ncp1582 ON Semiconductor, ncp1582 Datasheet - Page 11

• Manufacturer Part Number: ncp1582
• Description: Low Voltage Synchronous Buck Controller
• Manufacturer: ON Semiconductor

Design Example
Choose the loop gain crossover frequency;
The corner frequency of the output filter is calculated
below;
Check that the ESR zero frequency is not too high;
Zero of the compensation network is calculated as
follows;
capacitor. By adjusting the value of this compensation
capacitor, the soft start time can be adjusted.
F Z + F LC
C C +
+
Switching Frequency F
Output Capacitance C
Output Capacitance C
Output Inductance L
Input Voltage V
Output Voltage V
Let R
This condition is mandatory for loop stability.
The compensation capacitor also acts as the soft start
2 * p * 2.3 kHz * 1500
F LC +
C
2 * p * F Z * R C
= 1500
F ESR +
2 * p * 0.75 mH * 6630 mF
1
1
F CO + 1
in
out
= 12 V
2 * p @ CESR @ C O
= 3.3 V
out
10
ESR
out
SW
+ 46 nF
= 0.75 mH
1
* F SW + 35 kHz
= 6630 mF
= 45 mW/Each
1
= 350 KHZ
t
NCP1582, NCP1582A, NCP1583
+ 2.3 kHz
F SW
5
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11
Pole of the compensation network is calculated as
follows;
R
analyzer is shown below.
C
The recommended compensation values are;
The NCP158x bode plot as measured from the network
= 1500, C
Figure 15. Typical Bode plot of the Open−loop
Top plot: Phase−Frequency (Phase Margin = 62.519°)
Bottom plot: Gain−Frequency (UGBW= 5 MHz)
Frequency Response of the NCP158x
+
C
2 * p * 175 kHz * 1500
= 46 nF, C
F P + 5 * F CO + 175 kHz
C P +
1
2 * p * F P * R C
P
= 700 pF
1
+ 700 pF