Datasheet ZXSC300E5 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.
Theseapplicationsmainlyoperatefromsingle1.5Vor

1.2V battery cells. The circuit generates constant
current pulses that are ideal for driving single or
multiple LED’s over a wide range of operating
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

FEATURES

• 94% efficiency

• Minimum operating input voltage 0.8V

• Fixed output current

• Low saturation voltage switching transistor

•

SOT23-5 package

the switching transistor.
The circuit can start up under full load and operates

down to an input voltage of 0.8 volts. The solution
configurationensuresoptimumefficiencyovera wide
range of load currents, several circuit configurations
are possible depending on battery life versus
brightness considerations.

The ZXSC300 is offered in the SOT23-5 package
which, when combined with a SOT23 switching
transistor, generates a high efficiency small size
circuit solution. The IC and discrete combination
offers the ultimate cost vs performance solution for
single cell LED driving applications.

ZXSC300

TYPICAL APPLICATION CIRCUIT

V

BATT

L1

100µH

U1

V

cc

V

drive

I

sense

Gnd

ZXSC300

ISSUE 1 - JUNE 2001

Q1

FMMT617

R1

0.33R

LED1

WHITE LED

ORDERING INFORMATION

DEVICE Package Partmarking

ZXSC300E5 SOT23-5 C300

1

ZXSC300

ABSOLUTE MAXIMUM RATING

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

ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: V

CC

+0.3V

Operating Temperature -40 to 85°C
Storage Temperature -55 to 125°C

=1.5V, T

CC

AMB

=25°C

Symbol Parameter Conditions Min Typ Max Units

η

V

CC

Efficiency

Recommended
supply voltage

1

0.8 8 V

94 %

range

V

CC(min)

I

Q

I

VDRIVE

I

CC

V

VDRIVE(high)

V

VDRIVE(low)

V

ISENSE

(threshold)

T

CVISENSE

I

ISENSE

ELECTRICAL CHARACTERISTICS: AC PARAMETERS

Minimum startup
and operating
voltage

Quiescent current

2

Base drive current V

Supply current

3

High level drive
voltage

Low level drive
voltage

Output current
reference voltage

I

SENSE

voltage temp co.

I

input current V

SENSE

2

I

DRIVE

I

DRIVE

T

AMB

DRIVE

V

DRIVE

V

ISENSE

V

ISENSE

ISENSE

=-600µA, V

=-600µA, V

3

=-10°C

DRIVE

DRIVE

=0.7V

=0.7V,

0.8

0.9

0.92 V

0.2 mA

= 0.7V, V

= 0.7V, V

= 0V, I

= 50mV, I

VDRIVE

= 0V 1.5 3.6 mA

ISENSE

=0V 2 4 mA

ISENSE

=-0.5mA VCC-0.3 V

= 5mA 0 0.2 V

VDRIVE

CC

14 19 24 mV

0.4 %/°C

= 0V 0 -30 -65 µA

2

TEST CONDITIONS (Unless otherwise stated) )
V

=1.5V, T

CC

= 0 to 70°C

AMB

V

Symbol Parameter Conditions Min Typ Max Units

T

DRV

F

OSC

1

Application dependent, see reference designs.

2

These parameters guaranteed by Design

3

Total supply current =IQ+ I

4

Operating frequency is application circuit dependent. See applications section.

Discharge Pulse Width 1.2 1.7 3.2 µs
Recommended operating

frequency

4

, see typical characteristics

VDRIVE

200 kHz

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ZXSC300

FMMT617

For the circuits described in the applications section, ZetexFMMT617 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

V

CE(sat)

8

70

150

Collector-Emitter
Breakdown Voltage

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

V

(BR)CEO

15 18 V IC=10mA*

14
100
200

mV
mV
mV

I

=0.1A, IB=10mA*

C

I

=1A, IB=10mA*

C

I

=3A, IB=40mA*

C

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

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
500mVmV

50 100

µA

IF=500mA
I

VR=30V

12 ns Switched from IF= 500mA

to I
at I

=1A

F

= 500mA. Measured

R

=50mA

R

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3

3

ZXSC300

TYPICAL CHARACTERISTICS

300µ

200µ

100µ

Quiescent Current (A)

0

12345678

Input Voltage (V)

Quiescent Current v Input Voltage

30m

25m

20m

15m

10m

5m

Sense Voltage (V)

0

12345678

Input Voltage (V)

Sense Voltage v Input Voltage

4m

3m

2m

1m

Drive Current (A)

0

12345678

Input Voltage (V)

Drive Current v I nput Voltage

100

95

90

Efficiency (%)

85

1.0 1.5 2.0 2.5 3.0 3.5

Input Voltage (V)

Input Voltage v Efficiency

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ZXSC300

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

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 thecomparatorforces theturn-offtime ofthe
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

