Zetex Semiconductors PLC zxld1350ev2 User Manual

ZXLD1350EV2

ZXLD1350EV2 EVALUATION BOARD USER GUIDE

DESCRIPTION

The ZXLD1350EV2, Figure 1, is an evaluation board for evaluating the ZXLD13 50 350mA LED driver with internal switch. The evaluation board can be used to drive 1, 2 or 3 one- watt LEDs, or an external choice of LEDs. The number of external connected LEDs depends on the forward voltage of the LEDs connected. A connector, J1, is provided, which is compatible with the modular evalu ation system use d by Future Electro nics Ltd. The LEDs fitted on this evaluation board are from the LUXEON ® range distributed by Future Lighting Solutions (www.FutureLightingSolutions.com

The operating voltage is nominally 24V. For three 1W series-connected LE Ds, the voltage can be from 12V minimum to 30V maximum. The 100uH inductor used in the circuit is based on a nominal 24V supply, which should be connected across +VIN and GND pins. Note: The evaluation bo ard does not have reverse battery protection. The nominal current for the evaluation board is set at 300mA with a

Jumpers J1, J2 and J3 allow the selection of the number of LEDs to be connected in series. Jumper on at J1 bypasses LED D1. Jumper on at J3 bypasses LED D3. Removing jumper J2 disconnects all the on-board LEDs from the current flow path. Jumper 2 also doubles as a connection point for an ammeter to measure the LED current.

Before connecting external LEDs across test pins LED+ and LED-, or across J1, remove jumper J 2. Jumpers J1 and J2 can be on or off.

Test point ADJ provides a connection point for DC or PWM dimming and shutdown.

Warning: At 24V nominal operation with 300mA output, the LEDs and the PCB may be hot and the LEDs will be very bright.

)

0.33Ω sense resistor, Rs.

Figure 1: ZXLD1350EV2 evaluation board

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

ZXLD1350 DEVICE DESCRIPTION

The ZXLD1350 is a continuous mode inductive driver in a T SOT23-5 package, for driving one or more series connected LEDs efficiently from a voltage source higher t han the LED voltage. The device includes the output switch and a current sense circuit, which requires an external sens e resistor to set the nominal current up to 350mA.

ZXLD1350 DEVICE FEATURES

• Drives one or more series-connected 1W white LEDs up to 350mA.

• Internal 30V switch.

• Wide input voltage: 7V to 30V.

• Inherent open circuit LED protection.

• Brightness control using DC or PWM.

• Internal PWM filter.

DEVICE APPLICATIONS

• LED flashlights.

• High Power LED driving.

• Low-voltage halogen replacement LEDs.

• Automotive lighting.

• Illuminated signs.

ZXLD1350 Device Packages, Pin and Definitions

TSOT23-5 pack

ZXLD1350 Device Pin Definition Name Pin No Description

LX 1 Drain of NDMOS switch. GND 2 Ground (0V). ADJ 3 Internal voltage ref. pin (1.25V) :

• Leave floating for normal operation.

• Connect to GND to turn off output current.

• Drive with DC voltage (0.3V to 1.25V) or with PWM signal to adjust

output current or....

• Connect a capacitor from this pin to ground to set soft-start time.

ISENSE 4 Connect a sense resistor, Rs, from the ADJ pin to VIN to sense the nominal

output current. Nominal I

VIN 5 Input voltage: 7V to 30V. Decouple to ground with a 1uF or higher ceramic

capacitor.

= 0.1/ Rs

out

ORDERING INFORMATION

EVALBOARD ORDER NUMBER

ZXLD1350EV2

DEVICE ORDER NUMBER

ZXLD1350E5T A

Please note: Evaluation boards are subject to availability and qualified leads.

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

ZXLD1350EV2 EVALUATION BOARD REFERENCE DESIGN

The ZXLD1350EV2 is configured to the reference design in Figure 2. T he target application is a driver for one or more series-connected 1W white LEDs for torches and other high powered LED driving applications.

The operating voltage is a nominal 24V. For three 1W series-connected LEDs, the voltage can be from 12V minimum to 30V maximum. The nominal current is set at 300mA with a

connected 1–watt LEDs, with a nominal supply of 24V, the ZXLD1350 runs in continuous mode at 545kHz, with a

100uH inductor. Jumpers J1, J2 and J3 allow selection of the number of LEDs to be connected in series. Jumper on at J1 bypasses

LED D1. Jumper on at J3 bypasses LED D3. Removing jumper J2 disc onnects all the 1-watt LEDs from the current flow path. Jumper 2 also doubles as a connection point for an ammeter to measure the LED current.

