IR3094PBF Datasheet, PDF (21/29 Pages) International Rectifier – 3 PHASE PWM CONTROLLER FOR POINT OF LOAD

IR3094PBF
VO+
RFB
VDRP
RDRP
CCP1
RCP
CCP
FB _-
EAOUT
V_VR_DE_AF_{C +}
EAOUT
CCP1
RFB
VO+
RFB1 CFB
VDRP
RDRP
CDRP
RCP
CCP
FB
V^VD^RA^EC^F
-
EAOUT
+
EAOUT
(a) Type II compensation
(b) Type III compensation
Figure 9. Voltage loop compensation networks
Type II Compensation for Voltage Droop Applications
Determine the compensation at no load, the worst case condition. Choose the crossover frequency fc between 1/10
and 1/5 of the switching frequency per phase. Assume the time constant of the resistor and capacitor across the
output inductors matches that of the inductor, and determine RCP and CCP from (16) and (17), where LE and CE are
the equivalent inductance of output inductors and the equivalent capacitance of output capacitors respectively.
R_CP
(2S f _C ) ² L_E C_E R_FB 5
V_I * 1 (2S * f _C *C * R_C ) ²
(16)
C _CP
10 L_E C_E
R_CP
(17)
CCP1 is optional and may be needed in some applications to reduce the jitter caused by the high frequency noise. A
ceramic capacitor between 10pF and 220pF is usually enough.
Type III Compensation for Voltage Droop Applications
Determine the compensation at no load, the worst case condition. Assume the time constant of the resistor and
capacitor across the output inductors matches that of the inductor, the crossover frequency and phase margin of the
voltage loop can be estimated by (18) and (19), where RLE is the equivalent resistance of inductor DCR.
f _C1
R _DRP
2S *C_E G_CS * R_FB R_LE
(18)
T
C1
90

A
tan(0.5)

180
S
(19)
Choose the desired crossover frequency fc around fc1 estimated by (18) or choose fc between 1/10 and 1/5 of the
switching frequency per phase, and select the components to ensure the slope of close loop gain is -20dB /Dec
around the crossover frequency. Choose resistor RFB1 according to (20), and determine CFB and CDRP from (21)
and (22).
Page 21 of 29
09/26/05