Linear LT1933ES6, LT1933HDCB, LT1933HS6, LT1933IDCB, LT1933IS6 Schematic [ru]

LT1933

600mA, 500kHz Step-Down

Switching Regulator in

SOT-23 and DFN Packages

FEATURES

n

Wide Input Range: 3.6V to 36V

n

5V at 600mA from 16V to 36V Input

n

3.3V at 600mA from 12V to 36V Input

n

5V at 500mA from 6.3V to 36V Input

n

3.3V at 500mA from 4.5V to 36V Input

n

Fixed Frequency 500kHz Operation

n

Uses Tiny Capacitors and Inductors

n

Soft-Start

n

Internally Compensated

n

Low Shutdown Current: <2µA

n

Output Adjustable Down to 1.25V

n

Low Profi le (1mm) SOT-23 (ThinSOT™) and

(2mm × 3mm × 0.75mm) 6-Pin DFN Packages

APPLICATIONS

n

Automotive Battery Regulation

n

Industrial Control Supplies

n

Wall Transformer Regulation

n

Distributed Supply Regulation

n

Battery-Powered Equipment

DESCRIPTION

The LT®1933 is a current mode PWM step-down DC/DC
converter with an internal 0.75A power switch, packaged
in a tiny 6-lead SOT-23. The wide input range of 3.6V
to 36V makes the LT1933 suitable for regulating power
from a wide variety of sources, including unregulated wall
transformers, 24V industrial supplies and automotive
batteries. Its high operating frequency allows the use of
tiny, low cost inductors and ceramic capacitors, resulting
in low, predictable output ripple.

Cycle-by-cycle current limit provides protection against
shorted outputs, and soft-start eliminates input current
surge during start up. The low current (<2µA) shutdown
provides output disconnect, enabling easy power manage­ment in battery-powered systems.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.

TYPICAL APPLICATION

3.3V Step-Down Converter

V

4.5V TO 36V

OFF ON

IN

V

IN

LT1933

SHDN SW

GND FB

2.2µF

BOOST

16.5k

10k

1N4148

0.1µF

MBRM140

22µH

V

OUT

3.3V/500mA

22µF

1933 TA01a

95

VIN = 12V

90

85

80

EFFICIENCY (%)

75

70

65

100 200 600500

0

Effi ciency

V

= 5V

OUT

V

= 3.3V

OUT

300 400

LOAD CURRENT (mA)

1933 TA01b

1933fe

1

LT1933

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Input Voltage (VIN) ..................................... –0.4V to 36V

BOOST Pin Voltage ...................................................43V

BOOST Pin Above SW Pin .........................................20V

SHDN Pin ................................................... –0.4V to 36V

FB Voltage .................................................... –0.4V to 6V

Operating Temperature Range (Note 2)

LT1933E ...................................................–40°C to 85°C

PIN CONFIGURATION

TOP VIEW

6

BOOST

V

SW

1

2

IN

3

7

FB

5

GND

SHDN

4

LT1933I .................................................. –40°C to 125°C

LT1933H ................................................–40°C to 150°C

Maximum Junction Temperature

LT1933E, LT1933I ................................................. 125°C

LT1933H ............................................................... 150°C

Storage Temperature Range ..................–65°C to 150°C

Lead Temperature, S6 Package

(Soldering, 10 sec) ............................................ 300°C

TOP VIEW

BOOST 1

GND 2

FB 3

6 SW

5 V

IN

4 SHDN

6-LEAD (2mm × 3mm) PLASTIC DFN

DCB PACKAGE

θJA = 73.5°C/W, θJC = 12°C/W

EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB

S6 PACKAGE

6-LEAD PLASTIC TSOT-23

θJA = 165°C/W, θJC = 102°C/W

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LT1933IDCB#PBF LT1933IDCB#TRPBF LCGM

LT1933HDCB#PBF LT1933HDCB#TRPBF LCGN

LT1933ES6#PBF LT1933ES6#TRPBF LTAGN 6-Lead Plastic TSOT-23 –40°C to 85°C

LT1933IS6#PBF LT1933IS6#TRPBF LTAGP 6-Lead Plastic TSOT-23 –40°C to 125°C

LT1933HS6#PBF LT1933HS6#TRPBF LTDDQ 6-Lead Plastic TSOT-23 –40°C to 150°C

LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LT1933IDCB LT1933IDCB#TR LCGM

