry to reduce inrush current,

pulse-by-pulse current limit, thermal shutdown, and output

over-voltage protection.

Features

■Thin SOT23-6 package

■3.0V to 18V input voltage range

■1.25V to 16V output voltage range

■750mA output current

■550kHz (LM2736Y) and 1.6MHz (LM2736X)

switching frequencies

■350mΩ NMOS switch

■30nA shutdown current

■1.25V, 2% internal voltage reference

■Internal soft-start

■Current-Mode, PWM operation

■WEBENCH® online design tool

■Thermal shutdown

Applications

■Local Point of Load Regulation

■Core Power in HDDs

■Set-Top Boxes

■Battery Powered Devices

■USB Powered Devices

■DSL Modems

■Notebook Computers

Typical Application Circuit

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Efficiency vs Load Current "X"

VIN = 5V, VOUT = 3.3V

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WEBENCH™ is a trademark of Transim.

LM2736 Thin SOT23 750mA Load Step-Down DC-DC Regulator

Connection Diagrams

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6-Lead TSOT

NS Package Number MK06A

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Pin 1 Indentification

Ordering Information

Order Number Package Type NSC Package Drawing Package Marking Supplied As

LM2736XMK

TSOT-6 MK06A

SHAB 1000 Units on Tape and Reel

LM2736YMK SHBB 1000 Units on Tape and Reel

LM2736XMKX SHAB 3000 Units on Tape and Reel

LM2736YMKX SHBB 3000 Units on Tape and Reel

* Contact the local sales office for the lead-free package.

Pin Descriptions

Pin Name Function

1 BOOST Boost voltage that drives the internal NMOS control switch. A

bootstrap capacitor is connected between the BOOST and SW pins.

2 GND Signal and Power ground pin. Place the bottom resistor of the

feedback network as close as possible to this pin for accurate

regulation.

3 FB Feedback pin. Connect FB to the external resistor divider to set output

voltage.

4 EN Enable control input. Logic high enables operation. Do not allow this

pin to float or be greater than VIN + 0.3V.

5 VIN Input supply voltage. Connect a bypass capacitor to this pin.

6 SW Output switch. Connects to the inductor, catch diode, and bootstrap

capacitor.

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LM2736

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VIN -0.5V to 22V

SW Voltage -0.5V to 22V

Boost Voltage -0.5V to 28V

Boost to SW Voltage -0.5V to 6.0V

FB Voltage -0.5V to 3.0V

EN Voltage -0.5V to (VIN + 0.3V)

Junction Temperature 150°C

ESD Susceptibility (Note 2) 2kV

Storage Temp. Range -65°C to 150°C

Soldering Information

Infrared/Convection Reflow (15sec) 220°C

Wave Soldering Lead Temp. (10sec) 260°C

Operating Ratings (Note 1)

VIN 3V to 18V

SW Voltage -0.5V to 18V

Boost Voltage -0.5V to 23V

Boost to SW Voltage 1.6V to 5.5V

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

Thermal Resistance θJA (Note 3)118°C/W

Electrical Characteristics

Specifications with standard typeface are for TJ = 25°C, and those in boldface type apply over the full Operating Temperature

Range (TJ = -40°C to 125°C). VIN = 5V, VBOOST - VSW = 5V unless otherwise specified. Datasheet min/max specification limits are

guaranteed by design, test, or statistical analysis.

Symbol Parameter Conditions Min

(Note 4)

Typ

(Note 5)

