zxld1366 Zetex Semiconductors plc., zxld1366 Datasheet - Page 28

• Manufacturer Part Number: zxld1366
• Description: High Accuracy 1a, 60v Led Driver With Internal Switch
• Manufacturer: Zetex Semiconductors plc.

ZXLD1366
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
R
. Its best to connect V
directly to one end of R
and Isense directly to the opposite end of R
S
IN
S
S
with no other currents flowing in these tracks. It is important that the cathode current of the
Schottky diode does not flow in a track between R
and V
as this may give an apparent higher
S
IN
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.
3.3k
ZXLD1366
ADJ
GND
100nF
GND
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
ZXLD1366 evaluation boards are available on request. Terminals allow for interfacing to
customers own LED products.
Issue 2 - September 2008
28
www.zetex.com
www.diodes.com
© Diodes Incorporated 2008