Texas Instruments LM2736XMK, LM2736YMK Schematic [ru]

VIN

VIN

EN

BOOST

SW

FB

GND

V

OUT

C3

L1

C1

C2

R1

R2

D1

D2

ON

OFF

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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

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

1 Features 3 Description

1

• Thin SOT-6 Package

• 3.0 V to 18 V Input Voltage Range

• 1.25 V to 16 V Output Voltage Range

• 750 mA Output Current

• 550 kHz (LM2736Y) and 1.6 MHz (LM2736X)
Switching Frequencies

• 350 mΩ NMOS Switch

• 30 nA Shutdown Current

• 1.25 V, 2% Internal Voltage Reference

• Internal Soft-Start

• Current-Mode, PWM Operation

• WEBENCH®Online Design Tool

• Thermal Shutdown

2 Applications

• Local Point of Load Regulation

• Core Power in HDDs

• Set-Top Boxes

• Battery Powered Devices

• USB Powered Devices

• DSL Modems

• Notebook Computers

The LM2736 regulator is a monolithic, high frequency,
PWM step-down DC/DC converter in a 6-pin Thin
SOT package. It provides all the active functions to
provide local DC/DC conversion with fast transient
response and accurate regulation 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 750 mA loads with an
internal 350 mΩ NMOS switch using state-of-the-art

0.5 µm BiCMOS technology results in the best power
density available. The world class control circuitry
allows for on-times as low as 13 ns, thus supporting
exceptionally high frequency conversion over the
entire 3 V to 18 V input operating range down to the
minimum output voltage of 1.25 V. Switching
frequency is internally set to 550 kHz (LM2736Y) or

1.6 MHz (LM2736X), allowing the use of extremely
small surface mount inductors and chip capacitors.
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 30 nA. The LM2736 utilizes current-mode
control and internal compensation to provide high­performance 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.

LM2736

Device Information

PART NUMBER PACKAGE BODY SIZE (NOM)

LM2736 SOT (6) 2.90 mm x 1.60 mm
(1) For all available packages, see the orderable addendum at

the end of the datasheet.

(1)

Typical Application Circuit

Efficiency vs. Load Current "X"

VIN= 5 V, V

1

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.

OUT

= 3.3 V

LM2736

SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

www.ti.com

Table of Contents

1 Features.................................................................. 1

2 Applications ........................................................... 1

3 Description ............................................................. 1

4 Revision History..................................................... 2

5 Pin Configuration and Functions......................... 3

6 Specifications......................................................... 4

6.1 Absolute Maximum Ratings ...................................... 4

6.2 ESD Ratings ............................................................ 4

6.3 Recommended Operating Conditions....................... 4

6.4 Thermal Information.................................................. 4

6.5 Electrical Characteristics........................................... 5

6.6 Typical Characteristics.............................................. 6

7 Detailed Description .............................................. 8

7.1 Overview................................................................... 8

7.2 Functional Block Diagram......................................... 9

7.3 Feature Description................................................... 9

7.4 Device Functional Modes........................................ 10

8 Application and Implementation ........................ 11

8.1 Application Information .......................................... 11

8.2 Typical Applications ............................................... 13

9 Power Supply Recommendations...................... 27

10 Layout................................................................... 27

10.1 Layout Guidelines ................................................. 27

10.2 Layout Example .................................................... 28

11 Device and Documentation Support ................. 29

11.1 Device Support...................................................... 29

11.2 Documentation Support ........................................ 29

11.3 Trademarks........................................................... 29

11.4 Electrostatic Discharge Caution............................ 29

11.5 Glossary................................................................ 29

12 Mechanical, Packaging, and Orderable

Information........................................................... 29

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision G (October 2014) to Revision H Page

• Updated Design Requirements and moved Bill of Materials to Detailed Design Procedures.............................................. 13

Changes from Revision F (April 2013) to Revision G Page

• Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and

Mechanical, Packaging, and Orderable Information section.................................................................................................. 4

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1

2

3

6

5

4

BOOST

GND

FB

SW

V

IN

EN

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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

5 Pin Configuration and Functions

Package DDC (R-PDSO-G6)

6-Lead SOT

Top View

Pin Functions

PIN

NAME NO.

BOOST 1 I

GND 2 GND
FB 3 I Feedback pin. Connect FB to the external resistor divider to set output voltage.
EN 4 I
V

IN

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

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

I/O DESCRIPTION

Boost voltage that drives the internal NMOS control switch. A bootstrap capacitor is
connected between the BOOST and SW pins.