LT1933HDCB LT1933HDCB#TR LCGN

LT1933ES6 LT1933ES6#TR LTAGN 6-Lead Plastic TSOT-23 –40°C to 85°C

LT1933IS6 LT1933IS6#TR LTAGP 6-Lead Plastic TSOT-23 –40°C to 125°C

LT1933HS6 LT1933HS6#TR LTDDQ 6-Lead Plastic TSOT-23 –40°C to 150°C

Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
For more information on lead free part marking, go to:

For more information on tape and reel specifi cations, go to:

http://www.linear.com/leadfree/

http://www.linear.com/tapeandreel/

6-Lead (2mm × 3mm) Plastic DFN

6-Lead (2mm × 3mm) Plastic DFN

6-Lead (2mm × 3mm) Plastic DFN

6-Lead (2mm × 3mm) Plastic DFN

–40°C to 125°C

–40°C to 150°C

–40°C to 125°C

–40°C to 150°C

2

1933fe

LT1933

ELECTRICAL CHARACTERISTICS

The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Undervoltage Lockout 3.35 3.6 V

Feedback Voltage

FB Pin Bias Current V

Quiescent Current Not Switching 1.6 2.5 mA

Quiescent Current in Shutdown V

Reference Line Regulation V

Switching Frequency V

Maximum Duty Cycle

Switch Current Limit (Note 3) 0.75 1.05 A

Switch V

CESAT

Switch Leakage Current 2µA

Minimum Boost Voltage Above Switch I

BOOST Pin Current I

SHDN Input Voltage High 2.3 V
SHDN Input Voltage Low 0.3 V
SHDN Bias Current V

FB

SHDN

IN

FB

V

FB

ISW = 400mA, S6 Package
I

SW

SW

SW

SHDN

V

SHDN

= 25°C. VIN = 12V, V

A

= Measured V

= 0V 0.01 2 µA

= 5V to 36V 0.01 %/V

= 1.1V 400 500 600 kHz

= 0V 55 kHz

= 400mA, DCB6 Package

= 400mA 1.9 2.3 V

= 400mA 18 25 mA

= 2.3V (Note 5)
= 0V

+ 10mV (Note 4)

REF

= 17V, unless otherwise noted. (Note 2)

BOOST

l

1.225 1.245 1.265 V

l

l

88 94 %

40 120 nA

370
370

34

0.01

500 mV

50

0.1

mV

µA
µA

Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.

Note 2: The LT1933E is guaranteed to meet performance specifi cations
from 0°C to 70°C. Specifi cations over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT1933I specifi cations are

guaranteed over the –40°C to 125°C temperature range. The LT1933H
specifi cations are guaranteed over the –40°C to 150°C temperature range.

Note 3: Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.

Note 4: Current fl ows out of pin.
Note 5: Current fl ows into pin.

1933fe

3

LT1933

TYPICAL PERFORMANCE CHARACTERISTICS

Effi ciency, V

100

TA = 25°C

= 5V

V

OUT

90

80

EFFICIENCY (%)

70

60

100 200 600500

0

= 5V Effi ciency, V

OUT

VIN = 12V

VIN = 24V

D1 = MBRM140
L1 = Toko D53LCB 33

300 400

LOAD CURRENT (mA)

µH

1933 G01

100

EFFICIENCY (%)

OUT

TA = 25°C

= 3.3V

V

OUT

90

80

70

60

0

VIN = 5V

VIN = 12V

100 200 600500

LOAD CURRENT (mA)

= 3.3V Switch Current Limit

1200

TA = 25°C

1000

800

VIN = 24V

D1 = MBRM140
L1 = Toko D53LCB 22

300 400

µH

1933 G02

600

400

SWITCH CURRENT LIMIT (mA)

200

0

20

0

Maximum Load Current Maximum Load Current Switch Voltage Drop

800

TA = 25°C

= 5V

V

OUT

700

600

LOAD CURRENT (mA)