With every on pulse the switching transistor is kept on
until the voltage across the current-sense resistor
exceedsthe threshold oftheI
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.

input.The on-pulse

SENSE

Pin out Diagram

CC

ND

1

2

3

Top View

V

DRIVE

5

I

SENSE

4

V

G

Pin No. Name Description

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

5V

ISSUE 1 - JUNE 2001

CC

SENSE

DRIVE

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

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

C1

100mΩ

2.2µF

Generic Various 0805 Size

Generic Various Low ESR ceramic capacitor

L1 100µH DO1608P-104 Coilcraft Surface mount inductor

LED1 5600mcd NSPW500BS Nichia White LED

CE(sat)

NPN, SOT23

ISSUE 1 - JUNE 2001

6

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

L1

330mΩ
100µH

Generic Various 0805 Size

DO1608P-104 Coilcraft Surface mount inductor

LED1 5600mcd NSPW500BS Nichia White LED

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CE(SAT)

NPN, SOT23

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,a bipolar transistorwithlow V
high gain is required.

CE(SAT)

and

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, andthe maximumreverse
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
informationis included inthecharacteristics section of
this data sheet.

Forthemaximum brightness solution a pulsedcurrent
is supplied to the LED therefore a Schottky rectifier
diode is not required.

Inductor selection

The inductor value must be chosen to satisfy
performance,costand size requirements of theoverall
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.

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

value must be chosen to ensure that

PK

maximum output power conditions, assuming
worse-case input voltage and transistor gain under all
operating temperature extremes.

Once I
determined by:

R

SENSE

where V

is decided the value of R

PK

V

ISENSE

=

I

PK

=19mV

ISENSE

SENSE

can be

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ZXSC300

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

=

OUT

Note: V
drop

OUT- IN PK MIN

= output voltage + Schottkyrectifier voltage

OUT

2

+)( )

T

x

()+

TT

ON OFF

OFF

where
T

≅ 1.7µs (internally set by ZXSC300)

OFF

and

TV V

T

=

ON

−()

OFF OUT IN

V

IN

and

II

=−

MIN PK

(V - V xT

OUT IN OFF

)

L

Operating frequency can be derived by:

F

1

=

TT

+

()

ON OFF

Layout of Maximum battery life solution

Capacitor selection

For pulsed operation, as in themaximum 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 Maximum battery 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.

Top Copper

Drill Holes

Bottom Copper Silk Screen

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ZXSC300

(Notes)

10

ISSUE 1 - JUNE 2001

Supplier Listing

Zetex

AVX

Coilcraft

Nichia Corporation

ZXSC300

GERMANY ASIA USA UK

Zetex GmbH
Munich

(49) 894549490 (852) 2610 0611 (1) 631 543 7100 (44) 161 622 4444
http://www.zetex.com

http://www.avxcorp.com

http://www.coilcraft.com
Nichia Europe B.V.

Amsterdam
The Netherlands
(31) 20 5060900

http://www.nichia.co.jp

Zetex Asia
Hong Kong

AVX Asia
Singapore
(65) 258 2833

Nichia Corporation
Tokyo Sales Office
Tokyo, Japan
(81) 3 3456 3784

Zetex Inc
Long Island NY

AVX USA
(1) 843 448 9411

Coilcraft Inc
(1) 847 639 6400

Nichia America
Corporation
Head Office
(1) 717 285 2323
San Jose
(1) 408 573 0933

Zetex PLC
Chadderton,
Oldham

AVX UK
(44) 1252 770000

Coilcraft Europe
(44) 1236 730595

ISSUE 1 - JUNE 2001

11

ZXSC300

ZXSC300

PACKAGE DIMENSIONS SOT23-5

DIM

Millimetres Inches
MIN MAX MIN MAX

A 0.90 1.45 0.035 0.057
A1 0.00 0.15 0.00 0.006
A2 0.90 1.3 0.035 0.051
b 0.35 0.50 0.014 0.020
C 0.09 0.20 0.0035 0.008
D 2.80 3.00 0.110 0.118
E 2.60 3.00 0.102 0.118
E1 1.50 1.75 0.059 0.069
e 0.95 REF 0.037 REF
e1 1.90 REF 0.075 REF
L 0.10 0.60 0.004 0.024
a° 010010

Zetex plc.
Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom.
Telephone: [phone] (Sales), (44)161 622 4444 (General Enquiries)
Fax: [phone]

Zetex GmbH Zetex Inc. Zetex (Asia) Ltd. These are supported by
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D-81673 München Commack NY 11725 Hing Fong Road, major countries world-wide
Germany USA Kwai Fong, Hong Kong © Zetex plc 2001
Telefon: [phone] Telephone: [phone] Telephone:[phone]
Fax: [phone] Fax: [phone] Fax: [phone] www.zetex.com

This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or
reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services
concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or
service.

Publication Ref. SCZXSC300DS

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