YB1692 Datasheet, PDF (7/10 Pages) YOBON TECHNOLOGIES,INC. – 2A Synchronous Step-Down Converter

YB1692
2A Synchronous Step-Down Converter
The goal of compensation design is to shape
the converter transfer function to get a desired
loop gain. The system crossover frequency
where the feedback loop has the unity gain is
important. Lower crossover frequencies result
in slower line and load transient responses,
while higher crossover frequencies could
cause system insta- bility. A good rule of
thumb is to set the cross- over frequency
below one-tenth of the switching frequency.
To optimize the compensation components,
the following procedure can be used.
1.Choose the compensation resistor (R3) to
set the desired crossover frequency.
Determine the R3 value by the following
equation:
Where fC is the desired crossover frequency
which is typically below one tenth of the
switch- ing frequency.
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applica- tions with typical inductor values,
setting the compensation zero, fZ1, below
one-forth of the crossover frequency provides
sufficient phase margin.Determine the C3
value by the following equa- tion:
Where R3 is the compensation resistor.
3. Determine if the second compensation
capacitor (C6) is required. It is required if the
ESR zero of the output capacitor is located at
less than half of the switching frequency, or
the following rela- tionship is valid:
If this is the case, then add the second
compensation capacitor (C6) to set the pole
fP3 at the location of the ESR zero.
Determine the C6 value by the equation:
External Bootstrap Diode
It is recommended that an external bootstrap
diode be added when the system has a 5V
fixed input or the power supply generates a
5V output. This helps im- prove the efficiency
ofthe regulator. The bootstrap diode can be a
low cost one such as IN4148 or BAT54.
Figure 4 External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when
)output
voltage (VOUT>12V) applications.
Typical Performance Characteristics
Figure 5 YB1692 with AVX 47μF, 6.3V Ceramic Output Capacitor
YB1692 Rev.1.0
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