Signal and Power ground pin. Place the bottom resistor of the feedback network as close as
possible to this pin for accurate regulation.

Enable control input. Logic high enables operation. Do not allow this pin to float or be greater
than VIN+ 0.3 V.

LM2736

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6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)

V

IN

SW Voltage -0.5 22 V
Boost Voltage -0.5 28 V
Boost to SW Voltage -0.5 8 V
FB Voltage -0.5 3 V
EN Voltage -0.5 VIN+ 0.3 V
Junction Temperature 150 °C

Soldering
Information

T

stg

Infrared/Convection Reflow (15sec) 220 °C
Wave Soldering Lead temperature (10sec) 260 °C
Storage temperature -65 150 °C

(1) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and

specifications.

6.2 ESD Ratings

V

Electrostatic discharge ±2000 V

(ESD)

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

Human body model (HBM),
per ANSI/ESDA/JEDEC JS-001, all pins

(1)

MIN MAX UNIT

-0.5 22 V

VALUE UNIT

(1)

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)

MIN NOM MAX UNIT

V

IN

SW Voltage -0.5 18 V
Boost Voltage -0.5 23 V
Boost to SW Voltage 1.6 5.5 V
Junction Temperature Range −40 125 °C

3 18 V

6.4 Thermal Information

LM2736

THERMAL METRIC

(2)

R

θJA

R

θJC(top)

R

θJB

ψ

JT

ψ

JB

R

θJC(bot)

Junction-to-ambient thermal resistance 158.1
Junction-to-case (top) thermal resistance 46.5
Junction-to-board thermal resistance 29.5
Junction-to-top characterization parameter 0.8
Junction-to-board characterization parameter 29.2
Junction-to-case (bottom) thermal resistance n/a

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
(2) Thermal shutdown will occur if the junction temperature exceeds 165°C. The maximum power dissipation is a function of T

and TA. The maximum allowable power dissipation at any ambient temperature is PD= (T
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.

(1)

DDC UNIT

6 PINS

°C/W

– TA)/θJA. All numbers apply for

J(MAX)

J(MAX)

, θ

JA

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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

6.5 Electrical Characteristics

Specifications with standard typeface are for TJ= 25°C unless otherwise specified. Datasheet min/max specification limits are
ensured by design, test, or statistical analysis.

PARAMETER TEST CONDITIONS UNIT

V

Feedback Voltage 1.250 1.225 1.275 V

FB

MIN

ΔVFB/Δ Feedback Voltage Line VIN= 3V to 18V
V

I

FB

Regulation

IN

Feedback Input Bias
Current

Sink/Source 10 250 nA

Undervoltage Lockout VINRising 2.74 2.90

UVLO Undervoltage Lockout VINFalling 2.3 2.0 V

UVLO Hysteresis 0.44 0.30 0.62

F

SW

D

MAX

D

MIN

R

DS(ON)

I

CL

I

Q

Switching Frequency MHz

Maximum Duty Cycle

Minimum Duty Cycle

Switch ON Resistance V
Switch Current Limit V
Quiescent Current Switching 1.5 2.5 mA

LM2736X 1.6 1.2 1.9
LM2736Y 0.55 0.40 0.66
LM2736X 92% 85%
LM2736Y 96% 90%
LM2736X 2%
LM2736Y 1%

- VSW= 3V 350 650 mΩ

BOOST

- VSW= 3V 1.5 1.0 2.3 A

BOOST

Quiescent Current VEN= 0V
(shutdown)

LM2736X (50% Duty

I

BOOST

Boost Pin Current mA

Cycle)
LM2736Y (50% Duty

Cycle)

Shutdown Threshold VENFalling

V

Voltage

EN_TH

Enable Threshold VENRising 1.8
Voltage

I

EN

I

SW

Enable Pin Current Sink/Source 10 nA
Switch Leakage 40 nA

(1) Specified to Texas Instruments' Average Outgoing Quality Level (AOQL).
(2) Typicals represent the most likely parametric norm.

TJ= 25°C TJ = -40°C to 125°C

(1)

TYP

(2)

MAX

(1)

MIN TYP MAX

0.01 % / V

30 nA

2.2 3.3

0.9 1.6

0.4
V

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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

6.6 Typical Characteristics

All curves taken at VIN= 5V, V
otherwise.

Figure 1. Oscillator Frequency vs Temperature - "X" Figure 2. Oscillator Frequency vs Temperature - "Y"

- VSW= 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified

BOOST

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Figure 3. Current Limit vs Temperature Figure 4. VFBvs Temperature

Figure 5. R

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vs Temperature Figure 6. IQSwitching vs Temperature

DSON

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Typical Characteristics (continued)

LM2736

SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

All curves taken at VIN= 5V, V
otherwise.

