ir3500a International Rectifier Corp., ir3500a Datasheet - Page 22

• Manufacturer Part Number: ir3500a
• Description: Xphase3 Vr11.0 & Amd Pvid Control Ic
• Manufacturer: International Rectifier Corp.

Linear Regulator Output (VCCL)
The IR3500A has a built-in linear regulator controller, and only an external NPN transistor is needed to create a
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
provides Bode 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. While using an external VCCL its essential to adjust it such that VCCLFB is
slightly lower than the 1.19V reference voltage. This condition ensures that the VCCLDRV pin doesn’t load the
ROSC pin. The switching frequency, VSETPT, and OCSET are derived from the loading current of ROSC pin.
INTERNAL
OC DELAY
VRRDY
ENABLE
SS/DEL
IOUT
EA
VOUT
OCP THRESHOLD
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3.92V
3.88V
4.0V
1.1V
START-UP WITH
OUTPUT SHORTED
Figure 14 - VCCL regulator stability with 5 phases and PHSOUT equals 750 kHz.
Figure 13 - Over Current Protection waveforms during and after soft start
HICCUP OVER-CURRENT
PROTECTION (OUTPUT
SHORTED)
NORMAL
START-UP
NORMAL
OPERATION
(OUTPUT
SHORTED)
OCP
DELAY
OVER-CURRENT
PROTECTION
(OUTPUT SHORTED)
NORMAL
START-UP
July 3, 2008
IR3500A
NORMAL
OPERATION
POWER-DOWN