DEVICE DESCRIPTION
The ZXSC310 is a single or multi cell LED driver
designed for LCD backlighting applications. The input
voltage range of the device is between 0.8V and 8V.
This means the ZXSC310 is compatible with single
NiMH, NiCd or Alkaline cells, as well as multi-cell or
LiIon batteries.
The device features a shutdown control, resulting in a
standby current less than 5µA, and an output capable
of driving serial or parallel LED’s. The circuit generates
constant power output, which are ideal for driving
single or multiple LED’s over a wide range of operating
voltages. These features make the device ideal for
driving LED’s particularly in LCD backlight applications
for Digital Still cameras and PDA’s.
FEATURES
•94% efficiency
•Minimum operating input voltage 0.8V
•Maximum operating input voltage 8V
•Standby current less than 5µA
•Programmable output current
•Series or parallel LED configuration
•Low saturation voltage switching transistor
•SOT23-5 package
APPLICATIONS
•LCD backlights:
Digital still camera
PDA
Mobile phone
•LED flashlights and torches
•White LED driving
•Multiple LED driving
The ZXSC310 is a PFM DC-DC 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 conversion
enabling high efficiency conversion with low input
voltages. The drive output of the ZXSC310 LED driver
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 wider
range of load currents; several circuit configurations
are possible depending on battery life versus
brightness considerations.
The ZXSC310 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 LED backlight
applications.
ZXSC310
ISSUE 3 - SEPTEMBER 2007
1
SEMICONDUCTORS
LED DRIVER SOLUTION FOR LCD BACKLIGHTING
VIN
VCC
V
=3.3V/5V
DRIVE
ISENSE
Gnd
STDN
TYPICAL APPLICATIONS CIRCUIT
DEVICE REEL
SIZE
TAPE
WIDTH
QUANTITY
PER REEL
ZXSC310E5TA 180mm 8mm 3000
ORDERING INFORMATION
DEVICE MARKINGS
•C310
Package SOT23-5
ABSOLUTE MAXIMUM RATINGS:
Supply Voltage -0.3 to 10V
Maximum Voltage other pins -0.3 to VCC+0.3V
Power Dissipation 450mW
Operating Temperature -40 to 85 °C
Storage Temperature -55 to 150°C
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
2
Symbol Parameter Conditions Min Typ Max Units
Efficiency(1) 94 %
VCC Recommended supply
voltage range
0.8 8 V
VCC(min) Minimum startup and
operating voltage
IDRIVE=-600µA,VDRIVE=0.7V
IDRIVE=-600µA, VDRIVE=0.7V,
TAMB=-10°C(3)
0.8
0.9
0.92 V
IQQuiescent current(2) VEN = VCC (enabled)
VEN = 0V (standby)
0.2
510
mA
µA
IVDRIVE Base drive current VDRIVE =0.7V,V
ISENSE =0V 1.5 3.5 mA
ICC Supply current(3) VDRIVE =0.7V,V
ISENSE =0V 2 4 mA
VVDRIVE(high) High level drive voltage VISENSE =0V,I
VDRIVE =-0.5mA VCC
-0.3
VCC V
VVDRIVE(low) Low level drive voltage VISENSE = 50mV, IVDRIVE =5mA 0 0.2 V
VSTDN(high) Device enabled 0.7 V
VSTDN(low) Device in standby mode 0.15 V
ISTDN Enable input current -1 1 µA
VISENSE
(threshold)
Output current reference
voltage
14 19 24 mV
TCVISENSE ISENSE voltage temp co.(2) 0.4 %/°C
IISENSE ISENSE input current VISENSE =0V 0 -30 -65 µA
TDRV Discharge Pulse Width 1.2 1.7 3.2 µs
ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: VCC=1.5V, TAMB=25 C
Symbol Parameter Conditions Min Typ Max Units
FOSC Recommended operating
frequency(4) 200 kHz
OPERATING CONDITIONS
(1) Application dependent, see reference designs
(2) These parameters guaranteed by Design and characteristics
(3) Total supply current =IQ+I
VDRIVE, see typical characteristics
(4) Operating frequency is application circuit dependent. See applications section.
FMMT618
For the circuits described in the applications section
Zetex FMMT618 is the recommended pass transistor.
ZHCS1000
For the maximum brightness circuit described in the
applications section Zetex ZHCS1000 is the
recommended Schottky diode.
