Texas Instruments LM2734XMK, LM2734XQMK, LM2734YMK, LM2734YQMK Schematic [ru]

LM2734

VIN

VIN

EN

BOOST

SW

FB

GND

V

OUT

C3

L1

C1

C2

R1

R2

D1

D2

ON

OFF

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SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

LM2734 Thin SOT 1-A Load Step-Down DC-DC Regulator

1 Features 3 Description

1

• Thin SOT-6 Package

• 3.0-V to 20-V Input Voltage Range

• 0.8-V to 18-V Output Voltage Range

• 1-A Output Current

• 550-kHz (LM2734Y) and 1.6-MHz (LM2734X)
Switching Frequencies

• 300-mΩ NMOS Switch

• 30-nA Shutdown Current

• 0.8-V, 2% Internal Voltage Reference

• Internal Soft-Start

• Current-Mode, PWM Operation

• WEBENCH®Online Design Tool

• Thermal Shutdown

• LM2734XQ and LM2734YQ are AEC-Q100 Grade
1 Qualified and are Manufactured on an
Automotive Grade Flow.

2 Applications

• Local Point-of-Load Regulation

• Core Power in HDDs

• Set-Top Boxes

• Battery-Powered Devices

• USB Powered Devices

• DSL Modems

• Notebook Computers

• Automotive

Typical Application Circuit

The LM2734 regulator is a monolithic, high­frequency, PWM step-down DC-DC converter in a 6­pin Thin SOT package. The device 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 LM2734
regulator is easy to use. The ability to drive 1-A loads
with an internal 300-mΩ NMOS switch using state-of­the-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 20-V input operating range
down to the minimum output voltage of 0.8 V.
Switching frequency is internally set to 550 kHz
(LM2734Y) or 1.6 MHz (LM2734X), 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 standby current of 30 nA.

The LM2734 regulator uses current-mode control and
internal 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 overvoltage protection.

Device Information

PART NUMBER PACKAGE BODY SIZE (NOM)

LM2734 SOT (6) 2.90 mm x 1.60 mm
(1) For all available packages, see the orderable addendum at

the end of the datasheet.

Efficiency vs Load Current

VIN= 5 V, V

OUT

LM2734

(1)

= 3.3 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.

LM2734

SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

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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 Performance 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................................................ 14

9 Power Supply Recommendations...................... 28

10 Layout................................................................... 28

10.1 Layout Guidelines................................................. 28

10.2 Layout Example.................................................... 29

11 Device and Documentation Support................. 30

11.1 Third-Party Products Disclaimer........................... 30

11.2 Trademarks........................................................... 30

11.3 Electrostatic Discharge Caution............................ 30

11.4 Glossary................................................................ 30

12 Mechanical, Packaging, and Orderable

Information........................................................... 30

4 Revision History

Changes from Revision I (April 2013) to Revision J 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.................................................................................................. 1

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1

2

3

6

5

4

BOOST

GND

FB

SW

V

IN

EN

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5 Pin Configuration and Functions

LM2734

SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

See Package Number 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.

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6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature (unless otherwise noted)

V

IN

SW Voltage -0.5 24 V
Boost Voltage -0.5 30 V
Boost to SW Voltage -0.5 6.0 V
FB Voltage -0.5 0.3 V
EN Voltage -0.5 VIN+ 0.3 V
Junction Temperature 150 °C
Soldering Information Reflow Peak Pkg. Temp.(15s) 260 °C
T

Storage temperature -65 150 °C

stg

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) 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 Human Body Model (HBM), per ANSI/ESDA/JEDEC JS001

ESD

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

(1)(2)

MIN MAX UNIT

-0.5 24 V

VALUE UNIT

(1)

±2000 V

6.3 Recommended Operating Conditions

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

MIN NOM MAX UNIT

V

IN

SW Voltage -0.5 20 V
Boost Voltage -0.5 25 V
Boost to SW Voltage 1.6 5.5 V
Junction Temperature Range −40 125 °C

3 20 V

6.4 Thermal Information

LM2734

THERMAL METRIC

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.

(1)

DDC UNIT

6 PINS

°C/W

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6.5 Electrical Characteristics

VIN= 5V, V
statistical analysis.

V
ΔVFB/Δ Feedback Voltage Line VIN= 3V to 20V

V
I

FB

UVLO Undervoltage Lockout VINFalling 2.3 2.0 V

F

D

D

R
I

CL

I

Q

I

BOOST

V

I

EN

I

SW

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

Feedback Voltage 0.800 0.784 0.816 V

FB

Regulation

IN

Feedback Input Bias Sink/Source
Current

Undervoltage Lockout VINRising 2.74 2.90

UVLO Hysteresis 0.44 0.30 0.62

Switching Frequency MHz

SW

Maximum Duty Cycle

MAX

Minimum Duty Cycle

MIN

Switch ON Resistance V

DS(ON)

Switch Current Limit V
Quiescent Current Switching 1.5 2.5 mA
Quiescent Current VEN= 0V

(shutdown)

Boost Pin Current mA

Shutdown Threshold VENFalling
Voltage

EN_TH

Enable Threshold VENRising 1.8
Voltage

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

- VSW= 5V unless otherwise specified. Datasheet min/max specification limits are ensured by design, test, or

BOOST

PARAMETER TEST CONDITIONS UNIT

MIN

TJ= 25°C TJ= -40°C to 125°C

(1)

TYP

(2)

MAX

(1)

MIN TYP MAX

0.01 % / V

10 250 nA

LM2734X 1.6 1.2 1.9
LM2734Y 0.55 0.40 0.66
LM2734X 92 85%
LM2734Y 96 90%
LM2734X 2%
LM2734Y 1%

- VSW= 3V 300 600 mΩ

BOOST

- VSW= 3V 1.7 1.2 2.5 A

BOOST

30 nA

LM2734X (50% Duty
Cycle)

LM2734Y (50% Duty
Cycle)

2.5 3.5

1.0 1.8

0.4
V

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SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

6.6 Typical Performance Characteristics

All curves taken at VIN= 5 V, V

Figure 1. Oscillator Frequency vs Temperature - L1 = 4.7 µH Figure 2. Oscillator Frequency vs Temperature - L1 = 10 μH

- VSW= 5 V and TA= 25°C, unless specified otherwise.

