ZXLD1362

Provisional version B - July 2007

28

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© Zetex Semiconductors plc 2007

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 with current sense resistor

with no other currents flowing in these tracks. It is important that the cathode current of the

measure of current than is actual because of track resistance.

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

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 PCB

ZXLD1362 evaluation boards are available on request. These boards contain LEDs to allow quick

testing of the 1362 device. Additional terminals allow for interfacing to customers own LED

products.

GND

ZXLD1362

ADJ

3.3k

100nF

GND