ir3084a International Rectifier Corp., ir3084a Datasheet - Page 18

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

Figure 10a depicts the start-up sequence without AVP in Boot Mode (VRM11)
grounded. First, the VDAC pin is charged to the 1.1V Boot voltage. Then, if there are no fault conditions, the
SS/DEL capacitor will begin to be charged. Initially, the error amplifier’s output will be clamped low until the
voltage at the SS/DEL pin reaches 1.3V. After the voltage at the SS/DEL pin rises to 1.3V, the error amplifier’s
output will begin to rise and the converter’s output voltage will be regulated 1.3V below the voltage at the SS/DEL
pin. The converter’s output voltage will slowly ramp to the 1.1V Boot voltage. The SS/DEL pin’s voltage will
continue to increase until it rises above the 3.1V threshold of the VID delay comparator. When the SS/DEL
voltage exceeds 3.1V, the VID inputs will be sampled and the VDAC pin will transition to the level determined by
the VID inputs at the dynamic VID slew rate. When the voltage on the SS/DEL pin rises above 3.77V the VRRDY
Delay Comparator will allow the VRRDY signal to be asserted. SS/DEL will continue to rise until finally settling at
3.85V, indicating the end of the start-up sequence.
Figure 10b depicts the start-up sequence in Non-Boot Mode
(12V). First, the external VID setting is sampled and the VDAC pin is set to the desired VID voltage. Then, if
there are no fault conditions, the SS/DEL capacitor will begin to charge. Initially, the error amplifier’s output will
be clamped low until the voltage at the SS/DEL rises to 1.3V. After the voltage at the SS/DEL pin reaches 1.3V,
the error amplifier’s output will begin to rise and the converter’s output voltage will be regulated 1.3V below the
voltage at the SS/DEL pin. As the voltage at the SS/DEL pin continues to rise, the converter’s output voltage will
slowly increase until it is equal to the voltage at the VDAC pin. When the voltage on the SS/DEL pin rises above
3.77V the VRRDY Delay Comparator will allow the VRRDY signal to be asserted. SS/DEL will continue to rise
until finally settling at 3.85V, indicating the end of the start up sequence.
If AVP is used (RDRP
amplifier to the Error Amplifier’s FB pin. During startup with AVP, the VDRP amplifier will produce a voltage at
the FB pin equal to VDAC times the resistor divider formed by the droop resistor and the feedback resistor from
Vcore to the FB pin. To offset the contribution from the VDRP amplifier, the voltage at the SS/DEL pin will have
to rise to beyond 1.3V before the Error Amplifier’s output and Vcore begin to rise. For a DAC setting of 1.3V with
typical load line slope, the Error Amplifier’s output will begin to rise when the voltage at the SS/DEL pin reaches
approximately 1.6V. The effect of this offset will be to slightly lengthen the Start Delay (TD1) and shorten the Soft
Start Ramp Time (TD2).
The following table summarizes the differences between the 4 modes associated with setting the VIDSEL pin. In
addition to changing the soft start sequence, the NO_CPU code may or may not be ignored during startup and
the NO_CPU code may or may not be latched.
Page 18 of 45
FLOAT (1.2V)
VBIAS (6.9V)
VCC (12V)
VIDSEL
Voltage
GND
Table 3: 3084A Controller Functionality versus VIDSEL Voltages
, the soft start timing will change slightly because of the resistor from the VDRP
Table
VR10
VR11
VR11
VR10
VID
Voltage During
1.1V Boot
Startup?
YES
YES
NO
NO
VIDSEL is connected to VBIAS (6.9V) or to VCC
Ignore NO CPU
Codes During
Startup?
YES
YES
NO
NO
VIDSEL is either floating or
Latch NO CPU
Fault Code?
IR3084A
YES
YES
NO
NO
10/30/2006