UM0422

Description of the board

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The current regulation is accomplished by regulating the voltage across a current sense

resistor. The EVM does not operate correctly unless a load is placed between (J1-A) and

(J1-K). No-load condition is indicated by the turn-on of the LED D1. The EVM allows the

user to place one Lumileds LED LXHLPW09 directly soldered on the board. A different or a

higher number of LEDs may be used externally, by connecting the LED anode to J1-A and

the LED cathode to J1-K.

The evaluation board embeds an internal oscillator able to implement a PWM dimming

technique. The board gives the user the possibility to change both the frequency and the

duty cycle of the PWM signal using the corresponding R8 and R9 trimmer. The user is able

to change the average current on the LEDs branch by modifying the duty cycle of the PWM

signal between 0% to 100% using the R9 trimmer.

It is possible to send an external PWM signal to the PWM pin. This operation is

accomplished by providing the PWM signal between the PWM and GND pins of the J4

connector and keeping the J3 connector floating.

4.1

Input/output connections

Table 3 describes the input/output connections.

Table 3.

Input/output connections

Reference

designator

Name

Description

J1

Vin/LEDs

– Positive and negative connections to the input power supply

[4.5 V, 40 V].

If LED is mounted on the evaluation board:

If external LEDs are used:

– Connecting the LEDs chain between A and K pins.

J2

Enable

Use this connector to enable and disable the controller.

– EN and the 5 V pins shorted to enable the controller.

– EN and the GND pins shorted to disable the controller.

– If EN pin is left open, the EVM does not operate correctly.