Allegro STR-X6757 INSTALLATION INSTRUCTIONS

STR-X6757

Off-Line Quasi-Resonant Switching Regulators

Features and Benefits

▪ Quasi-resonant topology IC  Low EMI noise and soft

switching

▪ Bottom-skip mode  Improved system efficiency over

the entire output load by avoiding increase of switching
frequency

▪ Auto-Standby mode  Lowers input power at very light

output load condition

▪ Avalanche-guaranteed MOSFET  Improves system-level

reliability and does not require V

▪ 650 V
▪ Various protections  Improved system-level reliability

▫ Pulse-by-pulse drain overcurrent limiting
▫ Overvoltage Protection (bias winding voltage sensing),

with latch

▫ Overload Protection with latch
▫ Maximum on-time limit

/ 0.62 Ω R

DSS

DS(on)

derating

DSS

Package: 7-Pin TO-3P

Description

The STR-X6757 is a quasi-resonant topology IC designed for
SMPS applications. It shows lower EMI noise characteristics
than conventional PWM solutions, especially at greater than
2 MHz. It also provides a soft-switching mode to turn on the
internal MOSFET at close to zero voltage (VDS bottom point)
by use of the resonant characteristic of primary inductance
and a resonant capacitor.

The package is a fully molded TO-3P, which contains the
controller chip (MIC) and MOSFET, enabling output power
up to 320 W at 230 VAC and 165 W at universal input. The
bottom-skip mode skips the first bottom of VDS and turns on the
MOSFET at the second bottom point, to minimize an increase
of operating frequency at light output load, improving system­level efficiency over the entire load range.

There are two standby modes available to reduce the input power
under very light load conditions. The first is Auto-Standby
mode, which is internally triggered by periodic sensing, and
the other is a manual standby mode, which is executed by
clamping the secondary output. In general applications, the
manual standby mode reduces the input power further compared
to Auto-Standby mode.

Not to scale

Continued on the next page…

T ypical Application

28103.30-10

STR-X6757

Off-Line Quasi-Resonant Switching Regulators

Description (continued)

The soft-start mode minimizes surge voltage and reduces power stress
to the MOSFET and to the secondary rectifying diodes during the
start-up sequence. Various protections such as overvoltage, overload,
overcurrent, maximum on-time protections and avalanche-energy­guaranteed MOSFET secure good system-level reliability.

Applications include the following:

▪ Set Top Box
▪ LCD PC monitor, LCD TV
▪ Printer, Scanner
▪ SMPS power supplies

Selection Guide

Part Number Package

STR-X6757 TO-3P

Absolute Maximum Ratings at T

= 25°C

A

Parameter Symbol Conditions Rating Unit

Drain Current
Maximum Switching Current
Single Pulse Avalanche Energy
Input Voltage for Controller (MIC) V
SS/OLP Terminal Voltage V
FB Terminal Inflow Current I
FB Terminal Voltage V
OCP/BD Terminal Voltage V

MOSFET Power Dissipation

Controller (MIC) Power Dissipation P
Operating Internal Leadframe Temperature T
Operating Ambient Temperature T
Storage Temperature T
Channel Temperature T

1

Refer to MOSFET ASO curve

2

I

DMAX

3

Refer to Avalanche Energy Derating curve

4

Refer to MOSFET Ta-PD1 curve

1

2

3

4

IDpeak Single pulse 18 A

I

DmaxTA

E

AS

CC

SSOLP

FB

FBIFB

OCPBD

P

D1

D2

OP

stg

ch

= –20°C to 125°C 18 A

Single pulse, V

within the limits of I

= 30 V, L = 50 mH, I

DD

FB

Lpeak

With infinite heatsink 44 W
Without heatsink 2.8 W
V

× I

CC

CC

Recommended operation temperature, see cautions –20 to 125 °C

F

is the drain current determined by the drive voltage of the IC and the threshold voltage, Vth, of the MOSFET

All performance characteristics given are typical values for circuit or
system baseline design only and are at the nominal operating voltage and
an ambient temperature, T

, of 25°C, unless oth er wise stated.