Max

(Note 4)Units

VFB Feedback Voltage 1.225 1.250 1.275 V

ΔVFB/ΔVIN Feedback Voltage Line Regulation VIN = 3V to 18V 0.01 % / V

IFB Feedback Input Bias Current Sink/Source 10 250 nA

UVLO

Undervoltage Lockout VIN Rising 2.74 2.90

Undervoltage Lockout VIN Falling 2.0 2.3

UVLO Hysteresis 0.30 0.44 0.62

FSW Switching Frequency LM2736X 1.2 1.6 1.9 MHz

LM2736Y 0.40 0.55 0.66

DMAX Maximum Duty Cycle LM2736X 85 92 %

LM2736Y 90 96

DMIN Minimum Duty Cycle LM2736X 2 %

LM2736Y 1

RDS(ON) Switch ON Resistance VBOOST - VSW = 3V 350 650 mΩ

ICL Switch Current Limit VBOOST - VSW = 3V 1.0 1.5 2.3 A

IQQuiescent Current Switching 1.5 2.5 mA

Quiescent Current (shutdown) VEN = 0V 30 nA

IBOOST Boost Pin Current LM2736X (50% Duty Cycle) 2.2 3.3 mA

LM2736Y (50% Duty Cycle) 0.9 1.6

VEN_TH

Shutdown Threshold Voltage VEN Falling 0.4 V

Enable Threshold Voltage VEN Rising 1.8

IEN Enable Pin Current Sink/Source 10 nA

ISW Switch Leakage 40 nA

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see Electrical Characteristics.

Note 2: Human body model, 1.5kΩ in series with 100pF.

Note 3: Thermal shutdown will occur if the junction temperature exceeds 165°C. The maximum power dissipation is a function of TJ(MAX) , θJA and TA . The

maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) – TA)/θJA . All numbers apply for packages soldered directly onto a 3” x 3” PC

board with 2oz. copper on 4 layers in still air. For a 2 layer board using 1 oz. copper in still air, θJA = 204°C/W.

Note 4: Guaranteed to National’s Average Outgoing Quality Level (AOQL).

Note 5: Typicals represent the most likely parametric norm.

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LM2736

Typical Performance Characteristics All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH ("X"),

L1 = 10 µH ("Y"), and TA = 25°C, unless specified otherwise.

Efficiency vs Load Current - "X" VOUT = 5V

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Efficiency vs Load Current - "Y" VOUT = 5V

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Efficiency vs Load Current - "X" VOUT = 3.3V

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Efficiency vs Load Current - "Y" VOUT = 3.3V

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Efficiency vs Load Current - "X" VOUT = 1.5V

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Efficiency vs Load Current - "Y" VOUT = 1.5V

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LM2736

Oscillator Frequency vs Temperature - "X"

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Oscillator Frequency vs Temperature - "Y"

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Current Limit vs Temperature

VIN = 18V, VIN = 5V

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VFB vs Temperature

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RDSON vs Temperature

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IQ Switching vs Temperature

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LM2736

Line Regulation - "X"

VOUT = 1.5V, IOUT = 500mA

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Line Regulation - "Y"

VOUT = 1.5V, IOUT = 500mA

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Line Regulation - "X"

VOUT = 3.3V, IOUT = 500mA

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Line Regulation - "Y"

VOUT = 3.3V, IOUT = 500mA

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LM2736

Block Diagram

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FIGURE 1.

Application Information

THEORY OF OPERATION

The LM2736 is a constant frequency PWM buck regulator IC

that delivers a 750mA load current. The regulator has a preset

switching frequency of either 550kHz (LM2736Y) or 1.6MHz

(LM2736X). These high frequencies allow the LM2736 to op-

erate with small surface mount capacitors and inductors,

resulting in DC/DC converters that require a minimum amount

of board space. The LM2736 is internally compensated, so it

is simple to use, and requires few external components. The

LM2736 uses current-mode control to regulate the output

voltage.

The following operating description of the LM2736 will refer

to the Simplified Block Diagram (Figure 1) and to the wave-

forms in Figure 2. The LM2736 supplies a regulated output

voltage by switching the internal NMOS control switch at con-

stant frequency and variable duty cycle. A switching cycle

begins at the falling edge of the reset pulse generated by the

internal oscillator. When this pulse goes low, the output con-

trol logic turns on the internal NMOS control switch. During

this on-time, the SW pin voltage (VSW) swings up to approxi-

mately VIN, and the inductor current (IL) increases with a linear

slope. IL is measured by the current-sense amplifier, which

generates an output proportional to the switch current. The

sense signal is summed with the regulator’s corrective ramp

and compared to the error amplifier’s output, which is propor-

tional to the difference between the feedback voltage and

VREF. When the PWM comparator output goes high, the out-

put switch turns off until the next switching cycle begins.

During the switch off-time, inductor current discharges

through Schottky diode D1, which forces the SW pin to swing

below ground by the forward voltage (VD) of the catch diode.

The regulator loop adjusts the duty cycle (D) to maintain a

constant output voltage.