Figure 7. Line Regulation - "X" Figure 8. Line Regulation - "Y"

- VSW= 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified

BOOST

V

OUT

= 3.3 V, I

= 500 mA V

OUT

OUT

= 3.3 V, I

OUT

= 500 mA

Figure 9. Line Regulation - "X" Figure 10. Line Regulation - "Y"

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0

0

V

IN

V

D

T

ON

t

t

Inductor

Current

D = TON/T

SW

V

SW

T

OFF

T

SW

I

L

I

PK

SW

Voltage

LM2736

SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

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7 Detailed Description

7.1 Overview

The LM2736 device is a constant frequency PWM buck regulator IC that delivers a 750 mA load current. The
regulator has a preset switching frequency of either 550 kHz (LM2736Y) or 1.6 MHz (LM2736X). These high
frequencies allow the LM2736 device to operate with small surface mount capacitors and inductors, resulting in
DC/DC converters that require a minimum amount of board space. The LM2736 device is internally
compensated, so it is simple to use, and requires few external components. The LM2736 device uses current­mode control to regulate the output voltage.

The following operating description of the LM2736 device will refer to the Simplified Block Diagram (Functional

Block Diagram) and to the waveforms in Figure 11. The LM2736 device supplies a regulated output voltage by

switching the internal NMOS control switch at constant 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 control logic turns on the internal NMOS control switch. During this on-time, the SW pin voltage (VSW)
swings up to approximately VIN, and the inductor current (IL) increases with a linear slope. ILis 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 proportional
to the difference between the feedback voltage and V
output 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.

. When the PWM comparator output goes high, the

REF

Figure 11. LM2736 Waveforms of SW Pin Voltage and Inductor Current

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L

R1

R2

D
1

D2

BOOST

Output
Control

Logic

Current

Limit

Thermal

Shutdown

Under
Voltage
Lockout

Corrective Ramp

Reset
Pulse

PWM

Comparator

Current-Sense Amplifier

R

SENSE

+

+

Internal

Regulator

and

Enable

Circuit

Oscillator

Driver

0.3:

Switch

Internal

Compensation

SW

EN

FB

GND

Error Amplifier

-

+

V

REF

1.25V

C

OUT

ON

OFF

V

BOOST

V

SW

+

-

C

BOOST

V

OUT

C

IN

V

IN

V

IN

I

SENSE

+

-

+

-

+

-

1.375V

OVP

Comparator

Error

Signal

-

+

I

L

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7.2 Functional Block Diagram

LM2736

SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

7.3 Feature Description

7.3.1 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 reference, the internal NMOS control
switch is turned off, which allows the output voltage to decrease toward regulation.

7.3.2 Undervoltage Lockout

Undervoltage lockout (UVLO) prevents the LM2736 device from operating until the input voltage exceeds 2.74 V
(typ).

The UVLO threshold has approximately 440mV of hysteresis, so the part will operate until VINdrops below 2.3 V
(typ). Hysteresis prevents the part from turning off during power up if VINis non-monotonic.

7.3.3 Current Limit

The LM2736 device 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 1.5 A (typ), and turns off the switch until
the next switching cycle begins.

7.3.4 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 approximately 150°C.

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7.4 Device Functional Modes

7.4.1 Enable Pin / Shutdown Mode

The LM2736 device 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 30 nA. Switch leakage
adds another 40 nA from the input supply. The voltage at this pin should never exceed VIN+ 0.3 V.

7.4.2 Soft-Start

This function forces V
reference voltage ramps from 0 V to its nominal value of 1.25 V in approximately 200 µs. This forces the
regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current.

to increase at a controlled rate during start up. During soft-start, the error amplifier’s

OUT

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BOOST

SW

GND

L

D1

D2

C

OUT

C

BOOST

V

OUT

C

IN

V

IN

V

IN

V

BOOST

LM2736

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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.

8.1 Application Information

8.1.1 Boost Function

Capacitor C
drive voltage to the internal NMOS control switch. To properly drive the internal NMOS switch during its on-time,
V

needs to be at least 1.6 V greater than VSW. Although the LM2736 device will operate with this minimum

BOOST

voltage, it may not have sufficient gate drive to supply large values of output current. Therefore, it is
recommended that V
the maximum operating limit of 5.5 V.

5.5 V > V

BOOST

and diode D2 in Figure 12 are used to generate a voltage V

BOOST

be greater than 2.5 V above VSWfor best efficiency. V

BOOST

– VSW> 2.5 V for best performance.

