LM20333EVAL National Semiconductor, LM20333EVAL Datasheet - Page 16

• Manufacturer Part Number: LM20333EVAL
• Description: EVALUATION BOARD FOR THE LM20333
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM20333EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 3A
• Voltage - Input: 4.5 ~ 25V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: LM20333
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -

www.national.com
FIGURE 8. Safe Thermal Operating Areas (I
FIGURE 9. Safe Thermal Operating Areas (I
FIGURE 10. Safe Thermal Operating Areas (I
f
SW
= 350kHz)
= 500kHz)
= 750kHz)
OUT
OUT
30051690
30051688
30051689
OUT
= 3A, f
= 3A, f
= 3A,
SW
SW
16
The dashed lines in the figures above show an approximation
of the minimum and maximum duty cycle limitations; while,
the solid lines define areas of operation for a given ambient
temperature. This data for the figure was derived assuming
the device is operating at 3A continuous output current on a
4 layer PCB with a copper area greater than 4 square inches
exhibiting a thermal characteristic less than 27 °C/W. Since
the internal losses are dominated by the FETs a slight reduc-
tion in current by 500mA allows for much larger regions of
operation, as shown in Figure 11.
Figure 12, shown below, provides a better approximation of
the θ
test consisted of 4 layers: 1oz. copper was used for the inter-
nal layers while the external layers were plated to 2oz. copper
weight. To provide an optimal thermal connection, a 5 x 4 ar-
ray of 12 mil thermal vias located under the thermal pad was
used to connect the 4 layers.
PCB LAYOUT CONSIDERATIONS
PC board layout is an important part of DC-DC converter de-
sign. Poor board layout can disrupt the performance of a DC-
DC converter and surrounding circuitry by contributing to EMI,
FIGURE 11. Safe Thermal Operating Areas (I
FIGURE 12. Thermal Resistance vs PCB Area (4 Layer
JA
for a given PCB copper area. The PCB used in this
f
SW
Board)
= 500kHz)
30051691
30051687
OUT
= 2.5A,