Datasheet

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SLUS486B − AUGUST 2001 − REVISED JULY 2003
16
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APPLICATION INFORMATION
Complementary
Gate Drive
Waveforms
2 V / div
VDS of SR
MOSFET
Switch
2 V / div
Adaptive Drive
20 ns / div
Predictive Drive
20 ns / div
B
C
A
A4
B4
C4
Figure 10. Close-Up: Turn-Off of Synchronous Rectifier Switch to Turn-On of Main Switch
Complementary
Gate Drive
Waveforms
2 V / div
Adaptive Drive
20 ns / div
Predictive Drive
20 ns / div
VDS of SR
MOSFET
Switch
2 V / div
D
D4
E
E4
Figure 11. Close-Up: Turn-Off of Main Switch to Turn-On of Synchronous Rectifier Switch
efficiency comparison
Figures 12 through 15 show a series of efficiency measurements taken at two output voltages (0.9 V and 1.8
V) and two switching frequencies (250 kHz and 500 kHz) for both predictive and adaptive delay techniques.
The efficiency gain using the predictive technique is 1% for a V
OUT
level of 1.8 V and at a switching frequency
of 250 kHz (Figure 12). Figures 13 and 14 show the efficiency gain approximately doubles when V
OUT
is lowered
by a factor of two (to 0.9 V), or when the switching frequency is doubled to 500 kHz. With both doubled frequency
and one-half of the output voltage, the efficiency gain of predictive technology is about 4% over the adaptive
technology (Figure 15). Therefore, as the switching frequency increases and output voltages are lowered, the
efficiency gains are higher. This results in lower operational temperatures for increased reliability as well as
smaller size designs for increased frequencies.