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FIGURE 2. LM2736 Waveforms of SW Pin Voltage and

Inductor Current

BOOST FUNCTION

Capacitor CBOOST and diode D2 in Figure 3 are used to gen-

erate a voltage VBOOST. VBOOST - VSW is the gate drive voltage

to the internal NMOS control switch. To properly drive the in-

ternal NMOS switch during its on-time, VBOOST needs to be at

least 1.6V greater than VSW. Although the LM2736 will oper-

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LM2736

ate with this minimum voltage, it may not have sufficient gate

drive to supply large values of output current. Therefore, it is

recommended that VBOOST be greater than 2.5V above VSW

for best efficiency. VBOOST – VSW should not exceed the max-

imum operating limit of 5.5V.

5.5V > VBOOST – VSW > 2.5V for best performance.

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FIGURE 3. VOUT Charges CBOOST

When the LM2736 starts up, internal circuitry from the

BOOST pin supplies a maximum of 20mA to CBOOST. This

current charges CBOOST to a voltage sufficient to turn the

switch on. The BOOST pin will continue to source current to

CBOOST until the voltage at the feedback pin is greater than

1.18V.

There are various methods to derive VBOOST:

1. From the input voltage (VIN)

2. From the output voltage (VOUT)

3. From an external distributed voltage rail (VEXT)

4. From a shunt or series zener diode

In the Simplifed Block Diagram of Figure 1, capacitor

CBOOST and diode D2 supply the gate-drive current for the

NMOS switch. Capacitor CBOOST is charged via diode D2 by

VIN. During a normal switching cycle, when the internal NMOS

control switch is off (TOFF) (refer to Figure 2), VBOOST equals

VIN minus the forward voltage of D2 (VFD2), during which the

current in the inductor (L) forward biases the Schottky diode

D1 (VFD1). Therefore the voltage stored across CBOOST is

VBOOST - VSW = VIN - VFD2 + VFD1

When the NMOS switch turns on (TON), the switch pin rises

VSW = VIN – (RDSON x IL),

forcing VBOOST to rise thus reverse biasing D2. The voltage at

VBOOST is then

VBOOST = 2VIN – (RDSON x IL) – VFD2 + VFD1

which is approximately

2VIN - 0.4V

for many applications. Thus the gate-drive voltage of the

NMOS switch is approximately

VIN - 0.2V

An alternate method for charging CBOOST is to connect D2 to

the output as shown in Figure 3. The output voltage should

be between 2.5V and 5.5V, so that proper gate voltage will be

applied to the internal switch. In this circuit, CBOOST provides

a gate drive voltage that is slightly less than VOUT.

In applications where both VIN and VOUT are greater than

5.5V, or less than 3V, CBOOST cannot be charged directly from

these voltages. If VIN and VOUT are greater than 5.5V,

CBOOST can be charged from VIN or VOUT minus a zener volt-

age by placing a zener diode D3 in series with D2, as shown

in Figure 4. When using a series zener diode from the input,

ensure that the regulation of the input supply doesn’t create

a voltage that falls outside the recommended VBOOST voltage.

(VINMAX – VD3) < 5.5V

(VINMIN – VD3) > 1.6V

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FIGURE 4. Zener Reduces Boost Voltage from VIN

An alternative method is to place the zener diode D3 in a

shunt configuration as shown in Figure 5. A small 350mW to

500mW 5.1V zener in a SOT-23 or SOD package can be used

for this purpose. A small ceramic capacitor such as a 6.3V,

0.1µF capacitor (C4) should be placed in parallel with the

zener diode. When the internal NMOS switch turns on, a pulse

of current is drawn to charge the internal NMOS gate capac-

itance. The 0.1 µF parallel shunt capacitor ensures that the

VBOOST voltage is maintained during this time.

