Datasheet ZXSC300 Datasheet (ZETEX)

SINGLE OR MULTI CELL LED DRIVER SOLUTION

DESCRIPTION

The ZXSC300 is a single or multi cell LED driver
designed for applications where step-up voltage
conversion from very low input voltages is required.
These applicationsmainly operate from single 1.5V or

1.2V battery cells. The circuit generates constant
current pulses that are ideal for driving single or
multipleLED’soverawide rangeofoperating voltages.

The ZXSC300 is a PFM controller IC that drives an
external Zetex switching transistor with a very low
saturation resistance. These transistors are the best
switching devices available for this type of switching
conversion enabling high efficiency conversion with
input voltages below 1 volt. The drive output of the
ZXSC controller generates a dynamic drive signal for
the switching transistor.

The circuit can start up under full load and operates
down to an input voltage of 0.8 volts. The solution
configuration ensures optimum efficiency over a wide
range of load currents, several circuit configurations
are possible depending on battery life versus
brightness considerations.

TheZXSC300isofferedintheSOT23-5packagewhich,
when combined with a SOT23 switching transistor,
generates a high efficiency small size circuit solution.
The IC and discrete combination offers the ultimate
costvsperformance solution forsinglecell LED driving
applications.

ZXSC300

FEATURES

94% efficiency

•

• Minimum operating input voltage 0.8V

•

Fixed output current

•

Low saturation voltage switching transistor

•

SOT23-5 package

TYPICAL APPLICATION CIRCUIT

V

BATT

L1

100µH

U1

V

cc

V

drive

I

sense

Gnd

ZXSC300

Q1

FMMT617

R1

0.33R

LED1

WHITE LED

APPLICATIONS

LED flashlights and torches

•

• LED backlights

•

White LED driving

•

Multiple LED driving

•

Solar Equipment

ORDERING INFORMATION

DEVICE Reel Tapewidth Quantity

ZXSC300E5TA 7” 8mm 3,000

per reel

DEVICE MARKING C300

Package SOT23-5

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1

SEMICONDUCTORS

ZXSC300

ABSOLUTE MAXIMUM RATING

Supply Voltage -0.3 to 10V
Maximum Voltage Other Pins -0.3 to V
Power Dissipation 450mW

CC

+0.3V

Operating Temperature -40 to 85°C
Storage Temperature -55 to 150°C

ELECTRICAL CHARACTERISTICS: Test conditions unless otherwise stated: V

=1.5V, T

CC

AMB

=25°C

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNITS

η

V

CC

V

CC(min)

I

Q

I

VDRIVE

I

CC

V

VDRIVE(high)

V

VDRIVE(low)

V

ISENSE

(threshold)
T

CVISENSE

I

ISENSE

T

DRV

Efficiency
Recommended

1

0.8 8 V

supply voltage range

Minimum startup
and operating
voltage

Quiescent current
Base drive current V
Supply current

3

High level drive
voltage

Low level drive
voltage

Output current

I

=-600µA, V

DRIVE

=-600µA, V

I

DRIVE

T

AMB

2

DRIVE

V

DRIVE

V

ISENSE

V

ISENSE

=-10°C

= 0.7V, V
= 0.7V, V

=0V,I

= 50mV, I

3

=0.7V

DRIVE

=0.7V,

DRIVE

= 0V 1.5 3.6 mA

ISENSE

=0V 2 4 mA

ISENSE

=-0.5mA VCC-0.3 VCCV

VDRIVE

= 5mA 0 0.2 V

VDRIVE

14 19 24 mV

reference voltage

I

SENSE

voltage temp co.
I

input current V

SENSE

2

= 0V 0 -30 -65 µA

ISENSE

Discharge pulse width 1.2 1.7 3.2 µ s

94 %

0.8

0.92 V

0.9

0.2 mA

0.4 %/°C

OPERATING CONDITIONS

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNITS

F

OSC

1

Application dependent, see reference designs.

2

These parameters guaranteed by design and characterisation

3

Total supply current =IQ+ I

4

Operating frequency is application circuit dependent. See applications section.

SEMICONDUCTORS

Recommended operating frequency

, see typical characteristics

VDRIVE

4

200 kHz

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2

ZXSC300

FMMT617

For the circuits described in the applications section, Zetex FMMT617 is the recommended pass transistor. The
following indicates outline data for the transistor, more detailed information can be found in the Zetex surface
mount data book or at www.zetex.com

ELECTRICAL CHARACTERISTICS (at TA= 25°C unless otherwise stated).

PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS

Collector-Emitter
Saturation Voltage

Collector-Emitter
Breakdown Voltage

V

CE(sat)

V

(BR)CEO

15 18 V IC=10mA*

8

70

150

*Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤ 2%

ZHCS1000

For the circuits described in the applications section Zetex ZHCS1000 is the recommended Schottky diode. The
following indicates outline data for the diode, more detailed information is available at www.zetex.com

14
100
200

mV
mV
mV

IC=0.1A, IB=10mA*
I

=1A, IB=10mA*

C

I

=3A, IB=40mA*

C

ELECTRICAL CHARACTERISTICS (at T

PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS

Forward Voltage V

Reverse Current I
Reverse Recovery

Time

F

R

t

rr

= 25°C unless otherwise stated).

amb

400

500
50 100
12 ns Switched from IF= 500mA

mV
mV

µA

IF=500mA
I

=1A

F

VR=30V

to I

= 500mA. Measured at

R

I

=50mA

R

*Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤ 2%

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SEMICONDUCTORS

ZXSC300

TYPICAL CHARACTERISTICS

SEMICONDUCTORS

ISSUE 2 - FEBRUARY 2004

4

DEVICE DESCRIPTION

The ZXSC300 is PFM, controller IC which, when
combined with a high performance external
transistor, enables the production of a high efficiency
boost converter for use in single cell LED driving
applications. A block diagram is shown for the
ZXSC300 in Figure 1.

Figure 1 ZXSC300 Block Diagram

ZXSC300

With every on pulse the switching transistor iskepton
until the voltage across the current-sense resistor
exceedsthethreshold of theI
length, and therefore the switching frequency, is
determined by the programmed peak current, the
input voltage and the input to output voltage
differential. See applications section for details.

The Driver circuit supplies the external switching
transistor with a fixed drive current. To maximise
efficiency the external transistor switched quickly,
typically being forced off within 30ns.

Pin out Diagram

input.Theon-pulse

SENSE

The on chip comparator forces the driver circuit and
therefore the external switching transistor off if the
voltage at I
by an internal reference circuit and divider.

The Voltage at I
resistor connected in series with the emitter of the
switching transistor. A monostable following the
outputof the comparatorforcesthe turn-offtimeof the
output stage to be typically 1.7µs. This ensures that
there is sufficient time to discharge the inductor coil
before the next on period.

exceeds 19mV. This threshold is set

SENSE

is taken from a current sense

SENSE

Pin Descriptions

Pin No. Name Description

1V
2 Gnd Ground
3 N/C Not connected
4I

5V

CC

SENSE

DRIVE

ISSUE 2 - FEBRUARY 2004

Supply voltage, generally Alkaline, NiMH or NiCd single cell

Inductor current sense input. Internal threshold voltage set to 19mV.
Connect external sense resistor

Drive output for external switching transistor. Connect to base of external
switching transistor

5

SEMICONDUCTORS

ZXSC300

REFERENCE DESIGNS

Two typical LED driving applications are shown.
Firstly a maximum brightness solution and
secondly an optimised battery life solution.

Maximum brightness solution

This circuit provides a constant current output to
the LED by rectifying the switching pulses. This
ensures maximum LED brightness.

VBATT

L1

100µH

U1

V

cc

V

drive

I

sense

Gnd

ZXSC300

Q1

FMMT617

R1

0.1R

D1

ZHCS1000

C1

2.2µF

LED1

WHITE LED

Material List

Ref Value Part Number Manufacture Comments

U1 N/A ZXSC300E5 Zetex Plc Single cell converter, SOT23-5
Q1 N/A FMMT617 Zetex Plc Low V
D1 1A ZHCS1000 Zetex Plc 1A Shottky diode, SOT23
R1 100mW Generic Various 0805 Size
C1 2.2mF Generic Various Low ESR ceramic capacitor
L1 100µH DO1608P-104 Coilcraft Surface mount inductor
LED1 5600mcd NSPW500BS Nichia White LED

CE(sat)

NPN, SOT23

SEMICONDUCTORS

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Maximum battery life solution

To ensure optimum efficiency, and therefore
maximum battery life, the LED is supplied with a
pulsed current. Maximum efficiency is ensured with
the removal of rectifier losses experienced in the

maximum brightness solution.

V

BATT

L1

100µH

U1

V

cc

V

drive

I

sense

Gnd

ZXSC300

Q1

FMMT617

R1

0.33R

LED1

WHITE LED

100

Single LED Load

95

90

Efficiency (%)

85

1.0 1.5 2.0 2.5 3.0 3.5

InputVoltage v Efficiency

ZXSC300

Input Voltage (V)

Materials list

Ref Value Part Number Manufacture Comments

U1 N/A ZXSC300E5 Zetex Plc Single cell converter, SOT23-5
Q1 N/A FMMT617 Zetex Plc Low V
R1 330mW Generic Various 0805 Size
L1 100mH DO1608P-104 Coilcraft Surface mount inductor
LED1 5600mcd NSPW500BS Nichia White LED

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CE(SAT)

NPN, SOT23

SEMICONDUCTORS

ZXSC300

APPLICATIONS INFORMATION

The following section is a design guide for optimum
converter performance.

Switching transistor selection

The choice of switching transistor has a major impact
on the converter efficiency. For optimum
performance,abipolar transistor withlowV
high gain is required.

Schottky diode selection

For the maximum battery life solution a Schottky
rectifier diode is required. As with the switching
transistor the Schottky rectifier diode has a major
impact on the converter efficiency. A Schottky diode
with a low forward voltage and fast recovery time
should be used for this application.