Both DC and PWM dimming can be achieved by driving the ADJ pin. For DC dimming, the ADJ pin may be drive n between 0.3V and 1.25V. Driving the ADJ pin belo w 0.2V will shutdown the output current. For PWM dimming, an external open-collector NPN transistor or open-drain N-channel MOSFET can be used to drive the ADJ pin. The PWM frequency can be low, around 100Hz to 1kHz, or high between 10kHz to 50kHz. C3 should not evaluation board when using the PWM d imming feature. Shorting R 1 will connect t he test pin ADJ to device p in ADJ. The capacitor C3 should be around 10nF to decouple high frequency noise at the ADJ pin for DC dimming.

The soft-start time will be nominally 0.5ms without capacitor C3. Adding C3 will increase the soft start time by approximately 0.5ms/nF

For other reference designs or further applications information, please refer to the ZXLD1350 datasheet.

Schematic Diagram

Figure 2 shows the schematic for the ZXLD1350EV2 evaluation board.

0.33Ω sense resistor, Rs. For three series -

be fitted on the

Figure 2: Schematic for the evaluation board ZXLD1350EV2

ZXLD1350 Operation

In normal operation, when voltage is appli ed at +VIN, the ZXLD13350 internal NDMOS switch is turn ed on. Current starts to flow through sense resistor Rs, inductor L1, and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +VIN and the inductor L1. This rising current produces a voltage r amp across Rs. The internal circuit of the ZXLD1350 senses the voltage across Rs and applies a pro portional voltage to the input of the internal comparator. When this voltage reaches an internally set upper threshold, the NDMOS switch is turned off. The inductor current continues to flow through Rs, L1, the LEDs, the schottky diode SD1, and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop of the LEDs and the schottky diode. This decaying current produces a falling voltage at Rs, which is sensed by the ZXLD1350. A voltage proportional to the sense voltage across Rs is applied at the input of the internal c omparator. When this voltage falls to th e internally se t lower threshold, the NDMOS switch is turned on again. This switch-on-and- off cycle contin ues to provi de the aver age LED current set by the sense resistor Rs. Please refer to the datasheets for the threshold limits, ZXLD1350 internal circuits, electrical characteristics and parameters.

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

ZXLD1350EV2 Evaluation Board.

Ref Value Package Part Number Manufacturer Notes

RS 0.33R

1%,200ppm R1,R2 Not fitted 0805 Not fitted C1,C2 1uF, 50V 1206

C3 Not fitted 0805 Not fitted L1 100uH NPIS53D101MTRF NIC

SD1 40V, 1.16A SOT23 ZLLS1000 Zetex Schottky diode

U1 ZXLD1350 TSOT23-5 ZXLD1350E5TA Zetex DC-DC converter

D1, D2, D3 1W LED LXHL-PW01 Lumileds 1W power LED

JP1, JP2,

JP3

+VIN, GND,

ADJ, LED a,

LED k

J1 6 way

The slugs of the 1-watt LEDs are connected to isolated copper 'floods' both on the top and bottom layers, with thermal inter-connection between the layers. The slugs a re electrically isolated from other circuits and pads on the evaluation board. Warning: At a nominal 24V operation with 300mA output, th e board temperature rises by

around 30C from ambient after 30 minutes of operation.

Jumper Various 2.54mm pitch

Test loop 100-108 Hughes

connector

0805 NCST10FR330FTRF NIC

components

50V, 1206 X7R

NMC1206X7R105K50F

5535676-5 TYCO

NIC

components

100uH/0.5A rms

components

jumper pin strips

Inductor

Z X LD1350EV2 EVALUATION B OA RD

JP 2

In partnershi p with:

+VI N

GND

ADJ

JP 1

JP 3

SD1

LED k

LED a

Bar e boar d: ZDB308R3 Copyr ight Z etex Plc 2006

ZXLD1350EV2 User Guide Iss 5 10-04-07

Figure 3: Component layout

ZXLD1350EV2

ZXLD1350EV2 EVALUATION BOARD

LED k

LED a

+VIN

GND

ADJ

JP1

JP3

JP2

SD1

In par tner ship with:

Bare boar d: Z DB 308R3 Copyright Z et ex P lc 2006

Figure 4: Top View Figure 5: Bottom View

ZXLD1350EV2 Connection Point Definition Name Description

+VIN Positive supply voltage. Connect a +24V positive supply to this pin. GND

Supply Ground (0V). Connect supply ground to this pin.

