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CXW8508 View Datasheet(PDF) - Unspecified

Part NameDescriptionManufacturer
CXW8508 CXW8508 - SOP8 PIN ETC
Unspecified 
CXW8508 Datasheet PDF : 9 Pages
1 2 3 4 5 6 7 8 9
深圳市诚芯微科技有限公司                      CX8508
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.
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:
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:
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 of the regulator. The bootstrap
diode can be a low cost one such as IN4148 or
BAT54.
CX8508
Where R3 is the compensation resistor.
3. Determine if the second compensation
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty cycle
operation when output voltage (VOUT>12V)
applications
7
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