A

= 3.53 A 326 mJ

35 V

–0.5 to 6.0 V

10 mA
–0.5 to 9.0 V
–1.5 to 5.0 V

0.8 W

–20 to 125 °C
–40 to 125 °C

150 °C

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

2

STR-X6757

Functional
Block Diagram

Off-Line Quasi-Resonant Switching Regulators

Terminal List Table

Number Name Description Functions

1 D Drain MOSFET drain

2 S Source MOSFET source

3 GND Ground terminal Ground

4 VCC Power supply terminal Input of power supply for control circuit

5 SS/OLP Soft Start/Overload Protection terminal Input to set delay for Overload Protection and Soft Start operation

6 FB Feedback terminal

7 OCP/BD Overcurrent Protection/Bottom Detection Input for Overcurrent Detection and Bottom Detection signals

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Input for Constant Voltage Control and Burst (intermittent) Mode
oscillation control signals

3

STR-X6757

0

20

40

60

80

100

0 20 40 60 80 100 120

A.S.O. temperature derating coefficient (%)

TF [℃]

Internal frame temperature

STR-X6757

A.S.O. tem perature derating coefficient

curve

0

20

40

60

80

100

25 50 75 100 125 150

E

AS

temperature derating coefficient (%)

Tch [℃]

Channel temperature

STR-X6757

Avalanch e energy d erating cu rve

0.01

0.1

1

10

100

1 10 100 1000

I

D

[A]

Drain Current

VDS[V]

Drain-to-Source Voltage

STR-X6757

MOSFET A.S.O. Curve

Determined by On-Resistance

1ms

100μs

Off-Line Quasi-Resonant Switching Regulators

App ly A.S.O temp erature
co efficient fr om the l eft graph to
th is cur ve fo r ev aluating actual
op erations' safety

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

4

STR-X6757

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140

P

D1

[W]

Power dissipation

Ta[℃]

Ambient temperature

STR-X6757

MOSFET Ta-P

D1

Curve

PD1=2.8[W]

With infinite heatsink

Without heatsink

PD1=44[W]

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100 120 140

P

D2

〔Ｗ〕

Power dissipation

TF〔℃〕

Internal frame temperature

STR-X6757

MIC T

F-PD2

Curve

0.001

0.01

0.1

1

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01

θch-c[℃/W]

Transient thermal resistance

t [sec]

time

STR-X6757

Transient thermal resistance curve

Off-Line Quasi-Resonant Switching Regulators

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

5

STR-X6757

Off-Line Quasi-Resonant Switching Regulators

ELECTRICAL CHARACTERISTICS

Characteristic Symbol Test Conditions Min. Typ. Max. Units

ELECTRICAL CHARACTERISTICS for Controller (MIC)

1

, valid at TA = 25°C, VCC = 20 V, unless otherwise specified

Power Supply Start-up Operation

osc

VCC = 0→20 V

VCC = 20→8.8 V

VCC = 15 V

V

increasing

SS/OLP

V

= 0 V

SS/OLP

16.3 18.2 19.9 V

8.8 9.7 10.6 V

––6mA

– – 100 μA

19 22 25 kHz

1.1 1.2 1.4 V

–710 –550 –390 μA

Operation Start Voltage V

Operation Stop Voltage V

Circuit Current In Operation I

Circuit Current In Non-Operation I

Oscillation Frequency f

Soft Start Operation Stop Voltage V

Soft Start Operation Charging Current I

SSOLP(SS)

SSOLP(SS)

CC(ON)

CC(OFF)

CC(ON)

CC(OFF)

Normal Operation

Bottom-Skip Operation Threshold Voltage 1 V

Bottom-Skip Operation Threshold Voltage 2 V

Overcurrent Detection Threshold Voltage V

OCP/BD Terminal Outflow Current I

Quasi-Resonant Operation Threshold Voltage 1 V

Quasi-Resonant Operation Threshold Voltage 2 V

FB Terminal Threshold Voltage V

FB Terminal Inflow Current (Normal Operation) I

OCPBD(BS1)

OCPBD(BS2)

OCPBD(LIM)

OCPBD

OCPBD(TH1)

OCPBD(TH2)

FB(OFF)

