AAT1239-1_0810 Datasheet, PDF (19/23 Pages) Advanced Analogic Technologies – 40V Step-Up Converter for 4 to 10 White LEDs

SwitchReg^TM
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
PCB Layout Guidelines
Boost converter performance can be adversely affected
by poor layout. Possible impact includes high input and
output voltage ripple, poor EMI performance, and
reduced operating efficiency. Every attempt should be
made to optimize the layout in order to minimize para-
sitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1239-1
boost converter is shown in Figures 9 and 10. The fol-
lowing PCB layout guidelines should be considered:
1. Minimize the distance from Capacitor C1 and C2
negative terminal to the PGND pins. This is espe-
cially true with output capacitor C2, which conducts
high ripple current from the output diode back to the
PGND pins.
2. Minimize the distance between L1 to DS1 and
switching pin SW; minimize the size of the PCB area
connected to the SW pin.
3. Maintain a ground plane and connect to the IC PGND
pin(s) as well as the GND terminals of C1 and C2.
4. Consider additional PCB area on DS1 cathode to
maximize heatsinking capability. This may be neces-
sary when using a diode with a high V_F and/or ther-
mal resistance.
5. To avoid problems at startup, add a 10kΩ resistor
between the VIN, VP and EN/SET pins (R4). This is
critical in applications requiring immunity from input
noise during “hot plug” events, e.g. when plugged
into an active USB port.
Figure 9: AAT1239-1 Evaluation
Board Top Side Layout (with ten LEDs
and microcontroller).
Figure 10: AAT1239-1 Evaluation
Board Bottom Side Layout (with ten LEDs
and microcontroller).
1239-1.2008.10.1.2
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