The following indicates outline data for the device,
more detailed information can be found at
www.zetex.com/fmmt618
The following indicates outline data for the ZHCS, more
detailed information can be found at
www.zetex.com/zhcs1000
ZXSC310
ISSUE 3 - SEPTEMBER 2007
SEMICONDUCTORS
3
Symbol Parameter Conditions Min Typ Max Units
VCE(sat) Collector-Emitter
Saturation Voltage5IC=0.1A, IB=10mA
IC=1A, IB=10mA
IC=2.5A, IB=50mA
8
70
130
15
150
200
mV
V(BR)CEO Collector-Emitter
Breakdown Voltage5IC=10mA 20 27 V
ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: TAMB=25 C
5Measured under pulse conditions. Pulse width=300µs. Duty cycle ⱕ2%
Symbol Parameter Conditions Min Typ Max Units
VFForward voltage IF= 500mA
IF=1A
400
500
mV
trr Reverse Recovery Time Switched from IF=500mA to
IR=500mA.
Measured at IR=50mA
12 ns
IRReverse Current VR= 30V 50 100 µA
ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: TAMB=25 C
Part
Number
VRIFIFSM VFat IRat Capacitance
at VR=25V,f=1MHz
Package
Max.
V
Max.
mA
Max.
A
Max.
mV
IF
mA
Max.
A
VR
V
Typ.
pF
SOT23
BAT54 30 200 0.6 500 30 250 25 10 SOT23-6
ZHCS2000 40 2000 20 500 2000 1000 30 60 SOT23
ZHCS1000 40 1000 12 500 1000 100 30 25 SOT23
ZHCS750 40 750 12 540 750 100 30 25 SOT23
ZHCS500 40 500 6.75 550 500 40 30 20 SOT23
ZHCS400 40 400 6.75 500 400 40 30 20 SOT323
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
4
TYPICAL CHARACTERISTICS
DEVICE DESCRIPTION
The ZXSC310 is PFM, controller IC which, when
combined with a high performance external transistor,
enables the production of a high efficiency boost
converter for LED driving applications. A block diagram
is shown for the ZXSC310 below.
The on chip comparator forces the driver circuit and
therefore the external switching transistor off if the
voltage at ISENSE exceeds 19mV. An internal reference
circuit and divider set this threshold.
The voltage at ISENSE is taken from a current sense
resistor connected in series with the emitter of the
switching transistor. A monostable following the
output of the comparator forces the turn-off time of the
output stage to be typically 1.7us. This ensures that
there is sufficient time to discharge the inductor coil
before the next on period.
With every on pulse the switching transistor is kept on
until the voltage across the current-sense resistor
exceeds the threshold of the ISENSE input. The on-pulse
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.
ZXSC310
ISSUE 3 - SEPTEMBER 2007
5
SEMICONDUCTORS
I
2
Drive
ISENSE
R2
VRE
R1
V
DRIVE
GND
I
VCC
STDN
ZXSC310 Block Diagram
REFERENCE DESIGNS
Three typical LED driving applications are shown.
Firstly a typical LCD backlight circuit, then maximum
brightness LED driving solution and lastly an optimised
battery life LED driving solution.
This application shows the ZXSC310 in a typical LCD
backlight application for Digital Still Cameras and
PDA’s. The input voltage for these backlight circuits are
usually fixed from the main system power, typically
3.3V or 5V. The LED’s are connected serially so that the
light is distributed uniformly in each LED. The current
provided to the LED’s can either be pulsed or DC. The
DC current is programmable via a sense resistor,
RSENSE, and is set to an optimum LED current of 20mA
for the reference designs. DC current is achieved by
adding a Schottky rectifying diode and an output
capacitor, as shown in the reference design below.
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
6
VIN
VCC
V
=3.3V/5V
DRIVE
ISENSE
Gnd
STDN
LCD backlight circuit
Ref Value Part Number Manufacture Comments
U1 N/A ZXSC310E5 Zetex Semiconductors Single cell converter, SOT23-5
Q1 N/A FMMT618 Zetex Semiconductors Low VCE(sat) NPN, SOT23
D1 N/A ZHCS1000 Zetex Semiconductors 1A Schottky diode, SOT23
C1 2.2F Generic Various 0805 Size
R1(6) 150m⍀Generic Various 1206 Size
R1(7) 250m⍀Generic Various 1206 Size
L1(8) 68µH Surface mount inductor
Materials list
(6) Used for 3.3V input, ILED set to 20mA ⫾10%.
