MB39A132QN-G-ERE1 Datasheet, PDF (43/56 Pages) Fujitsu Component Limited. – ASSP For Power Management Applications (Rechargeable Battery) Synchronous Rectification DC/DC Converter IC for Charging Li-ion Battery

MB39A132
• Design of phase compensation circuit
(1) Constant voltage (CV) mode phase compensation circuit
When a low-ESR capacitor, such as a ceramic capacitor, is used as the output capacitor, it is easier for the
DC/DC converter to oscillate as the phase delay approaches 180 degrees due to the resonance frequency
of LC. In this situation, perform phase compensation by connecting a RC phase lead compensator between
the -INE3 pin (pin 6) and the COMP3 pin (pin 16), and between the -INE3 pin (pin 6) and the BATT pin (pin 17) .
2pole-2zero phase compensation circuit
VO
BATT
CZ1
17
6
CZ2 RZ2
-INE3
R1
-
16
R2
+
COMP3
Error Amp3
Vrefint1
To PWM Comp.
The constant for the phase lead compensation circuit can be found by the following formula.
5.1 × 10 − ⁶
CZ1 =:
(2 × CELLS − 1) fLC
RZ2 =: 8.9 × 10⁴ ×
fCO
VIN × fLC
+ 3600
1
CZ2 =:
2π × RZ2 × fLC
CELLS : Number of battery series cells
fLC : Resonance frequency of inductor and output capacitor [Hz]
VIN : Switching power supply voltage [V]
fCO : Crossover frequency [Hz]
As for the crossover frequency (fco) indicating the bandwidth of the control loop of the DC/DC converter,
while a high crossover frequency is good for quick response, it increases the risk of oscillation due to an
insufficient phase margin.
Though this crossover frequency can be freely set, keep the frequency in the range of 1/10-1/5 of the switching
frequency (fosc) whenever possible.
DS04–27265–3E
43