FB(ON)

V

falling

OCP/BD

V

= –0.95 V

OCP/BD

V

falling

OCP/BD

V

rising

OCP/BD

VFB rising

VFB = 1.6 V

–0.720 –0.665 –0.605 V

–0.485 –0.435 –0.385 V

–0.995 –0.940 –0.895 V

–250 –100 –40 μA

0.28 0.40 0.52 V

0.67 0.80 0.93 V

1.32 1.45 1.58 V

600 1000 1400 μA

Standby Operation

Standby Operation Start Voltage V

Standby Operation Start Voltage Interval V

Standby Non-Operation Circuit Current I

FB Terminal Inflow Current, Standby Operation I

FB Terminal Threshold Voltage, Standby Operation V

Minimum On Time t

CC(S)

CC(SK)

CC(S)

FB(S)

FB(S)

ON(MIN)

VCC = 0→15 V, VFB = 1.6 V

V

= V

CC(SK)

CC(S)

– V

CC(OFF)

VCC = 10.2 V, VFB = 1.6 V

VCC = 10.2 V, VFB = 1.6 V

VCC = 15 V, VFB rising

10.3 11.2 12.1 V

1.10 1.35 1.65 V

–2056μA

–414μA

0.55 1.10 1.50 V

0.65 1.00 1.35 μs

Protection Operation

Maximum On Time t

Overload Protection Operation Threshold Voltage V

Overload Protection Operation Charging Current I

Overvoltage Protection Operation Voltage V

Latch Circuit Holding Current

Latch Circuit Release Voltage

2

2

ELECTRICAL CHARACTERISTICS for MOSFET, valid at T

Drain-to-Source Breakdown Voltage V

Drain Leakage Current I

On Resistance R

Switching Time t

Thermal Resistance R

1

Current polarity with respect to the IC: positive current indicates current sink at the terminal named, negative current indicates source at the

terminal named.

2

The latch circuit means a circuit operated OVP and OLP.

ON(MAX)

SSOLP(OLP)

V

= 2.5 V

SSOLP(OLP)

CC(OVP)

I

CC(H)

V

CC(La.OFF)

DSS

DSS

DS(on)IDS

θch-F

SS/OLP

VCC = 0→30 V

V

– 0.3 V

CC(OFF)

VCC = 30→6 V, OVP operating

= 25°C, unless otherwise specified

A

I

= 300 μA 650 – – V

DSS

V

= 650 V – – 300 μA

DSSS

= 3.4 A – – 0.62 Ω

f

Channel to internal frame – – 1.09 °C/W

27.5 32.5 39.0 μs

4.0 4.9 5.8 V

–16 –11 –6 μA

25.5 27.7 29.9 V

– 45 140 μA

6.0 7.2 8.5 V

– – 500 ns

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

6

STR-X6757

100 pieces per tray
5 trays per inner carton
(Outer packing dependent on quantity)

Dimensions in millimeters

48

333

Off-Line Quasi-Resonant Switching Regulators

Packing Specifications

388

137

364

177

4 inner cartons per outer carton
500 pieces maximum per inner carton
2000 pieces maximum per outer carton

137

Dimensions in millimeters

356

206

2 inner cartons per outer carton
500 pieces maximum per inner carton
1000 pieces maximum per outer carton

Dimensions in millimeters

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

7

STR-X6757

Off-Line Quasi-Resonant Switching Regulators

Package Outline Drawing, TO-3P

15.6 ±0.2

Gate Burr

Branding
Area

View A

2X 2.54±0.1 4X 1.27±0.1

Terminal dimension at lead tip

6

XXXXXXXX

XXXXXXXX

XXXXXXXX

257

1

2 ±0.2

5.5±0.2

634

23 ±0.3

5.5±0.2

6.7±0.5

12.5±0.5

5.8

REF

4.3 ±0.5

Terminal dimension at lead tip

0.55

3.45±0.2

Ø3.2 ±0.2

3.35±0.1

+0.2
–0.1

3.6 ±0.5

3.3

1.33

2X 0.83

+0.2
–0.1

+0.2
–0.1

1.89

+0.2
–0.1

3

5X 0.75

5X 0.65

+0.2
–0.1

+0.2
–0.1

Gate burr: 0.3 mm (max.)
Terminal core material: Cu
Terminal treatment: Ni plating and Pb-free solder dip
Leadform: 1905

Approximate weight: 6 g

Dimensions in millimeters

Leadframe plating Pb-free. Device composition
includes high-temperature solder (Pb >85%),
which is exempted from the RoHS directive.