Resistor R3 should be chosen to provide enough RMS current

to the zener diode (D3) and to the BOOST pin. A recom-

mended choice for the zener current (IZENER) is 1 mA. The

current IBOOST into the BOOST pin supplies the gate current

of the NMOS control switch and varies typically according to

the following formula for the X - version:

IBOOST = 0.49 x (D + 0.54) x (VZENER – VD2) mA

IBOOST can be calculated for the Y version using the following:

IBOOST = 0.20 x (D + 0.54) x (VZENER - VD2) µA

where D is the duty cycle, VZENER and VD2 are in volts, and

IBOOST is in milliamps. VZENER is the voltage applied to the

anode of the boost diode (D2), and VD2 is the average forward

voltage across D2. Note that this formula for IBOOST gives typ-

ical current. For the worst case IBOOST, increase the current

by 40%. In that case, the worst case boost current will be

IBOOST-MAX = 1.4 x IBOOST

R3 will then be given by

R3 = (VIN - VZENER) / (1.4 x IBOOST + IZENER)

For example, using the X-version let VIN = 10V, VZENER = 5V,

VD2 = 0.7V, IZENER = 1mA, and duty cycle D = 50%. Then

IBOOST = 0.49 x (0.5 + 0.54) x (5 - 0.7) mA = 2.19mA

R3 = (10V - 5V) / (1.4 x 2.19mA + 1mA) = 1.23kΩ

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LM2736

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FIGURE 5. Boost Voltage Supplied from the Shunt Zener

on VIN

ENABLE PIN / SHUTDOWN MODE

The LM2736 has a shutdown mode that is controlled by the

enable pin (EN). When a logic low voltage is applied to EN,

the part is in shutdown mode and its quiescent current drops

to typically 30nA. Switch leakage adds another 40nA from the

input supply. The voltage at this pin should never exceed

VIN + 0.3V.

SOFT-START

This function forces VOUT to increase at a controlled rate dur-

ing start up. During soft-start, the error amplifier’s reference

voltage ramps from 0V to its nominal value of 1.25V in ap-

proximately 200µs. This forces the regulator output to ramp

up in a more linear and controlled fashion, which helps reduce

inrush current.

OUTPUT OVERVOLTAGE PROTECTION

The overvoltage comparator compares the FB pin voltage to

a voltage that is 10% higher than the internal reference Vref.

Once the FB pin voltage goes 10% above the internal refer-

ence, the internal NMOS control switch is turned off, which

allows the output voltage to decrease toward regulation.

UNDERVOLTAGE LOCKOUT

Undervoltage lockout (UVLO) prevents the LM2736 from op-

erating until the input voltage exceeds 2.74V(typ).

The UVLO threshold has approximately 440mV of hysteresis,

so the part will operate until VIN drops below 2.3V(typ). Hys-

teresis prevents the part from turning off during power up if

VIN is non-monotonic.

CURRENT LIMIT

The LM2736 uses cycle-by-cycle current limiting to protect

the output switch. During each switching cycle, a current limit

comparator detects if the output switch current exceeds 1.5A

(typ), and turns off the switch until the next switching cycle

begins.

THERMAL SHUTDOWN

Thermal shutdown limits total power dissipation by turning off

the output switch when the IC junction temperature exceeds

165°C. After thermal shutdown occurs, the output switch

doesn’t turn on until the junction temperature drops to ap-

proximately 150°C.

Design Guide

INDUCTOR SELECTION

The Duty Cycle (D) can be approximated quickly using the

ratio of output voltage (VO) to input voltage (VIN):

The catch diode (D1) forward voltage drop and the voltage

drop across the internal NMOS must be included to calculate

a more accurate duty cycle. Calculate D by using the following

formula:

VSW can be approximated by:

VSW = IO x RDS(ON)

The diode forward drop (VD) can range from 0.3V to 0.7V de-

pending on the quality of the diode. The lower VD is, the higher

the operating efficiency of the converter.

The inductor value determines the output ripple current. Low-

er inductor values decrease the size of the inductor, but

increase the output ripple current. An increase in the inductor

value will decrease the output ripple current. The ratio of ripple

current (ΔiL) to output current (IO) is optimized when it is set

between 0.3 and 0.4 at 750mA. The ratio r is defined as:

One must also ensure that the minimum current limit (1.0A)

is not exceeded, so the peak current in the inductor must be

calculated. The peak current (ILPK) in the inductor is calculated

by:

ILPK = IO + ΔIL/2

If r = 0.7 at an output of 750mA, the peak current in the in-

ductor will be 1.0125A. The minimum guaranteed current limit

over all operating conditions is 1.0A. One can either reduce r

to 0.6 resulting in a 975mA peak current, or make the engi-

neering judgement that 12.5mA over will be safe enough with

a 1.5A typical current limit and 6 sigma limits. When the de-

signed maximum output current is reduced, the ratio r can be

increased. At a current of 0.1A, r can be made as high as 0.9.