(7) Used for 5V input, ILED to 20mA ⫾10%.
(8) See Application section.
(Notes)
ZXSC310
ISSUE 3 - SEPTEMBER 2007
7
SEMICONDUCTORS
This circuit provides a continuous current output to the
LED by rectifying and buffering the DC-DC output. This
ensures maximum LED brightness.
Ref Value Part Number Manufacturer Comments
U1 N/A ZXSC310E5 Zetex Plc Single cell converter, SOT23-5
Q1 N/A FMMT617 Zetex Plc Low VCE(sat) NPN, SOT23
D1 1A ZHCS1000 Zetex Plc 1A Shottky diode, SOT23
R1 100m⍀Generic Various 0805 Size
C1 2.2FGeneric Various Low ESR ceramic capacitor
L1 100µH(8) Surface mount inductor
Materials list
(8) See Application section.
Q1
FMMT617
R1
L1
V
D2
CC
G
I
V
S
U1
ZXSC310
D1
ZHCS1000
C1
BATT
V
DRIVE
TDN
SENSE
ND
Maximum brightness solution (Notes)
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.
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
8
Ref Value Part Number Manufacturer Comments
U1 N/A ZXSC310E5 Zetex Semiconductors Single cell converter, SOT23-5
Q1 N/A FMMT617 Zetex Semiconductors Low VCE(sat) NPN, SOT23
R1 330m⍀Generic Various 0805 Size
L1 100H(8) Surface mount inductor
Materials list
(8) See Application section.
Maximum battery life solution
(Notes)
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 transistor with low VCE(SAT) and high gain is
required.
The Zetex FMMT618 is an ideal choice of transistor,
having a low saturation voltage. A data sheet for the
FMMT618 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.
Schottky diode selection
For the maximum battery life solution a Schottky
rectifier diode is not 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
peak current in the inductor, and the maximum reverse
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
information is included in the characteristics section of
this data sheet.
For the maximum brightness solution a pulsed current
is supplied to the LED and thus a Schottky rectifier
diode is required.
Inductor selection
The inductor value must be chosen to satisfy
performance, cost and size requirements of the overall
solution. For the LCD backlight reference design we
recommend an inductor value of 68uH with a core
saturation current rating greater than the converter
peak current value and low series resistance.
Inductor selection has a significant impact on the
converter performance. For applications where
efficiency is critical, an inductor with a series resistance
of 500m⍀or less should be used.
A list of recommended inductors is shown in the table
below:
ZXSC310
ISSUE 3 - SEPTEMBER 2007
SEMICONDUCTORS
9
0.0
0.4
0. 1
0.2
0. 3
Part No. Manufacture L IPK RDC
DO1608C-683 Coilcraft 68H 0.4A 0.86⍀
CR54-680 Sumida 68H 0.61A 0.46⍀
P1174.683 Pulse 68H 0.4A 0.37⍀
SFOP5845-R61680 Samwha 68H 0.61A 0.46⍀
SIS43-680 Delta 68H 0.4 1.125⍀
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 190mA was chosen to ensure that the converter
could provide the required output power to the LED.
In general, the IPK value must be chosen to ensure that
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 IPK is decided the value of RSENSE can be
determined by:
A selection guide of sense resistor and inductor values
for given input voltages, output currents and number
of LED connected in series is provided in the table
below.
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
10
RV
I
SENSE
ISENSE
PK
=
Input Voltage
(V)
LED current
(mA)
No. of LED’s RSENSE
(m )
Inductor
(H)
Efficiency
(%)
3.3V 10 3 510 68 80
3.3V 10 4 330 68 81
3.3V 10 6 150 68 79
3.3V 20 3 220 68 84
3.3V 20 4 150 68 93
3.3V 20 6 77 68 79
3.3V 30 3 170 68 84
3.3V 30 4 100 68 84
3.3V 30 6 47 68 77
5V 10 3 750 68 83
5V 10 4 510 68 84
5V 10 6 330 68 79
5V 20 3 440 68 85
5V 20 4 250 68 85
5V 20 6 150 68 82
5V 30 3 330 68 86
5V 30 4 170 68 85
5V 30 6 100 68 83
Output Power Calculation
By making the above assumptions for inductance and
peak current the output power can be determined by:
Note:VOUT=output voltage + Schottky rectifier voltage
drop.
Where
TOFF ≅1.7us (internally set by ZXSC310)
and
and
Where
Operating frequency can be derived by:
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.