ADJ Internal voltage ref. pin (1.25). This pin can be used to achieve dimming and soft-start,

and for switching the output current off.

• Leave floating for normal operation.

• See 'Other Features' section to achieve dimming, and soft-start and for switching

the output current off.

LED a LED a connects to the ANODE of LED D3, and is the external LED anode connection

point. Disconnect the jumper JP2 when driving an external load.

LED k LED k connects to the CATHODE of LED D1, and is the external LED cathode

connection point. Disconnect the jumper JP2 when driving external LEDs.

J1 Pins 1 & 2: LED a, Pins 5 & 6: LED k

ZXDL1350EV2 OPERATION ZXLD1350EV2 Power Up

1. Connect VIN to +24V of the power supply unit (PSU). Connect GND to the power supply ground (0V).

Warning: The board does not feature reverse battery/supply protection.

2. Set the PSU to +24V. (+24V at VIN pin with ref. to the GND pin.)

3. Turn on the PSU.

Warning: Do not stare at the LEDs directly.

4. Ensure jumper J2 is fitted. With JP1 and JP3 disconnected (jumper off), all three LEDs should illuminate and will be regulated nominally at 300mA.

5. To change the number of LEDs connected in series, use jumper JP1 and JP3 to bypass LEDs D1 and D3 respectively.

Warning: The LEDs may be hot.

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

OTHER FEATURES

Dimming The ZXLD1350 provides three dimming options: DC, high-frequency PWM, and low-frequency PWM dimming.

DC Voltage Dimming

1. Switch off the power supply.

2. Solder a link across R1 pads.

3. Fit a 10nF capacitor at C3 to decouple the pin.

4. Drive the ADJ pin on the board with a DC voltage in the range 0.3V to 1.25V.

5. Do not exceed 1.25V, as this represents 100% of the LED current set b y Rs. The current will increase in proportion to this voltage. For example, if 2.5V is applied, the current will increase to 200%. That is, the current will be twice the 1.25V rating. For such over-drive of the ADJ pin, the LED and ZXLD1350 are likely to be damaged. The nominal LED current (output current), I

= 0.08* V

OUT

/Rs where I

ADJ

= the nominal LED current.

OUT

= the DC dimming voltage at ADJ pin resistor.

ADJ

0.08 is the multiplier for the reference voltage on ADJ pin. Rs = the sense resistor value in ohms.

Do not use a resistor value lower than 0.27Ω.

6. The dimming ratio is around 6:1. Note: as the voltage approaches 0.2V on the ADJ pin, the ZXLD1350 will shut down.

7. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

High Frequency PWM Dimming

1. Switch off the power supply.

2. Solder a link across R1 pads.

3. Ensure C3 is not fitted.

4. Connect a PWM signal to the ADJ pin via an open collector NPN transistor, or an open drain N-c hannel MOSFET.

5. Alternatively, drive the ADJ pin directly with a PWM signal. However, make sure the PWM signal voltage levels do not violate the ADJ pin voltage rating. Drivin g the ADJ pin above 1.25V will e xceed the maximum set current for the value of Rs and may damage the device or LED.

6. Set the PWM frequency to between 10KHz and 50KHz. The cut-off frequency of the internal filter is 4kHz, and exceeding the 50kHz may cause modulation with the switching regulator.

7. The dimming ratio will be about 6:1, similar to the DC dimming. The nominal LED current (output cur rent), I

is given by

OUT,

= 0.1*D/Rs where I

OUT

= the nominal LED current.

OUT

Rs = the sense resistor value in ohms.

Do not use a resistor value lower than 0.27Ω.

D = the duty cycle of the PWM dimming frequency.

0.1V is the nominal sense voltage with ADJ open circuit or set to 1.25V.

Note: The ADJ pin is internally referenced to 1.25V. This pin should be left floating for normal operation without dimming. Please refer to the datasheet for PWM frequency.

8. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

, is given by

OUT

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

Low Frequency PWM Dimming

1. Switch off the power supply.

2. Solder a link across R1 pads.

3. Make sure C3 is not fitted.

4. Connect a PWM signal to the ADJ pin via an open co llector NPN transistor or an open drain N-channel MOSFET.

6. The PWM frequency can be low; around 100Hz or up to 1kHz.

7. The Z XLD1350 is now effectively bein g turned on and off at the PWM frequency. T he dimming ratios are in the region of 100:1, much greater than the DC dimming ratio. The aver age l LED current (output current), I

is given by

OUT,

= 0.1*D/Rs where I

OUT

D = the duty cycle of the PWM dimming frequency.

8. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

Soft-start

1. Switch off the power supply.

2. Solder a link across R1 pads.

3. Fit a capacitor at C3 to decouple the pin. The value of C3 will determine the so ft-start time setting. Please see the datasheet for calculation of the capacitor value.

4. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

Switching the output current off

1. Switch off the power supply.

2. Solder a link across R1 pads.

3. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

4. Connect the ADJ pin to GND to turn off the output current.

5. Follow the ‘ZXLD1350EV2 Power Up’ sequence. The ZXLD1350 internal switch remains switched off (output current off) whilst the ADJ pin is pulled to GND.

Changing the LED current

1. Switch off the power supply.

2. Remove Rs.

3. Calculate and fit a ne w sense resistor, Rs, the value of which is based on the required LED current without dimming. Rs can be calculated using following equation :

Rs = 0.1V/I

4. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

Using external LEDs or loads

1. Switch off the power supply.

2. Connect external LEDs across test pins ‘LED a’ and ‘LED k’. ‘LED a ’ is the LEDs' anode connection point and ‘LED k’ is the LEDs' cathode connection point. The number of external LEDs that can be connect ed depends on their operating power and forward voltage drop. For an external load other than LEDs, the positive terminal of the load should be connected to test pin ‘LED a’ and the negative terminal of the l oad should be connected to test pin ‘LED k’. Connector J1 is compatible with the ‘Luxeon® Emitter Board System’ from Future Electronics, or can be used to connect LEDs via pin-strip connectors.

3. Follow the ‘ZXLD1350EV2 Power Up’ sequence.

where I

OUT

= the average LED current.

OUT

Rs = the sense resistor value in ohms.

Do not use a resistor value lower than 0.27Ω.

0.1V is the nominal sense voltage with ADJ open circuit or set to 1.25V.

= the LED current.

OUT

Rs = the sense resistor value in ohms.

Do not use a resistor value lower than 0.27Ω.

0.1V is the nominal sense voltage with ADJ open circuit or set to 1.25V.

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

PERFORMANCE

The system efficiency depends on the sense resistor, supply voltage, switching in ductor and the number of 1W LEDs connected in series.

The graph below shows the efficiency with a 0.33Ω sense resistor R connected 1W LEDs.

With a 24V supply, the switching frequency is typically 545kHz for three series-co nnected 1-watt LEDs and 300kHz for a single 1-watt LED.

With a 12V supply, the switching frequency is typically 160kHz for three series-co nnected 1-watt LEDs and 280kHz for a single 1-watt LED

The detailed performance information for the device can be found in the datasheets.

Efficiency vs Vin

Rsense=0.33 Ohms, L=100uH (NIC NPIS53D101MTRF)

and a 100uH inductor, for 1 to 3 series

Eff (%)

0 5 10 15 20 25 30 35

Vin (V)

Figure 6: Efficiency vs supply voltage

1 LED 2 LED 3 LED

ZXLD1350EV2 User Guide Iss 5 10-04-07

ZXLD1350EV2

Definitions

Product change

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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:

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

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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.

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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 “Provisional version” This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance. However, “Issue” This term denotes an issued datasheet containing finalized specifications. However, changes to specifications

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1. are intended to implant into the body

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.

failure of the life support device or to affect its safety or effectiveness.

information, which may change in any manner without notice. changes to the test conditions and specifications may occur, at any time and without notice. may occur, at any time and without notice.

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ZXLD1350EV2 User Guide Iss 5 10-04-07

Zetex Semiconductors PLC zxld1350ev2 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

DESCRIPTION

ORDERING INFORMATION