The ripple ratio can be increased at lighter loads because the

net ripple is actually quite low, and if r remains constant the

inductor value can be made quite large. An equation empiri-

cally developed for the maximum ripple ratio at any current

below 2A is:

r = 0.387 x IOUT-0.3667

Note that this is just a guideline.

The LM2736 operates at frequencies allowing the use of ce-

ramic output capacitors without compromising transient re-

sponse. Ceramic capacitors allow higher inductor ripple

without significantly increasing output ripple. See the output

capacitor section for more details on calculating output volt-

age ripple.

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LM2736

Now that the ripple current or ripple ratio is determined, the

inductance is calculated by:

where fs is the switching frequency and IO is the output cur-

rent. When selecting an inductor, make sure that it is capable

of supporting the peak output current without saturating. In-

ductor saturation will result in a sudden reduction in induc-

tance and prevent the regulator from operating correctly.

Because of the speed of the internal current limit, the peak

current of the inductor need only be specified for the required

maximum output current. For example, if the designed maxi-

mum output current is 0.5A and the peak current is 0.7A, then

the inductor should be specified with a saturation current limit

of >0.7A. There is no need to specify the saturation or peak

current of the inductor at the 1.5A typical switch current limit.

The difference in inductor size is a factor of 5. Because of the

operating frequency of the LM2736, ferrite based inductors

are preferred to minimize core losses. This presents little re-

striction since the variety of ferrite based inductors is huge.

Lastly, inductors with lower series resistance (DCR) will pro-

vide better operating efficiency. For recommended inductors

see Example Circuits.

INPUT CAPACITOR

An input capacitor is necessary to ensure that VIN does not

drop excessively during switching transients. The primary

specifications of the input capacitor are capacitance, voltage,

RMS current rating, and ESL (Equivalent Series Inductance).

The recommended input capacitance is 10µF, although 4.7µF

works well for input voltages below 6V. The input voltage rat-

ing is specifically stated by the capacitor manufacturer. Make

sure to check any recommended deratings and also verify if

there is any significant change in capacitance at the operating

input voltage and the operating temperature. The input ca-

pacitor maximum RMS input current rating (IRMS-IN) must be

greater than:

It can be shown from the above equation that maximum RMS

capacitor current occurs when D = 0.5. Always calculate the

RMS at the point where the duty cycle, D, is closest to 0.5.

The ESL of an input capacitor is usually determined by the

effective cross sectional area of the current path. A large

leaded capacitor will have high ESL and a 0805 ceramic chip

capacitor will have very low ESL. At the operating frequencies

of the LM2736, certain capacitors may have an ESL so large

that the resulting impedance (2πfL) will be higher than that

required to provide stable operation. As a result, surface

mount capacitors are strongly recommended. Sanyo

POSCAP, Tantalum or Niobium, Panasonic SP or Cornell

Dubilier ESR, and multilayer ceramic capacitors (MLCC) are

all good choices for both input and output capacitors and have

very low ESL. For MLCCs it is recommended to use X7R or

X5R dielectrics. Consult capacitor manufacturer datasheet to

see how rated capacitance varies over operating conditions.

OUTPUT CAPACITOR

The output capacitor is selected based upon the desired out-

put ripple and transient response. The initial current of a load

transient is provided mainly by the output capacitor. The out-

put ripple of the converter is:

When using MLCCs, the ESR is typically so low that the ca-

pacitive ripple may dominate. When this occurs, the output

ripple will be approximately sinusoidal and 90° phase shifted

from the switching action. Given the availability and quality of

MLCCs and the expected output voltage of designs using the

LM2736, there is really no need to review any other capacitor

technologies. Another benefit of ceramic capacitors is their

ability to bypass high frequency noise. A certain amount of

switching edge noise will couple through parasitic capaci-

tances in the inductor to the output. A ceramic capacitor will

bypass this noise while a tantalum will not. Since the output

capacitor is one of the two external components that control

the stability of the regulator control loop, most applications will

require a minimum at 10 µF of output capacitance. Capaci-

tance can be increased significantly with little detriment to the

regulator stability. Like the input capacitor, recommended

multilayer ceramic capacitors are X7R or X5R. Again, verify

actual capacitance at the desired operating voltage and tem-

perature.