The diode should be selected so that the maximum
forward current is greater or equal to the maximum
peakcurrent intheinductor, and themaximumreverse
voltage is greater or equal to the output voltage.

The Zetex ZHCS1000 meets these needs. Datasheets
for the ZHCS Series are available on Zetex web site or
through your local Zetex sales office. Outline
informationisincluded in thecharacteristicssectionof
this data sheet.

Forthemaximumbrightness solution a pulsed current
is supplied to the LED therefore a Schottky rectifier
diode is not required.

Inductor selection

The inductor value must be chosen to satisfy
performance,costandsize requirements of the overall
solution. For the reference designs we recommend an
inductor value of 100uH with a core saturation current
rating greater than the converter peak current value
and low series resistance.

CE(SAT)

and

The Zetex FMMT617 is an ideal choice of transistor,
having a low saturation voltage. A data sheet for the
FMMT617 is available on Zetex web site or through
your local Zetex sales office. Outline information is
included in the characteristics section of this data
sheet.

Inductor selection has a significant impact on the
converter performance. For applications where
efficiency is critical, an inductor with a series
resistance of 500mΩ or less should be used.

Peak current definition

The peak current rating is a design parameter whose
value is dependent upon the overall application. For
the high brightness reference designs, a peak current
of was chosen to ensure that the converter could
provide the required output power to the LED.

In general, the I
the switching transistor, Q1, is in full saturation with
maximum output power conditions, assuming
worse-case input voltage and transistor gain under all
operating temperature extremes.

Once I

PK

determined by:

SENSE

=

ISENSE

V

R

where V

value must be chosen to ensure that

PK

is decided the value of R

ISENSE

I

PK

=19mV

SENSE

can be

SEMICONDUCTORS

ISSUE 2 - FEBRUARY 2004

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Output Power Calculation

By making the above assumptions for inductance and
peak current the output power can be determined by:

(V V x I I

P

Note: V
drop

OUT- IN PK MIN

=

OUT

OUT

= output voltage + Schottky rectifier voltage

where
T

≅ 1.7µs (internally set by ZXSC300)

OFF

and

TV V

OFF OUT IN

T

=

ON

V

and

II

MIN PK

(V - V xT

=−

+)( )

2

x

−()

IN

OUT IN OFF

)

L

T

OFF

()+

TT

ON OFF

ZXSC300

Operating frequency can be derived by:

F

Capacitor selection

For pulsed operation, as in the maximum battery life
solution, no capacitors are required at the output to
the LED. For rectified operation, as in the maximum
brightness solution, a small value ceramic capacitor
is required, typically 2.2uF.

Generally an input capacitor is not required, but a
small ceramic capacitor may be added to aid EMC,
typically 470nF to 1uF.

Demonstration board

A demonstration board for the Maximumbattery life
solution, is available upon request. These can be
obtained through your local Zetex office or through
Zetex web pages. For all reference designs Gerber
files and bill of materials can be supplied.

1

=

TT

+

()

ON OFF

Layout of Maximum battery life solution

Top Copper

Drill Holes

Bottom Copper Silk Screen

ISSUE 2 - FEBRUARY 2004

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SEMICONDUCTORS

ZXSC300

Notes:

SEMICONDUCTORS

ISSUE 2 - FEBRUARY 2004

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SUPPLIER LISTING

Manufacturer EUROPE ASIA USA

Zetex

Tel: [phone] (852) 2610 0611 (1) 631 543 7100

URL: http://www.zetex.com

AVX

Tel: [phone] (65) 6286 7555 (1) 843 448 9411

URL: http://www.avxcorp.com

Coilcraft

Tel: [phone] (1) 847 639 6400

URL: http://www.coilcraft.com

Nichia Corporation

Tel: [phone] (81) 3 3456 3784 Head Office

URL: http://www.nichia.co.jp

Zetex GmbH
Germany

AVX UK AVX Asia

Coilcraft Europe
UK

Nichia Europe B.V.
The Netherlands

Zetex Asia
Hong Kong

Singapore

Nichia Corporation
Japan

ZXSC300

Zetex Inc

AVX USA

Coilcraft Inc

Nichia America
Corporation

(1) 717 285 2323
San Jose
(1) 408 573 0933

ISSUE 2 - FEBRUARY 2004

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SEMICONDUCTORS

ZXSC300

PACKAGE DIMENSIONSPACKAGE OUTLINE

Millimeters Inches

DIM

MIN. MAX. MIN. MAX.

A 0.90 1.45 0.0354 0.0570
A1 - 0.15 - 0.0059
A2 0.90 1.30 0.0354 0.0511
b 0.20 0.50 0.0078 0.0196
C 0.09 0.26 0.0035 0.0102
D 2.70 3.10 0.1062 0.1220
E 2.20 3.20 0.0866 0.1181
E1 1.30 1.80 0.0511 0.0708
e 0.95 REF 0.0374 REF
e1 1.90 REF 0.0748 REF
L 0.10 0.60 0.0039 0.0236
a 0° 30° 0° 30°

© Zetex plc 2003

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ISSUE 2 - FEBRUARY 2004

SEMICONDUCTORS

12