SI6552DQ_ データシートの表示（PDF） - Vishay Semiconductors
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SI6552DQ_ Datasheet PDF : 7 Pages
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AN805
Vishay Siliconix
A power MOSFET is made up of many single MOSFET cells
arranged in a parallel combination. In an ideal MOSFET all the
cells will turn on together when activated by a gate signal, and a
minimum switching time transition will be obtained. This does not
happen in a conventional MOSFET layout because the gate signal
has to propagate across the silicon in a turn-on “wave,” where the
cells nearest the gate bus turn on first with the outer cells following.
The PWM optimized MOSFET has symmetrical gate bussing, and
its bonding and layout structures minimize the turn-on “wave,” thus
increasing the switching speed of the device.
Efficiency
How much extra efficiency does the PWM optimized MOSFET
provide? A comparison of the efficiency of the synchronous boost
converter (Figure 4) using three different MOSFET technologies
shows that an improvement on the order of 5% can be made if an
optimized device is used.
100.00
Figures 6, 7, and 8 show efficiency at switching frequencies
ranging from 300 kHz to 1.8 MHz, while Figure 9 summarizes the
efficiencies of the three technologies against switching frequency
at an output current of 400 mA. For all the results shown, the input
voltage for the synchronous boost converter was 3.6 V, with an
output voltage of 5 V.
The PWM optimized MOSFET surpasses all other technologies
while maintaining the highest efficiencies over the broadest load
ranges at all switching frequencies. The conventional MOSFET
technology provides the same breadth of efficiency but at a
reduced value. The low- threshold technology is clearly unsuited to
switching at higher switching frequencies with a gate voltage of
4.5 V.
As summarized in Table 1, at all switching frequencies the PWM
optimized MOSFET technology gives superior performance, both
in highest peak efficiencies and over the broadest load range,
making it the ideal choice for most low-voltage dc-to-dc designs.
100.00
90.00
90.00
h% 80.00
70.00
60.00
0.0
h % 6801 300 kHz
h % 6542 300 kHz
h % 6552 300 kHz
200.0 400.0 600.0 800.0 1000.0
Output Current 0 to 1000 mA
FIGURE 6. Efficiency comparison between high-frequency,
conventional, and low-threshold MOSFETs at a
switching frequency of 300 kHz.
80.00
h%
70.00
60.00
0.0
h % 6801 1 kHz
h % 6542 1 kHz
h % 6552 1 kHz
200.0 400.0 600.0 800.0 1000.0
Output Current 0 to 1000mA
FIGURE 7. Efficiency comparison between high-frequency,
conventional and low-threshold MOSFETs at a
switching frequency of 300 kHz
100.00
90.00
80.00
h%
70.00
60.00
0.0
h % 6801 1.8 MHz
h % 6542 1.8 MHz
h % 6552 1.8 MHz
200.0 400.0 600.0 800.0 1000.0
Output Current 0 to 1000mA
FIGURE 8. Efficiency comparison between high-frequency,
conventional, and low-threshold MOSFETs at a
switching frequency of 1.8 MHz.
Document Number: 70649
January 1997
100
95
90
h% 85
80
75
70
0
h % 6801 400 mA
h % 6542 400 mA
h % 6552 400 mA
500 1000 1500 2000
Switching Frequency (kHz)
FIGURE 9. Efficiency vs. switching frequency comparing the
PWM optimized MOSFET technology with
conventional and low-threshold technologies
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