Zetex Semiconductors PLC ZXLD1362EV3 User Manual

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ZXLD1362EV3 USER GUIDE

DESCRIPTION

The ZXLD1362EV3, Figure 1, is a PCB constructed using an aluminium base for evaluating the ZXLD1362 LED driver with internal switch [1]. The evaluation board can be used to drive an external choice of LEDs; the total forward voltage across the LEDs depending on the number and type connected.

The operating voltage is nominally higher than 30V for the external LEDs, and can be raised to 60V maximum, which will reduce the supply current. Please refer to the Zetex ZXLD1360 and ZXLD1350 products for applications requiring input voltages lower than 30V.

The nominal current for the evaluation board is set at 700mA with a 0.15Ω sense resistor, R1.

The 68uH inductor used in the circuit is based on a 30V nominal supply, which should be connected across +VIN and GND pins.

Note: The evaluation board does not have reverse polarity protection. It is fitted with a 2.1mm DC power plug with positive to the centre pole.

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

Warning: with 700mA output, the connected LED will be hot and very bright

Figure 1: ZXLD1362EV3 evaluation board

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ZXLD1362 DEVICE DESCRIPTION

The ZXLD1362 is a continuous mode inductive driver in a TSOT23-5 package, for driving one or more series connected LEDs efficiently from a voltage source higher than the LED voltage. The device includes the output switch and a current sense circuit, which requires an external sense resistor to set the nominal current up to 1000mA.

ZXLD1362 DEVICE FEATURES

DEVICE APPLICATIONS

Drives one or more series-connected LEDs

LED flashlights.

• LEDs up to 1000mA.

• High Power LED driving.

Internal 60V switch.

• Low-voltage halogen replacement LEDs.

• Wide input voltage: 7V to 60V.

Automotive lighting.

• Inherent open circuit LED protection.

Illuminated signs.

Brightness control using DC or PWM.

Internal PWM filter.

ZXLD1362 Device Packages, Pin and Definitions

 

 

 

TSOT23-5 pack

ZXLD1362 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 a DC voltage (0.3V to 1.25V) or with a PWM signal to adjust

 

 

 

output current

 

 

 

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

ISENSE

4

 

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

 

 

 

output current. Nominal Iout = 0.1/ R1

VIN

5

 

Input voltage: 7V to 60V. Decouple to ground with a 100nF and a 10uF or

 

 

 

higher ceramic capacitor depending on the input voltage[1].

 

ORDERING INFORMATION

 

 

 

EVALBOARD ORDER NUMBER

DEVICE ORDER NUMBER

ZXLD1362EV3

 

ZXLD1362E5TA

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

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ZXLD1362EV3 EVALUATION BOARD

REFERENCE DESIGN

The ZXLD1362EV3 is configured to the reference design in Figure 2. The target application is a driver for one or more series-connected LEDs for luminaires in both commercial and automotive applications.

The maximum operating voltage is 60V, and the nominal current is set at 700mA with a 0.15Ω sense resistor R1. The device operates in continuous mode at approximately 150 kHz, with a 68uH inductor.

An accurate way of determining the current, avoiding the need to insert an ammeter in the current path, is to measure the voltage on the sense resistor. A 10K resistor and a 1uF capacitor can be used to form a low pass filter and the voltage across the capacitor represents a more stable dc reading of current. Using this method, 100mV represents 0.7 Amp when using a 0.15Ω sense resistor.

The ADJ pin connects to a low pass filter within the ZXLD1362 chip to provide some decoupling, but the external capacitor C2 (100nF) is used to provide additional decoupling to reduce any high frequency noise as well as enabling the soft start function.

Both DC and PWM dimming can be achieved by driving the ADJ pin. For DC dimming, the ADJ pin may be driven between 0.3V and 1.25V. Driving the ADJ pin below 0.2V will shut down 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 1 kHz, or high between 10 kHz to 50 kHz.

For low frequency, PWM capacitor C2 should be removed on the evaluation board, to give a more accurate duty cycle.

Shorting R2 will connect the test pin ADJ to device pin ADJ if needed.

The external capacitor C2 on the ADJ pin sets the soft start time. The amount of soft start time achievable is approximately 0.2ms/nF.

For other reference designs or further applications information, please refer to the ZXLD1362 datasheet.

Schematic Diagram

Figure 2 shows the schematic for the ZXLD1362EV3 evaluation board.

Vin

 

R1

LED A

 

4

 

5

 

 

 

C3

 

Vin

V sense

C1

C4

 

D1

 

 

ADJ

 

 

L1

R2

3

ZXLD1362

1

 

ADJ

LX

 

 

 

LED K

 

C2

GND

 

GND

 

 

 

Figure 2: Schematic for the evaluation board ZXLD1362EV3

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