ZXLD1356

ZXLD1356

Document number: DS33470 Rev. 3 - 2

25 of 29

www.diodes.com

December 2010

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Layout Considerations

LX pin

The LX pin of the device is a fast switching node, so PCB tracks should be kept as short as possible. To minimize ground

'bounce', the ground pin of the device should be soldered directly to the ground plane.

Coil and decoupling capacitors and current sense resistor

It is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as possible to minimize

parasitic resistance and inductance, which will degrade efficiency. It is also important to minimize any track resistance in series

no other currents flowing in these tracks. It is important that the cathode current of the Schottky diode does not flow in a track

ADJ pin

The ADJ pin is a high impedance input for voltages up to 1.35V so, when left floating, PCB tracks to this pin should be as short

as possible to reduce noise pickup. A 100nF capacitor from the ADJ pin to ground will reduce frequency modulation of the output

under these conditions. An additional series 3.3k

Ω resistor can also be used when driving the ADJ pin from an external circuit

(see below). This resistor will provide filtering for low frequency noise and provide protection against high voltage transients.

High voltage tracks

Avoid running any high voltage tracks close to the ADJ pin, to reduce the risk of leakage currents due to board contamination.

The ADJ pin is soft-clamped for voltages above 1.35V to desensitize it to leakage that might raise the ADJ pin voltage and cause

excessive output current. However, a ground ring placed around the ADJ pin is recommended to minimize changes in output

current under these conditions.

Evaluation Boards

ZXLD1356 evaluation boards are available on request, which have connection terminals that allow customers to connect their

own LED products to the board.

GND

ZXLD1356

ADJ

3.3k

100nF

GND