ir3084a International Rectifier Corp., ir3084a Datasheet - Page 17

• Manufacturer Part Number: ir3084a
• Description: Xphase Tm Vr 10/11 Control Ic
• Manufacturer: International Rectifier Corp.

Inductor DCR Temperature Correction
If the thermal compensation of the inductor DCR provided by the temperature dependent gain of the current
sense amplifier is not adequate, a negative temperature coefficient (NTC) thermistor can be used for additional
correction. The thermistor should be placed close to the inductor and connected in parallel with the feedback
resistor, as shown in Figure 9. The resistor in series with the thermistor is used to reduce the nonlinearity of the
thermistor.
Remote Voltage Sensing
To compensate for impedance in the ground plane, the VOSNS pin is used for remote sensing and connects
directly to the load. The VDAC voltage is referenced to VOSNS to avoid additional error terms or delay related
to a separate differential amplifier. The capacitor connecting the VDAC and VOSNS pins ensure that high speed
transients are fed directly into the error amp without delay.
Start-up Modes
The IR3084A has a programmable soft-start function to limit the surge current during the converter start-up. A
capacitor connected between the SS/DEL and LGND pins controls soft start as well as over-current protection
delay and hiccup mode timing. A charge current of 70uA controls the positive slope of the voltage at the SS/DEL
pin.
There are two types of start-up possible: Boot Mode (VR11) and Non-Boot Mode (legacy VR10). In Boot Mode,
the soft start circuitry will initially set the voltage at the VDAC pin to 1.1V and the converter’s output will slowly
rise, using the slew rate set by the capacitor at the SS/DEL pin, until it’s equal to 1.1V. After Vcore achieves the
1.1V Boot voltage, there will be a short delay, the VID pins will be sampled, and the voltage at the VDAC pin and
the converter’s output will increase or decrease to the desired VID setting using the dynamic VID slew rate. In
Non-Boot Mode, the soft start sequence will ramp the voltage at the VDAC pin directly to the external VID setting
using the slew rate set by the capacitor at the SS/DEL pin without pausing at the 1.1V Boot voltage.
Page 17 of 45
Figure 9
IOFFSET
Temperature compensation of inductor DCR
Control IC
AVP
Amplifier
VDAC
Error
Amplifier
+
-
-
+
RSETPT
VSETPT
EAOUT
VDRP
IIN
IIN
RDRP
RFB2
RFB
Rt
Vo
IR3084A
10/30/2006