500

L = 33µH

L = 22µH

800

TA = 25°C

= 3.3V

V

OUT

700

600

LOAD CURRENT (mA)

500

L = 22µH

L = 15µH

600

500

400

TA= 85°C

300

200

SWITCH VOLTAGE (mV)

100

TYPICAL

MINIMUM

40

DUTY CYCLE (%)

TA= 25°C

60

80

1933 G03

TA= –40°C

100

400

5

0

15

10

INPUT VOLTAGE (V)

20

3025

1933 G04

400

5

0

15

10

INPUT VOLTAGE (V)

20

3025

1933 G05

0

0

Feedback Voltage Undervoltage Lockout Switching Frequency

1.260

1.255

1.250

1.245

1.240

FEEDBACK VOLTAGE (V)

1.235

1.230
–50 –25 0 25 50 75 100 150125

TEMPERATURE (°C)

1933 G07

3.8

3.6

3.4

UVLO (V)

3.2

3.0
–50 –25 0 25 50 75 100 150125

TEMPERATURE (°C)

1933 G08

600

550

500

450

SWITCHING FREQUENCY (kHz)

400

–50 –25 0 25 50 75 100 150125

4

0.2 0.4

SWITCH CURRENT (A)

TEMPERATURE (°C)

0.60.1 0.3 0.5

1933 G06

1933 G09

1933fe

TYPICAL PERFORMANCE CHARACTERISTICS

Frequency Foldback Soft-Start SHDN Pin Current

700

600

500

TA = 25°C

1.4

1.2

1.0

TA = 25°C
DC = 30%

200

150

TA = 25°C

LT1933

400

300

200

SWITCHING FREQUENCY (kHz)

100

0

0.0

0.5

FB PIN VOLTAGE (V)

1.0 1.5

1933 G10

0.8

0.6

0.4

SWITCH CURRENT LIMIT (A)

0.2

0

0

1
SHDN PIN VOLTAGE (V)

234

1933 G11

100

50

SHDN PIN CURRENT (µA)

0

0

4
SHDN PIN VOLTAGE (V)

Typical Minimum Input Voltage Typical Minimum Input Voltage Switch Current Limit

8

7

TO START

6

INPUT VOLTAGE (V)

TO RUN

5

4

1 10 100

LOAD CURRENT (mA)

V

OUT

= 25°C

T

A

L = 33

= 5V

µH

1933 G13

6.0

5.5

TO START

5.0

4.5

4.0

INPUT VOLTAGE (V)

3.5

3.0

TO RUN

1 10 100

LOAD CURRENT (mA)

V

OUT

= 25°C

T

A

L = 22

= 3.3V

µH

1933 G14

1.4

1.2

1.0

0.8

0.6

0.4

SWITCH CURRENT LIMIT (A)

0.2

0

–25 0 25

–50

81216

1933 G12

50 75 100 150125

TEMPERATURE (°C)

1933 G15

VSW10V/DIV

I

200mA/DIV

L

V

10mV/DIV

OUT

Operating Waveforms

VIN = 12V, V
L = 22

µH, C

OUT
OUT

= 3.3V, I

= 22µF

OUT

= 400mA,

V

OUT1

1.8V

V

OUT2

1.2V

1933 G16

VSW10V/DIV

I

200mA/DIV

L

V

10mV/DIV

OUT

Operating Waveforms,
Discontinuous Mode

= 12V, V

V

IN

L = 22

µH, C

OUT
OUT

= 3.3V, I
= 22µF

OUT

= 20mA,

V

1.8V

V

OUT2

1.2V

1933 G17

OUT1

1933fe

5

LT1933

PIN FUNCTIONS

(SOT-23/DFN)

BOOST (Pin 1): The BOOST pin is used to provide a drive

voltage, higher than the input voltage, to the internal bipolar
NPN power switch.

GND (Pin 2/Pin 5 and Exposed Pad, Pin 7): Tie the
GND pin to a local ground plane below the LT1933 and
the circuit components. Return the feedback divider to
this pin.