Check the RMS current rating of the capacitor. The RMS cur-

rent rating of the capacitor chosen must also meet the follow-

ing condition:

CATCH DIODE

The catch diode (D1) conducts during the switch off-time. A

Schottky diode is recommended for its fast switching times

and low forward voltage drop. The catch diode should be

chosen so that its current rating is greater than:

ID1 = IO x (1-D)

The reverse breakdown rating of the diode must be at least

the maximum input voltage plus appropriate margin. To im-

prove efficiency choose a Schottky diode with a low forward

voltage drop.

BOOST DIODE

A standard diode such as the 1N4148 type is recommended.

For VBOOST circuits derived from voltages less than 3.3V, a

small-signal Schottky diode is recommended for greater effi-

ciency. A good choice is the BAT54 small signal diode.

BOOST CAPACITOR

A ceramic 0.01µF capacitor with a voltage rating of at least

6.3V is sufficient. The X7R and X5R MLCCs provide the best

performance.

OUTPUT VOLTAGE

The output voltage is set using the following equation where

R2 is connected between the FB pin and GND, and R1 is

connected between VO and the FB pin. A good value for R2

is 10kΩ.

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LM2736

PCB Layout Considerations

When planning layout there are a few things to consider when

trying to achieve a clean, regulated output. The most impor-

tant consideration when completing the layout is the close

coupling of the GND connections of the CIN capacitor and the

catch diode D1. These ground ends should be close to one

another and be connected to the GND plane with at least two

through-holes. Place these components as close to the IC as

possible. Next in importance is the location of the GND con-

nection of the COUT capacitor, which should be near the GND

connections of CIN and D1.

There should be a continuous ground plane on the bottom

layer of a two-layer board except under the switching node

island.

The FB pin is a high impedance node and care should be

taken to make the FB trace short to avoid noise pickup and

inaccurate regulation. The feedback resistors should be

placed as close as possible to the IC, with the GND of R2

placed as close as possible to the GND of the IC. The VOUT

trace to R1 should be routed away from the inductor and any

other traces that are switching.

High AC currents flow through the VIN, SW and VOUT traces,

so they should be as short and wide as possible. However,

making the traces wide increases radiated noise, so the de-

signer must make this trade-off. Radiated noise can be de-

creased by choosing a shielded inductor.

The remaining components should also be placed as close

as possible to the IC. Please see Application Note AN-1229

for further considerations and the LM2736 demo board as an

example of a four-layer layout.

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LM2736

LM2736X Circuit Examples

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FIGURE 6. LM2736X (1.6MHz)

VBOOST Derived from VIN

5V to 1.5V/750mA

Bill of Materials for Figure 6

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736X National Semiconductor

C1, Input Cap 10µF, 6.3V, X5R C3216X5ROJ106M TDK

C2, Output Cap 10µF, 6.3V, X5R C3216X5ROJ106M TDK

C3, Boost Cap 0.01uF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.3VF Schottky 1A, 10VR MBRM110L ON Semi

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

L1 4.7µH, 1.7A, VLCF4020T- 4R7N1R2 TDK

R1 2kΩ, 1% CRCW06032001F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

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LM2736

20124243

FIGURE 7. LM2736X (1.6MHz)

VBOOST Derived from VOUT

12V to 3.3V/750mA

Bill of Materials for Figure 7

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736X National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.34VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 30V, 200 mA Schottky BAT54 Diodes Inc.

L1 4.7µH, 1.7A, VLCF4020T- 4R7N1R2 TDK

R1 16.5kΩ, 1% CRCW06031652F Vishay

R2 10.0 kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

13 www.national.com

LM2736

20124244

FIGURE 8. LM2736X (1.6MHz)

VBOOST Derived from VSHUNT

18V to 1.5V/750mA

Bill of Materials for Figure 8

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736X National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

C4, Shunt Cap 0.1µF, 6.3V, X5R C1005X5R0J104K TDK

D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 5.1V 250Mw SOT-23 BZX84C5V1 Vishay

L1 6.8µH, 1.6A, SLF7032T-6R8M1R6 TDK

R1 2kΩ, 1% CRCW06032001F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

R4 4.12kΩ, 1% CRCW06034121F Vishay

www.national.com 14

LM2736

20124249

FIGURE 9. LM2736X (1.6MHz)

VBOOST Derived from Series Zener Diode (VIN)

15V to 1.5V/750mA

Bill of Materials for Figure 9

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736X National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 11V 350Mw SOT-23 BZX84C11T Diodes, Inc.