(notes)
ZXSC310
ISSUE 3 - SEPTEMBER 2007
11
SEMICONDUCTORS
()
IIVVT
L
MIN PK
OUT IN OFF
=− −×
()
FTT
ON OFF
=+
1
III
AV
PK MIN
=+
2
()
TTV V
V
ON
OFF OUT IN
IN
=−
PVVI T
TT
OUT OUT IN AV
OFF
ON OFF
=−××
+
()
Shutdown Control
The ZXSC310 offers a shutdown mode that produces a
standby current of less than 5uA when in operation.
When the voltage at the STDN pin is 0.7V or higher the
ZXSC310 is enabled, hence the driver is in normal
operation. When the voltage at the STDN pin is 0.1V or
lower the ZXSC310 is disabled, hence the driver is in
shutdown mode. If the STDN pin is open circuit the
ZXSC310 is also enabled.
Layout of LCD backlighting solution
Demonstration board
A demonstration board for the LCD backlighting
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.
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
12
Top Silk Drill File
Top Copper Bottom Copper
ZXSC310
ISSUE 3 - SEPTEMBER 2007
13
SEMICONDUCTORS
STDN
VCC
Gnd
ISENSE
VDRIVE
1
2
34
5
Top View
PINOUT DIAGRAM
Pin No. Name Description
1V
CC Supply voltage, generally Alkaline, NiMH or NiCd single cell
2G
nd Ground
3S
TDN Shutdown
4I
SENSE Inductor current sense input. Internal threshold voltage set to 19mV.
Connect external sense resistor
5V
DRIVE Drive output for external switching transistor. Connect to base of
external switching transistor.
PIN DESCRIPTIONS
(NOTES)
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
14
ZXSC310
ISSUE 3 - SEPTEMBER 2007
15
SEMICONDUCTORS
Definitions
Product change
Zetex Semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service.
Customers are solely responsible for obtaining the latest relevant information before placing orders.
Applications disclaimer
The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the user's
application and meets with the user's requirements. No representation or warranty is given and no liability whatsoever is assumed by Zetex with
respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or
otherwise. Zetex does not assume any legal responsibility or will not be held legally liable (whether in contract, tort (including negligence),
breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential loss in the use
of these circuit applications, under any circumstances.
Life support
Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express written
approval of the Chief Executive Officer of Zetex Semiconductors plc. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body
or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions
for use provided in the labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Reproduction
The product specifications contained in this publication are 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.
Terms and Conditions
All products are sold subjects to Zetex' terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two when the
terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement.
For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Zetex sales office.
Quality of product
Zetex is an ISO 9001 and TS16949 certified semiconductor manufacturer.
To ensure quality of service and products we strongly advise the purchase of parts directly from Zetex Semiconductors or one of our regionally
authorized distributors. For a complete listing of authorized distributors please visit: www.zetex.com/salesnetwork
Zetex Semiconductors does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales
channels.
ESD (Electrostatic discharge)
Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices. The
possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. The extent of damage
can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time. Devices suspected of
being affected should be replaced.
Green compliance
Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or exceeding regulatory
requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to reduce the use of
hazardous substances and/or emissions.
All Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance with WEEE and
ELV directives.
Product status key:
"Preview"Future device intended for production at some point. Samples may be available
"Active"Product status recommended for new designs
"Last time buy (LTB)"Device will be discontinued and last time buy period and delivery is in effect
"Not recommended for new designs"Device is still in production to support existing designs and production
"Obsolete"Production has been discontinued
Datasheet status key:
"Draft version"This term denotes a very early datasheet version and contains highly provisional
information, which may change in any manner without notice.
"Provisional version"This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance. However, changes to
the test conditions and specifications may occur, at any time and without notice.
"Issue"This term denotes an issued datasheet containing finalized specifications. However, changes to specifications may occur, at any time and
without notice.
SEMICONDUCTORS
ZXSC310
ISSUE 3 - SEPTEMBER 2007
16 SCZXSC310DS1
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D-81541 München
Germany
Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
europe.sales@zetex.com
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USA
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usa.sales@zetex.com
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Telephone: (852) 26100 611
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Telephone (44) 161 622 4444
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© Zetex Semiconductors plc 2007
DIM Millimeters 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° 0 10 0 10
SOT23-5 PACKAGE DIMENSIONSSOT23-5 PACKAGE OUTLINE