BOOST

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

VIN= 20 V

Figure 5. VFBvs Temperature Figure 6. R

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vs Temperature

DSON

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Typical Performance Characteristics (continued)

LM2734

SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

All curves taken at VIN= 5 V, V

Figure 7. IQSwitching vs Temperature Figure 8. Line Regulation - L1 = 4.7 µH

- VSW= 5 V and TA= 25°C, unless specified otherwise.

BOOST

V

OUT

= 1.5 V, I

OUT

= 500 mA

Figure 9. Line Regulation - L1 = 10 μH Figure 10. Line Regulation - L1 = 4.7 µH

V

OUT

= 1.5 V, I

= 500 mA V

OUT

OUT

= 3.3 V, I

OUT

= 500 mA

Figure 11. Line Regulation - L1 = 10 μH

V

= 3.3 V, I

OUT

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OUT

= 500 mA

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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

LM2734

SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

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7 Detailed Description

7.1 Overview

The LM2734 device is a constant frequency PWM buck regulator IC that delivers a 1-A load current. The
regulator has a preset switching frequency of either 550 kHz (LM2734Y) or 1.6 MHz (LM2734X). These high
frequencies allow the LM2734 device to operate with small surface-mount capacitors and inductors, resulting in
DC-DC converters that require a minimum amount of board space. The LM2734 device is internally
compensated, so it is simple to use, and requires few external components. The LM2734 device uses current­mode control to regulate the output voltage.

The following operating description of the LM2734 device will refer to the Simplified Block Diagram () and to the
waveforms in Figure 12. The LM2734 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
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 output switch turns off until the

REF

Figure 12. LM2734 Waveforms of SW Pin Voltage and Inductor Current

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L

R
1

R
2

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

0.8V

C

OUT

ON

OFF

V

BOOST

I

L

V

SW

+

-

C

BOOST

V

OUT

C

IN

V

IN

V

IN

I

SENSE

+

-

+

-

+

-

0.88V

-

+

OVP

Comparator

Error

Signal

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7.2 Functional Block Diagram

LM2734

SNVS288J –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 LM2734 from operating until the input voltage exceeds 2.74 V
(typical).

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

7.3.3 Current Limit

The LM2734 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 1.7 A (typical), 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 does not 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 LM2734 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 0.8 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. Under some
circumstances at start-up, an output voltage overshoot may still be observed. This may be due to a large output
load applied during start up. Large amounts of output external capacitance can also increase output voltage
overshoot. A simple solution is to add a feed forward capacitor with a value between 470 pf and 1000 pf across
the top feedback resistor (R1). See Figure 23 for further detail.

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

OUT

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LM2734

BOOST

SW

GND

L

D1

D2

C

OUT

C

BOOST

V

OUT

C

IN

V

IN

V

IN

V

BOOST

LM2734

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SNVS288J –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 LM2734 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 13 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 13. V

Charges C

OUT

BOOST

When the LM2734 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 0.76 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 simplified block diagram of Functional Block Diagram, capacitor C
drive current for the NMOS switch. Capacitor C
cycle, when the internal NMOS control switch is off (T
forward voltage of D2 (V
(V

). Therefore the voltage stored across C

FD1

V

- VSW= VIN- V

BOOST

), during which the current in the inductor (L) forward biases the Schottky diode D1

FD2

BOOST

+ V

FD2

FD1

is charged via diode D2 by VIN. During a normal switching

BOOST

) (refer to Figure 12), V

OFF

is:

and diode D2 supply the gate-

BOOST

equals VINminus the

BOOST

(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:

2VIN- 0.4 V (4)

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× IL), (2)

DSON

is then:

BOOST

DSON

× IL) – V

+ V

FD2

FD1

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(3)

LM2734

V

IN

BOOST

SW

GND

C

BOOST

L

D1

D2

D3

C

IN

V

IN

C

OUT

V

OUT

V

BOOST

LM2734

SNVS288J –SEPTEMBER 2004–REVISED DECEMBER 2014

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Application Information (continued)

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

VIN- 0.2 V (5)

An alternate method for charging C
voltage should be from 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 VINto V
a Zener voltage by placing a Zener diode D3 in series with D2, as shown in Figure 14. When using a series
Zener diode from the input, ensure that the regulation of the input supply does not 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 13. 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

can be charged from VINor V

BOOST

cannot be charged

BOOST

OUT

minus

Figure 14. 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 15. A small 350
mW to 500 mW 5.1-V Zener diode 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

= 0.56 × (D + 0.54) × (V

BOOST

I

can be calculated for the Y version using the following:

BOOST

I

= 0.22 × (D + 0.54) × (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 × 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 × I

BOOST

+ I

) (11)

ZENER

= 5 V, VD2= 0.7 V, I

ZENER

= 1 mA, and duty cycle D =

ZENER

50%. Then:

I

= 0.56 × (0.5 + 0.54) × (5 - 0.7) mA = 2.5 mA (12)

BOOST

R3 = (10 V - 5 V) / (1.4 × 2.5 mA + 1 mA) = 1.11 kΩ (13)

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