ncp5389 ON Semiconductor, ncp5389 Datasheet - Page 21

• Manufacturer Part Number: ncp5389
• Description: 2/3 Phase Buck Controller For Vr11 Pentium Iv Processor Applications
• Manufacturer: ON Semiconductor

Dynamic VID Testing
Intel Requirements. Select the Dynamic VID option.
Before enabling the test set the lowest VID to 0.5 V or
greater and set the highest VID to a value that is greater than
the lowest VID selection, then enable the test. See Figures
10 through 12.
The VTT tool provides for VID stepping based on the
Figure 12. Dynamic VID Settling Time Falling
Figure 11. Dynamic VID Settling Time Rising
Figure 10. 1.6 to 0.5 Dynamic VID Response
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NCP5389
21
Design Methodology
Decoupling the V
minimize supply noise on the IC. The resistor should be
sized such that it does not generate a large voltage drop
between the 12 V supply and the IC. See the schematic
values.
Understanding Soft-Start
capture the VID code then resume ramping to target value
based on an internal slew rate limit. See Figure 13. The
controller is designed to regulate to the voltage on the SS
pin until it reaches the internal DAC voltage. The soft-start
cap sets the initial ramp rate using a typical 5.0 mA current.
The typical value to use for the soft-start cap (SS), is
typically set to 0.01 mF. This results in a ramp time to 1.1 V
of 2.2 ms based on equation 1.
An RC input filter is required as shown in the V
The controller will ramp to the 1.1 V, with a pause to
C ss ^ i ss
2.2 · ms
C ss + 0.01 · mF
1.1 · V
Figure 13. VR11 Startup
CC
+
Pin on the IC
dv ss
dt ss
dv ss
dt ss
and i ss + 5 · mA
CC
(eq. 1)
pin to