L1 6.8µH, 1.6A, SLF7032T-6R8M1R6 TDK

R1 2kΩ, 1% CRCW06032001F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

15 www.national.com

LM2736

20124250

FIGURE 10. LM2736X (1.6MHz)

VBOOST Derived from Series Zener Diode (VOUT)

15V to 9V/750mA

Bill of Materials for Figure 10

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736X National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 16V, X5R C3216X5R1C226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 4.3V 350mw SOT-23 BZX84C4V3 Diodes, Inc.

L1 6.8µH, 1.6A, SLF7032T-6R8M1R6 TDK

R1 61.9kΩ, 1% CRCW06036192F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

www.national.com 16

LM2736

LM2736Y Circuit Examples

20124242

FIGURE 11. LM2736Y (550kHz)

VBOOST Derived from VIN

5V to 1.5V/750mA

Bill of Materials for Figure 11

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736Y National Semiconductor

C1, Input Cap 10µF, 6.3V, X5R C3216X5ROJ106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.3VF Schottky 1A, 10VR MBRM110L ON Semi

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

L1 10µH, 1.6A, SLF7032T-100M1R4 TDK

R1 2kΩ, 1% CRCW06032001F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

17 www.national.com

LM2736

20124243

FIGURE 12. LM2736Y (550kHz)

VBOOST Derived from VOUT

12V to 3.3V/750mA

Bill of Materials for Figure 12

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736Y National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.34VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 30V, 200 mA Schottky BAT54 Diodes Inc.

L1 10µH, 1.6A, SLF7032T-100M1R4 TDK

R1 16.5kΩ, 1% CRCW06031652F Vishay

R2 10.0 kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

www.national.com 18

LM2736

20124244

FIGURE 13. LM2736Y (550kHz)

VBOOST Derived from VSHUNT

18V to 1.5V/750mA

Bill of Materials for Figure 13

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736Y National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

C4, Shunt Cap 0.1µF, 6.3V, X5R C1005X5R0J104K TDK

D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 5.1V 250Mw SOT-23 BZX84C5V1 Vishay

L1 15µH, 1.5A SLF7045T-150M1R5 TDK

R1 2kΩ, 1% CRCW06032001F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

R4 4.12kΩ, 1% CRCW06034121F Vishay

19 www.national.com

LM2736

20124249

FIGURE 14. LM2736Y (550kHz)

VBOOST Derived from Series Zener Diode (VIN)

15V to 1.5V/750mA

Bill of Materials for Figure 14

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736Y National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 11V 350Mw SOT-23 BZX84C11T Diodes, Inc.

L1 15µH, 1.5A, SLF7045T-150M1R5 TDK

R1 2kΩ, 1% CRCW06032001F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

www.national.com 20

LM2736

20124250

FIGURE 15. LM2736Y (550kHz)

VBOOST Derived from Series Zener Diode (VOUT)

15V to 9V/750mA

Bill of Materials for Figure 15

Part ID Part Value Part Number Manufacturer

U1 750mA Buck Regulator LM2736Y National Semiconductor

C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK

C2, Output Cap 22µF, 16V, X5R C3216X5R1C226M TDK

C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 4.3V 350mw SOT-23 BZX84C4V3 Diodes, Inc.

L1 22µH, 1.4A, SLF7045T-220M1R3-1PF TDK

R1 61.9kΩ, 1% CRCW06036192F Vishay

R2 10kΩ, 1% CRCW06031002F Vishay

R3 100kΩ, 1% CRCW06031003F Vishay

21 www.national.com

LM2736

Physical Dimensions inches (millimeters) unless otherwise noted

6-Lead TSOT Package

NS Package Number MK06A

www.national.com 22

LM2736

Notes

23 www.national.com

LM2736

Notes

LM2736 Thin SOT23 750mA Load Step-Down DC-DC Regulator

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