r2j20751np Renesas Electronics Corporation., r2j20751np Datasheet - Page 11

• Manufacturer Part Number: r2j20751np
• Description: Peak Current Mode Synchronous Buck Controller With Power Mos Fets
• Manufacturer: Renesas Electronics Corporation.

R2J20751NP
Output Voltage Setting
The error amplifier of the device has an accurate 0.6 V reference voltage and REFIN pin which can input reference
voltage from external voltage. When reference voltage is 0.6 V, feedback loop leads to the FB pin a voltage of 0.6 V in
case of stable condition on the converter. Therefore the output voltage is;
REFIN pin should be pulled up to VCIN, when reference voltage refer to internal 0.6 V.
Loop Compensation
Peak-current control makes design in terms of phase margins easier than is the case with voltage control. This is
because of differences between the characteristics of the PWM modulator and power stage in the two methods.
Figure 1 and 2 shows the behavior of the PWM modulator and power stage in the case of voltage control and peak
current control, respectively.
Feed-forward current to the modulator in the case of peak-current control means that the system is single pole, so we
see a –20 dB/decade cutoff and phase margin of 90° in the Bode plot. In voltage control, the system configures a two-
pole system. That is why rather complicated loop compensation of the error amplifier is required. Such as type-III
compensation. The design of effective compensation is thus much simpler in the case of peak-current control (refer to
figure 3).
R07DS0240EJ0100 Rev.1.00
Jan 26, 2011
Gain
(dB)
Phase
(deg)
Vout = 0.6 V  (R1 + R2) / R2
Figure 1 Bode Plot (Voltage Mode)
180
0
R
REFIN
freq. (Hz)
freq. (Hz)
VCIN
40 dB/dec
CT
FB
Gain
(dB)
Phase
(deg)
Figure 2 Bode Plot (Peak Curent Mode)
180
90
0
Vout
R1
R2
freq. (Hz)
freq. (Hz)
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Preliminary
20 dB/dec