BOOST

BOOST

. V

- VSWis the gate

BOOST

– VSWshould not exceed

Figure 12. V

Charges C

OUT

BOOST

When the LM2736 device starts up, internal circuitry from the BOOST pin supplies a maximum of 20 mA to
C
source current to C

There are various methods to derive V

. This current charges C

BOOST

to a voltage sufficient to turn the switch on. The BOOST pin will continue to

BOOST

until the voltage at the feedback pin is greater than 1.18 V.

BOOST

:

BOOST

1. From the input voltage (VIN)

2. From the output voltage (V

3. From an external distributed voltage rail (V

OUT

)

)

EXT

4. From a shunt or series zener diode

In the Functional Block Diagram, capacitor C
switch. Capacitor C
NMOS control switch is off (T

is charged via diode D2 by VIN. During a normal switching cycle, when the internal

BOOST

) (refer to Figure 11), V

OFF

during which the current in the inductor (L) forward biases the Schottky diode D1 (V
stored across C

V

- VSW= VIN- V

BOOST

BOOST

is

+ V

FD2

FD1

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

BOOST

equals VINminus the forward voltage of D2 (V

BOOST

). Therefore the voltage

FD1

FD2

),

(1)

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

VSW= VIN– (R

forcing V

V

BOOST

to rise thus reverse biasing D2. The voltage at V

BOOST

= 2VIN– (R

which is approximately

2 VIN- 0.4 V (4)

for many applications. Thus the gate-drive voltage of the NMOS switch is approximately

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x IL), (2)

DSON

is then

BOOST

DSON

x IL) – V

FD2

+ V

FD1

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(3)

V

IN

BOOST

SW

GND

C

BOOST

L

D1

D2

D3

V

BOOST

V

IN

C

IN

C

OUT

V

OUT

LM2736

SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014

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Application Information (continued)

VIN- 0.2 V (5)

An alternate method for charging C
voltage should be between 2.5 V and 5.5 V, so that proper gate voltage will be applied to the internal switch. In
this circuit, C

provides a gate drive voltage that is slightly less than V

BOOST

In applications where both VINand V
directly from these voltages. If VINand V
minus a zener voltage by placing a zener diode D3 in series with D2, as shown in Figure 13. 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 V

(V
(V

– VD3) < 5.5 V (6)

INMAX

– VD3) > 1.6 V (7)

INMIN

BOOST

voltage.

is to connect D2 to the output as shown in Figure 12. The output

BOOST

.

OUT

are greater than 5.5 V, or less than 3 V, C

OUT

are greater than 5.5 V, C

OUT

BOOST

can be charged from VINor V

cannot be charged

BOOST

OUT

Figure 13. Zener Reduces Boost Voltage from V

IN

An alternative method is to place the zener diode D3 in a shunt configuration as shown in Figure 14. A small 350
mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic capacitor
such as a 6.3 V, 0.1 µF 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 capacitance. The 0.1 µF
parallel shunt capacitor ensures that the V

voltage is maintained during this time.

BOOST

Resistor R3 should be chosen to provide enough RMS current to the zener diode (D3) and to the BOOST pin. A
recommended choice for the zener current (I

) is 1 mA. The current I

ZENER

into the BOOST pin supplies the

BOOST

gate current of the NMOS control switch and varies typically according to the following formula for the X ­version:

I

= 0.49 x (D + 0.54) x (V

BOOST

I

can be calculated for the Y version using the following:

BOOST

I

= 0.20 x (D + 0.54) x (V

BOOST

where D is the duty cycle, V

ZENER

– VD2) mA (8)

ZENER

- VD2) µA (9)

ZENER

and VD2are in volts, and I

is in milliamps. V

BOOST

is the voltage applied to

ZENER

the anode of the boost diode (D2), and VD2is the average forward voltage across D2. Note that this formula for
I

gives typical current. For the worst case I

BOOST

, increase the current by 40%. In that case, the worst case

BOOST

boost current will be

I

BOOST-MAX

= 1.4 x I

BOOST

(10)

R3 will then be given by

R3 = (VIN- V

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

ZENER

) / (1.4 x I

BOOST

+ I

) (11)

ZENER

= 5 V, VD2= 0.7 V, I

ZENER

= 1 mA, and duty cycle D =

ZENER

50%. Then

I

= 0.49 x (0.5 + 0.54) x (5 - 0.7) mA = 2.19mA (12)

BOOST

R3 = (10 V - 5 V) / (1.4 x 2.19 mA + 1 mA) = 1.23 kΩ (13)

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