IR3504MPBF International Rectifier, IR3504MPBF Datasheet - Page 21

• Manufacturer Part Number: IR3504MPBF
• Description: IC CTRL XPHASE AMD SVID 32-MLPQ
• Manufacturer: International Rectifier
• Series: XPhase3™r

Specifications of IR3504MPBF

• Applications: Processor
• Current - Supply: 10mA
• Voltage - Supply: 4.75 V ~ 7.5 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: *
• Package: 32-Lead MLPQ
• Circuit: X-Phase Control IC
• Switch Freq (khz): 250kHz to 1.5MHz
• Pbf: PbF Option Available
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Over-Current Hiccup Protection after Soft Start
The over current limit threshold is set by a resistor connected between OCSET
the hiccup over-current protection with delay after PG is asserted. The delay is required since over-current
conditions can occur as part of normal operation due to load transients or VID transitions.
If the IIN
voltage after PG is asserted, it will initiate the discharge of the capacitor at SS/DEL
47uA. If the over-current condition persists long enough for the SS/DEL
offset of the delay comparator, the fault latch will be set which will then pull the error amplifier’s output low to stop
phase IC switching and will also de-asserting the PG signal. The SS/DEL capacitor will then continue to be
discharged by a 4.5 uA current until it reaches 200 mV where the fault latch will reset to allow another soft start
cycle to occur. The output current is not controlled during the delay time. If an over-current condition is again
encountered during the soft start cycle, the over-current action will repeat and the converter will be in hiccup mode.
Linear Regulator Output (VCCL)
linear regulator. The output voltage of the linear regulator can be programmed between 4.75V and 7.5V by the
resistor divider at VCCLFB pin. The regulator output powers the gate drivers and other circuits of the phase ICs
along with circuits in the control IC, and the voltage is usually programmed to optimize the converter efficiency. The
linear regulator can be compensated by a 4.7uF capacitor at the VCCL pin. As with any linear regulator, due to
stability reasons, there is an upper limit to the maximum value of capacitor that can be used at this pin and it’s a
function of the number of phases used in the multiphase architecture and their switching frequency. Figure 14
shows the stability plots for the linear regulator with 5 phases switching at 750 kHz.
An external 5V can be connected to this pin to replace the linear regulator with appropriate selection of the VCCLFB
resistor divider, and VCCLDRV resistor. When using an external VCCL, it’s essential to adjust it such that VCCLFB
is slightly less than the 1.19V reference voltage. This condition ensures that the VCCLDRV pin doesn’t load the
ROSC pin. The switching frequency, FB1 bias current, VDAC slew rate and OCSET point are derived from the
loading current of ROSC pin.
The IR3504 has a built-in linear regulator controller, and only an external NPN transistor is needed to create a
Page 21
X
INTERNAL
OC DELAY
pin voltage, which is proportional to the average current plus VDAC
VRRDY
ENABLE
SS/DEL
IOUT
VOUT
EA
OCP THRESHOLD
3.92V
3.87V
4.0V
1.4V
START-UP WITH
OUTPUT SHORTED
Figure 13 Hiccup over-current waveforms
HICCUP OVER-CURRENT
PROTECTION (OUTPUT
SHORTED)
NORMAL
START-UP
NORMAL
OPERATION
(OUTPUT
SHORTED)
OCP
DELAY
X
capacitor to discharge below the 120mV
OVER-CURRENT
PROTECTION
(OUTPUT SHORTED)
X
and VDAC
X
X
voltage, exceeds the OCSETx
through the discharge current
NORMAL
START-UP
X
July 28, 2009
pins. Figure 13 shows
NORMAL
OPERATION
IR3504
POWER-DOWN