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

0.5

Front View (Plan View)

0.5

Drawing for reference only
Branding codes (exact appearance at manufacturer discretion):
1st line, type: STR
2nd line, subtype: X6757
3rd line, lot: YM DD
Where: Y is the last digit of the year of manufacture
M is the month (1 to 9, O, N, D)
DD is the 2-digit date

Enlargement View A

8

STR-X6757

WARNING — These devices are designed to be operated at lethal voltages and energy levels. Circuit

designs that embody these components must conform with applicable safety requirements. Pre cau­ tions must be taken to prevent accidental contact with power-line potentials.

The use of an isolation transformer is recommended during circuit development and breadboarding.

Off-Line Quasi-Resonant Switching Regulators

Because reliability can be affected adversely by improper storage
environments and handling methods, please observe the following
cautions.

Cautions for Storage

• Ensure that storage conditions comply with the standard
temperature (5°C to 35°C) and the standard relative humidity
(around 40 to 75%); avoid storage locations that experience
extreme changes in temperature or humidity.

• Avoid locations where dust or harmful gases are present and
avoid direct sunlight.

• Reinspect for rust on leads and solderability of products that have
been stored for a long time.

Cautions for Testing and Handling

When tests are carried out during inspection testing and other

standard test periods, protect the products from power surges
from the testing device, shorts between adjacent products, and
shorts to the heatsink.

Remarks About Using Silicone Grease with a Heatsink

• When silicone grease is used in mounting this product on a

heatsink, it shall be applied evenly and thinly. If more silicone
grease than required is applied, it may produce stress.

• Coat the back surface of the product and both surfaces of the

insulating plate to improve heat transfer between the product and
the heatsink.

• Volatile-type silicone greases may permeate the product and

produce cracks after long periods of time, resulting in reduced
heat radiation effect, and possibly shortening the lifetime of the
product.

• Our recommended silicone greases for heat radiation purposes,

which will not cause any adverse effect on the product life, are
indicated below:

Type Suppliers

G746 Shin-Etsu Chemical Co., Ltd.

YG6260 Momentive Performance Materials

SC102 Dow Corning Toray Silicone Co., Ltd.

Heatsink Mounting Method

• Torque When Tightening Mounting Screws. Thermal resistance

increases when tightening torque is low, and radiation effects are
decreased. When the torque is too high, the screw can strip, the heatsink
can be deformed, and distortion can arise in the product frame. To avoid
these problems, observe the recommended tightening torques for this
product package type, TO-3P: 0.588 to 0.785 N•m (6 to 8 kgf•cm).

• For effective heat transfer, the contact area between the product and
the heatsink should be free from burrs and metal fragments, and the
heatsink should be flat and large enough to contact over the entire
side of the product, including mounting flange and exposed thermal
pad, and have a minimal mounting hole to prevent possible deflection
and cracking of the product case when fastened to the heatsink.

Soldering

• When soldering the products, please be sure to minimize the
working time, within the following limits:

260±5°C 10 s

350±5°C 3 s

• Soldering iron should be at a distance of at least 1.5 mm from the

body of the products

Electrostatic Discharge

• When handling the products, operator must be grounded.
Grounded wrist straps worn should have at least 1 MΩ of
resistance to ground to prevent shock hazard.

• Workbenches where the products are handled should be
grounded and be provided with conductive table and floor mats.

• When using measuring equipment such as a curve tracer, the
equipment should be grounded.

• When soldering the products, the head of soldering irons or the
solder bath must be grounded in other to prevent leak voltages
generated by them from being applied to the products.

• The products should always be stored and transported in our
shipping containers or conductive containers, or be wrapped in
aluminum foil.