FB (Pin 3/Pin 6): The LT1933 regulates its feedback pin to

1.245V. Connect the feedback resistor divider tap to this
pin. Set the output voltage according to V

= 1.245V

OUT

(1 + R1/R2). A good value for R2 is 10k.

BLOCK DIAGRAM

V

V

IN

IN

C2

INT REG

AND

UVLO

SHDN (Pin 4): The SHDN pin is used to put the LT1933 in
shutdown mode. Tie to ground to shut down the LT1933.
Tie to 2.3V or more for normal operation. If the shutdown
feature is not used, tie this pin to the V

pin. SHDN also

IN

provides a soft-start function; see the Applications Infor­mation section.

(Pin 5/Pin 2): The VIN pin supplies current to the

V

IN

LT1933’s internal regulator and to the internal power
switch. This pin must be locally bypassed.

SW (Pin 6): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.

ON OFF

R3

SHDN

C4

SLOPE
COMP

OSC

FREQUENCY
FOLDBACK

Σ

R

Q

S

V

GND

Q

C

g

m

1.245V

FB

R2 R1

DRIVER

BOOST

Q1

SW

D2

C3

L1

D1

1933 BD

V

OUT

C1

6

1933fe

LT1933

OPERATION

(Refer to Block Diagram)

The LT1933 is a constant frequency, current mode step
down regulator. A 500kHz oscillator enables an RS fl ip­fl op, turning on the internal 750mA power switch Q1. An
amplifi er and comparator monitor the current fl owing
between the V

and SW pins, turning the switch off when

IN

this current reaches a level determined by the voltage at

. An error amplifi er measures the output voltage through

V

C

an external resistor divider tied to the FB pin and servos

node. If the error amplifi er’s output increases, more

the V

C

current is delivered to the output; if it decreases, less cur­rent is delivered. An active clamp (not shown) on the V
node provides current limit. The V

node is also clamped

C

C

to the voltage on the SHDN pin; soft-start is implemented
by generating a voltage ramp at the SHDN pin using an
external resistor and capacitor.

APPLICATIONS INFORMATION

An internal regulator provides power to the control cir­cuitry. This regulator includes an undervoltage lockout
to prevent switching when V

is less than ~3.35V. The

IN

SHDN pin is used to place the LT1933 in shutdown, dis­connecting the output and reducing the input current to
less than 2µA.

The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate
the internal bipolar NPN power switch for effi cient opera­tion.

The oscillator reduces the LT1933’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during startup
and overload.

FB Resistor Network

The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis­tors according to:

R1 = R2(V

/1.245 – 1)

OUT

R2 should be 20k or less to avoid bias current errors.
Reference designators refer to the Block Diagram.

Input Voltage Range

The input voltage range for LT1933 applications depends
on the output voltage and on the absolute maximum rat­ings of the V

and BOOST pins.

IN

The minimum input voltage is determined by either the
LT1933’s minimum operating voltage of ~3.35V, or by its
maximum duty cycle. The duty cycle is the fraction of
time that the internal switch is on and is determined by
the input and output voltages:

DC = (V

where V
(~0.4V) and V

+ VD)/(VIN – VSW + VD)

OUT

is the forward voltage drop of the catch diode

D

is the voltage drop of the internal switch

SW

(~0.4V at maximum load). This leads to a minimum input
voltage of:

V

IN(MIN)

with DC

MAX

= (V

= 0.88

+ VD)/DC

OUT

MAX

– VD + V

SW

The maximum input voltage is determined by the absolute
maximum ratings of the V
minimum duty cycle DC

and BOOST pins and by the

IN

= 0.08 (corresponding to a

MIN

minimum on time of 130ns):

V

IN(MAX)

= (V

+ VD)/DC

OUT

– VD + V

MIN

SW

Note that this is a restriction on the operating input voltage;
the circuit will tolerate transient inputs up to the absolute
maximum ratings of the V

and BOOST pins.

IN

Inductor Selection and Maximum Output Current

A good fi rst choice for the inductor value is:

L = 5 (V

where V

+ VD)

OUT

is the voltage drop of the catch diode (~0.4V)

D

and L is in µH. With this value the maximum load current
will be above 500mA. The inductor’s RMS current rating
must be greater than your maximum load current and its

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