ZETEX ZXSC310 LED Driver Solution For LCD Backlighting Owner’s Manual

ZETEX ZXSC310 LED Driver Solution For LCD Backlighting

Product Information

The ZXSC310 is an LED driver solution designed for LCD backlighting applications. It is a PFM DC-DC controller IC that drives an external Zetex switching transistor with low saturation resistance, enabling high-efficiency conversion with low input voltages. The device can start up under full load and operate down to an input voltage of 0.8 volts. The ZXSC310 offers a compact circuit solution with high efficiency.

Specifications:

• Device: ZXSC310
• Input Voltage Range: 0.8V – 8V
• Package: SOT23-5
• Operating Frequency: 200kHz

Features:

• Compatible with single or multi-cell batteries
• High efficiency with low input voltages
• SOT23-5 package for small-size circuit solution

Typical Applications Circuit:
Insert Typical Applications Circuit Image Here

Ordering Information:

• Device: ZXSC310E5TA
• Reel Size: 180mm
• Tape Quantity: 3000

Product Usage Instructions

1. Circuit Configuration:
   The ZXSC310 can be configured in various ways depending on battery life versus brightness considerations. Refer to the application circuit section for detailed configurations.

2. Power Supply:
   Ensure the input voltage supplied to the ZXSC310 is within the range of 0.8V to 8V for optimal performance.

3. Connection:
   Connect the ZXSC310 to the LED backlight according to the typical application circuit provided in the manual.

FAQ:

• Q: What is the recommended operating frequency for ZXSC310?
  A: The recommended operating frequency for ZXSC310 is 200kHz, but it may vary based on the application circuit.

• Q: What is the pass transistor recommended for use with ZXSC310?
  A: For the circuits described in the applications section, Zetex FMMT618 is the recommended pass transistor.

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 LEDs. 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 LEDs, particularly in LCD backlight applications for Digital Still cameras and PDAs.
• 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 operate 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.

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

ORDERING INFORMATION

DEVICE MARKINGS

• C310
  Package SOT23-5

TYPICAL APPLICATIONS CIRCUIT

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

ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: VCC=1.5V, TAMB=25 C

Symbol| Parameter| Conditions| Min| Typ| Max| Units
---|---|---|---|---|---|---
 | Efficiency 1|  |  |  | 94| %
VCC| Recommended supply voltage range|  | 0.8|  | 8| V
VCC( m in)| Minimum startup and operating voltage| IDRIVE=-600µ A, VDRIVE=0.7V

IDRIVE=-600µ A, VDRIVE=0.7V, TA M B=-10°C3

|  | 0.8

0.9

| 0.92| V
IQ| Quiescent current 2| VEN = VCC (enabled)

VEN = 0V (standby)

|  | 0.2

5

| ****

10

| m A

µ A

IVDRIVE| Base drive current| V DRIVE = 0.7V, VISENSE = 0V| 1.5|  | 3.5| m A
ICC| Supply current 3| VDRIVE = 0.7V, VISENSE = 0V| 2|  | 4| mA
 |  |  |  |  |  |
VVDRIVE( high)| High-level drive voltage| V ISENSE = 0V, IVDRIVE =-0.5 m A| VCC

-0.3

|  | VCC| V
VVDRIVE( low )| Lo w level drive voltage| V ISENSE = 50 m V, IVDRIVE = 5 m A| 0|  | 0.2| V
VSTDN( high)| Device enabled|  | 0.7|  |  | V
VSTDN( lo w )| Device in standby m ode|  |  |  | 0.15| V
ISTDN| Enable input current|  | -1|  | 1| µA
VISENSE

( threshold)

| Output current reference voltage|  | 14| 19| 24| m V
TCVISENSE| ISENSE voltage tem p co. 2|  |  | 0.4|  | %/°C
IISENSE| ISENSE input current| V ISENSE = 0V| 0| -30| -65| µ A
TDRV| Discharge Pulse Width|  | 1.2| 1.7| 3.2| µs

OPERATING CONDITIONS

Sy m bol| Parameter| Conditions| Min| Typ| Max| Units
---|---|---|---|---|---|---
FOSC| Recommended operating frequency 4|  |  |  | 200| kHz

1. Application dependent, see reference designs
2. These parameters are guaranteed by Design and characteristics
3. Total supply current =IQ + IVDRIVE, see typical characteristics
4. Operating frequency is application circuit dependent. See the applications section.

FMMT618

• For the circuits described in the applications section ZetexFMMT618is the recommended pass transistor.
• The following indicates outline data for the device, more detailed information can be found in the Zetex surface mount products data book or on the Zetex Web page: www.zetex.com.

ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: TAMB=25 C.

