ISL8033 데이터 시트보기 (PDF) - Intersil
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ISL8033 Datasheet PDF : 18 Pages
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ISL8033, ISL8033A
relative to the internal reference voltage and feed it back to the
inverting input of the error amplifier. Refer to Figure 2.
The output voltage programming resistor, R2 (or R5 in Channel
2), will depend on the desired output voltage of the regulator. The
value for the feedback resistor is typically between 0Ω and
750kΩ. Let R2 = 124kΩ, then R3 will be:
R3
=
-----R----2---x---0----.-8----V------
VOUT – 0.8V
(EQ. 2)
For better performance, add 12pF in parallel to R2. If the output
voltage desired is 0.8V, then leave R3 unpopulated and short R2.
Input Capacitor Selection
The main functions for the input capacitor is to provide
decoupling of the parasitic inductance and to provide filtering
function to prevent the switching current flowing back to the
battery rail. One 22µF X5R or X7R ceramic capacitor is a good
starting point for the input capacitor selection per channel.
PCB Layout Recommendation
The PCB layout is a very important converter design step to make
sure the designed converter works well. For ISL8033, the power
loop is composed of the output inductor L’s, the output capacitor
COUT1 and COUT2, the LX’s pins, and the SGND 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 LX_ 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 closely as possible to the VIN pin . Also, the
ground of the input and output capacitors should be connected
as closely 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.
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16
FN6854.2
March 24, 2011
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