User Guide 033
UG033.0
June 19, 2015
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3
Soft-start Control
Short CSS to SGND for internal soft-start (approximately 1ms).
Populate CSS to adjust the soft-start time. This capacitor, along
with an internal 1.6µA current source, sets the soft-start interval
of the converter, t
SS
.
CSS must be less than 33nF to insure proper soft-start reset after
fault condition.
Switches Control
The ISL8026EVAL3Z and ISL8026AEVAL3Z boards contain SW1
and SW2 for various controls of the ISL8026, ISL8026A
circuitries.
Table 1
details this function.
PCB Layout Recommendation
The PCB layout is a very important converter design step to make
sure the designed converter works well. For ISL8026, ISL8026A,
the power loop is composed of the output inductor L’s, the output
capacitor (COUT), the PHASE pins and the PGND pin. It is
necessary to make the power loop as small as possible and the
connecting traces among them should be direct, short and wide.
The switching node of the converter, the PHASE pins and the
traces connected to the node are very noisy, so keep the voltage
feedback trace away from these noisy traces. The input capacitor
should be placed as close as possible to the VIN pin. The ground
of input and output capacitors should be connected as close as
possible. The heat of the IC is mainly dissipated through the
thermal pad. Maximizing the copper area connected to the
thermal pad is preferable. In addition, a solid ground plane is
helpful for better EMI performance. It is recommended to add at
least 5 vias ground connection within the pad for the best
thermal relief.
TABLE 1. SWITCH SETTINGS
SW1
ENABLE
FUNCTION
1
OFF
DISABLE VO
3
ON
ENABLE VO
SW2
MODE
FUNCTION
1
PWM
Fixed PWM frequency at light
load
3
PFM
Force continuous mode
CSS
F
3.33 t
SS
s
=
(EQ. 3)