Recommended operation temperature

• Inner frame temperature in operation T

= 115°C

F

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

9

STR-X6757

Off-Line Quasi-Resonant Switching Regulators

The products described herein are manufactured in Ja pan by Sanken Electric Co., Ltd. for sale by Allegro MicroSystems, Inc.

Sanken and Allegro reserve the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be re quired to per mit im­ prove ments in the per for mance, reliability, or manufacturability of its prod ucts. Therefore, the user is cau tioned to verify that the in for ma tion in this
publication is current before placing any order.

When using the products described herein, the ap pli ca bil i ty and suit abil i ty of such products for the intended purpose shall be reviewed at the users
responsibility.

Although Sanken undertakes to enhance the quality and reliability of its prod ucts, the occurrence of failure and defect of semi con duc tor products
at a certain rate is in ev i ta ble.

Users of Sanken products are requested to take, at their own risk, preventative measures including safety design of the equipment or systems
against any possible injury, death, fires or damages to society due to device failure or malfunction.

Sanken products listed in this publication are designed and intended for use as components in general-purpose electronic equip ment or apparatus
(home ap pli anc es, office equipment, tele com mu ni ca tion equipment, measuring equipment, etc.). Their use in any application requiring radiation
hardness assurance (e.g., aero space equipment) is not supported.

When considering the use of Sanken products in ap pli ca tions where higher reliability is re quired (transportation equipment and its control systems
or equip ment, fire- or burglar-alarm systems, various safety devices, etc.), contact a company sales representative to discuss and obtain written
confirmation of your spec i fi ca tions.

The use of Sanken products without the written consent of Sanken in applications where ex treme ly high reliability is required (aerospace equip­ment, nuclear power-control stations, life-support systems, etc.) is strictly prohibited.

The information in clud ed herein is believed to be accurate and reliable. Ap pli ca tion and operation examples described in this pub li ca tion are
given for reference only and Sanken and Allegro assume no re spon si bil i ty for any in fringe ment of in dus tri al property rights, intellectual property
rights, or any other rights of Sanken or Allegro or any third party that may result from its use. The contents in this document must not be transcribed
or copied without Sanken’s or Allegro's written consent.

Copyright ©2009 Allegro MicroSystems, Inc.

This datasheet is based on Sanken datasheet SSE-23855

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

10

STR-X6757

Off-Line Quasi-Resonant Switching Regulators

Worldwide Contacts

Asia-Pacific
China

Sanken Electric Hong Kong Co., Ltd.

Suite 1026, Ocean Centre, Canton Road

Tsimshatsui, Kowloon, Hong Kong

Tel: [phone], Fax: [phone]

Sanken Electric (Shanghai) Co., Ltd.

Room 3202, Maxdo Centre, Xingyi Road 8

Changning District, Shanghai, China

Tel: [phone], Fax: [phone]

Taiwan Sanken Electric Co., Ltd.

Room 1801, 18th Floor, 88 Jung Shiau East Road

Sec. 2, Taipei 100, Taiwan R.O.C.

Tel: [phone], Fax: [phone]

Japan

Sanken Electric Co., Ltd.

Overseas Sales Headquarters

Metropolitan Plaza Building, 1-11-1 Nishi-Ikebukuro

Toshima-ku, Tokyo 171-0021, Japan

Tel: [phone], Fax: [phone]

Korea

Sanken Electric Korea Co., Ltd.

Mirae Asset Life Building, 6F

168 Kongduk-dong, Mapo-ku

Seoul 121-705, Korea

Tel: [phone], Fax: [phone]

Singapore

Sanken Electric Singapore Pte. Ltd.

150 Beach Road, #14-03 The Gateway West

Singapore 189720

Tel: [phone], Fax: [phone]

Europe

Sanken Power Systems (UK) Limited

Pencoed Technology Park

Pencoed, Bridgend CF35 5HY, United Kingdom

Tel: [phone], Fax: [phone]

North America

United States

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01606, U.S.A.

Tel: [phone], Fax: [phone]

Allegro MicroSystems, Inc.

14 Hughes Street, Suite B105

Irvine, California 92618, U.S.A.

Tel: [phone], Fax: [phone]

Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

11