zxld1360 Zetex Semiconductors plc., zxld1360 Datasheet - Page 23

• Manufacturer Part Number: zxld1360
• Description: 1a Led Driver With Internal Switch
• Manufacturer: Zetex Semiconductors plc.

ZXLD1360
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
RS. Its best to connect V
directly to one end of R
and Isense directly to the opposite end of RS
IN
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 10k 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.
10k
ZXLD1360
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
The ZXLD1360EV1, 2 or 3 evaluation boards are available on request. These boards contain a
Lumileds K2 or multiple Ostar LEW type LEDs to allow quick testing of the 1360 device. Additional
terminals allow for interfacing to customers own LED products.
Issue 1 - March 2007
23
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© Zetex Semiconductors plc 2007