IR3094M International Rectifier Corp., IR3094M Datasheet - Page 15

• Manufacturer Part Number: IR3094M
• Description: 3 Phase Pwm Controller For Point Of Load
• Manufacturer: International Rectifier Corp.

RFB
APPLICATIONS INFORMATION
Oscillator Resistor R
The oscillator frequency is programmable from 100kHz to 540kHz with an external resistor R
Figure 6. The Oscillator generates an internal 50% duty cycle sawtooth signal (Figure 3.) that is used to generate
120° out-of-phase timing pulses to set Phase 1,2 and 3 RS flip-flops. Once the switching frequency is chosen,
R
Soft Start, Over-Current Fault Delay, and Hiccup Mode
The IR3094 has a programmable soft-start function to limit the surge current during converter power-up. A capacitor
connected between the SS/DEL and LGND pins controls soft start timing as well as over-current protection delay
and hiccup mode timing.
Figure 8 depicts the various operating modes of the SS/DEL function. Under a no fault condition, the SS/DEL
capacitor will charge. The SS/DEL charge soft-start duration is controlled by a 60uA charge current which charges
CSS up to 4.0V. The Error Amplifier output is clamped low until SS/DEL reaches 1.1V. The Error Amplifier will then
regulate the converter’s output voltage to match the SS/DEL voltage less the 1.1V offset until it reaches the level
determined by the VREF voltage. The PWRGD signal is asserted once the SS/DEL voltage exceeds 3.75V.
Four different faults will immediately cause SS/DEL to begin discharging and set the Fault Latch once SS/DEL is
below 3.75V;
GND
ROSC
VIN
RCOMP
CVIN
CREF
RREF
can be determined from the curve in the Typical Operating Characteristics Section.
Page 15 of 29
CCOMP
CSS
ROCSET
CSC2
RSC2
RDRP
RROSC
CSC3
RSC3
PGOOD
ENABLE
VOUT+
ROSC
OVP
C5VREF
RSET
Cosns-
NC
NC
ROSC
VOSNS-
OCSET
VREF
VDRP
FB
EAOUT
SS/DEL
SCOMP2
SCOMP3
VIN
CVCC
IR3094
48LD MLPQ
Figure 6 – System Diagram
VCCL1_2
GATEH1
GATEH2
GATEH3
GATEL1
GATEL2
PGND1
PGND2
VCCH2
VCCH3
PGND3
5VUVL
CBIAS
CBST3
CBST1
CBST2
VIN
RCS3
1
VIN
VIN
L3
RCS1
1
CCS3
1
RCS2
2
L1
L2
CCS1
CCS2
2
2
IR3094PBF
ROSC
09/26/05
COUT
as shown in
VOUT SENSE+
VOUT SENSE-
VOUT+
GND