M51995AFP-CF0J Datasheet, PDF (39/43 Pages) Renesas Technology Corp – Switching Regulator Control

M51995AP/AFP
DET Circuit
Figure 41 shows how to use the DET circuit for the voltage detector and error amplifier.
M51995A
C
C1
F/B
C2 R3
DET
C4
A
Detecting
voltage
R1
B
R2
Figure 41 How to use the DET Circuit for the Voltage Detector
For the phase shift compensation, it is recommended to connected the CR network between DET terminal and F/B
terminal.
Figure 42 shows the gain-frequency characteristics between point B and point C shown in figure 41.
G_AVDET
(DC Voltage gain)
G1
Log ω
ω₁
ω₂
Figure 42 Gain-Frequency Characteristics between Point B and C shown in Figure 41
The G1, ω₁ and ω₂ are given by following equations;
G1 =
R3
R1 / R2
………………………
(12)
ω₁
=
1
C2 • R3
………………………… (13)
ω₂ =
C1 + C2
C1 • C2 • R3
………………… (14)
At the start of the operation, there happen to be no output pulse due to F/B terminal current through C1 and C2, as the
potential of F/B terminal rises sharply just after the start of the operation.
Not to lack the output pulse, is recommended to connect the capacitor C4 as shown by broken line.
Please take notice that the current flows through the R1 and R2 are superposed to I_CC(START). Not to superpose, R1 is
connected to C_VCC2 as shown in figure 25.
REJ03D0835-0300 Rev.3.00 Jun 06, 2008
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