Symbol| Parameter| Conditions| Min| Typ| Max| Units
---|---|---|---|---|---|---
VCE(sat)| Collector-Emitter

Saturation Voltage 5

| IC=0.1A, IB=10 m A

IC=1A, IB=10 m A

|  | 8

70

| 15

150

| m V
 |  | IC=2.5A, IB=50 m A| 130| 200|
V(BR)CEO| Collector-Emitter

Breakdown Voltage 5

| IC=10 m A| 20| 27|  | V

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

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 ZHCS, more detailed information can be found on the Zetex Web page: www.zetex.com.

ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: TAMB=25 °C

Symbol| Parameter| Conditions| Min| Typ| Max| Units
---|---|---|---|---|---|---
VF| Forward voltage| I F = 500 m A

IF = 1A

|  |  | 400

500

| m V
t rr| Reverse Recovery Time| Sw itched from I F=500 m A to IR=500 m A.

Measured at IR=50 m A

|  | 12|  | ns
IR| Reverse Current| V R = 30V|  | 50| 100| µ A
Part Nu m ber| VR

Max. V

| IF

Max. m A

| IFS M

Max. A

| VF at| IR at| Capacitance

at VR = 25V, f = 1 MHz

Typ.

pF

| Package

SOT23

---|---|---|---|---|---|---|---
Max.

m V

| IF

m A

| Max.

µA

| VR V
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

TYPICAL CHARACTERISTICS

DEVICE DESCRIPTION

• The ZXSC310 is a 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 period.
• With every 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 the applications section for details.
• The driver circuit supplies the external switching transistor with a fixed drive current. To maximize efficiency the external transistor switched quickly, typically being forced off within 30ns.

REFERENCE DESIGNS
Three typical LED driving applications are shown. Firstly a typical LCD backlight circuit, then a maximum brightness LED driving solution, and lastly an optimized battery life LED driving solution.

LCD backlight circuit

This application shows the ZXSC310 in a typical LCD backlight application for Digital Still Cameras and PDAs. The input voltage for these backlight circuits are usually fixed from the main system power, typically 3.3V or 5V. The LEDs are connected serially so that the light is distributed uniformly in each LED. The current provided to the LEDs can either be pulsed or DC. The DC is programmable via a sense resistor, RSENSE, and is set to an optimum LED current of 20mA for the reference designs. DC is achieved by adding a Schottky rectifying diode and an output capacitor, as shown in the reference design below.

Materials list

• 6. Used for 3.3V input, ILED set to 20mA ±10%.
• 7. Used for 5V input, ILED to 20mA ±10%.
• 8. See the Application section.

Maximum brightness solution

This circuit provides a continuous current output to the LED by rectifying and buffering the DC-DC output. This ensures maximum LED brightness.

Materials list

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.

Materials list

Ref| Value| Part

Number

| Manufacturer| Comments
---|---|---|---|---
U1| N/A| ZXSC310E5| Zetex Plc| Single-cell converter, SOT23-5
Q1| N/A| FMMT617| Zetex Plc| Lo w V CE(SAT) NPN, SOT23
R1| 330 mf1| Generic| Various| 0805 Size
L1| 100µH8|  |  | Surface mount inductor

APPLICATIONS INFORMATION

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

Switching transistor selection

• The choice of switching transistors 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 the Zetex website 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 the Zetex website 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 the 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’s performance. For applications where efficiency is critical, an inductor with a series resistance of 500mΩ or less should be used.
• A list of recommended inductors is shown in the table below:

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 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: RSENSE= VISENSE/IPK
• 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.

Input Voltage

(V)

| LED current

(mA)

| No. of LED’s| R SENSE

(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.

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.

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.

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

Layout of LCD backlighting solution

Top Silk

PINOUT DIAGRAM

PIN DESCRIPTIONS

m V. Connect external sense resistor
5| V DRIVE| Drive output for external switching transistor. Connect to the base of the external switching transistor.

SOT23-5 PACKAGE OUTLINE

SOT23-5 PACKAGE DIMENSIONS

Contact Information

Europe

• Zetex GmbH Streitfeldstraße 19 D-81673 München Germany
• Telefon: (49) 89 45 49 49 0
• Fax: (49) 89 45 49 49 49
• europe.sales@zetex.com

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• Zetex Inc
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• Telephone: (1) 631 360 2222

• Fax: (1) 631 360 8222

• usa.sales@zetex.com

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• Zetex (Asia) Ltd
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• Telephone: (852) 26100 611

• Fax: (852) 24250 494

• asia.sales@zetex.com

Corporate Headquaters

• Zetex plc
  Fields New Road, Chadderton Oldham, OL9 8NP United Kingdom

• Telephone (44) 161 622 4444

• Fax: (44) 161 622 4446

• hq@zetex.com

These offices are supported by agents and distributors in major countries worldwide. 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. For the latest product information, log on to www.zetex.com.

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