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NCP5391MNR2G

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NCP5391
http://onsemi.com
19
APPLICATION INFORMATION
The NCP5391 is a high performance multiphase
controller optimized to meet the Intel VR11 Specifications.
The demo board for the NCP5391 is available by request.
It is configured as a three phase solution with decoupling
designed to provide a 1.0 m load line under a 50 A step
load. A schematic is available upon request from ON
Semiconductor.
Startup Procedure
The demo board comes with a Socket 775 and requires
an Intel dynamic load tool (VTT Tool) available through a
third party supplier, Cascade Systems. The web page is
http://www.cascadesystems.net/.
Start by installing the test tool software. It's best to power
the test tool from a separate ATX power supply. The test
tool should be set to a valid VID code of 0.5 V or above
in-order for the controller to start. Consult the VTT help
manual for more detailed instructions.
Startup Sequence
1. Make sure the VTT software is installed.
2. Powerup the PC or Laptop do not start the VTT
software.
3. Insert the VTT Test Tool adapter into the socket
and lock it down.
4. Insert the socket saver pin field into the bottom of
the VTT test tool.
5. Carefully line up the tool with the socket in the
board and press tool into the board.
6. Connect the scope probe, or DMM to the voltage
sense lines on the test tool. When using a scope
probe it is best to isolate the scope from the AC
ground. Make the ground connection on the scope
probe as short as possible.
7. Connect the first ATX supply to the VTT tool.
8. Powerup the first ATX supply to the VTT tool.
9. Start the VTT tool software in VR11 mode with
the current limit set to 150 A.
10. Using the VTT tool software, select a VID code
that is 0.5 V or above.
11. Connect the second ATX supply to the demo
board.
12. Set the VID DIP switches. All the VID switches
should be up or open.
13. Set the VR_ENABLE DIP switch down or
closed.
14. Start the second ATX supply by turning it on and
setting the PSON DIP switch low. The green VID
lights should light up to match the VTT tool VID
setting.
15. Set the VR_ENABLE DIP switch up to start the
NCP5391.
16. Check that the output voltage is about 19 mV
below the VID setting.
Step Load Testing
The VTT tool is used to generate the high di/dt step load.
Select the dynamic loading option in the VTT test tool
software. Set the desired step load size, frequency, duty,
and slew rate. See Figures 8 and 9.
Figure 8. Typical Step Load Response
V
OUT
Load Current
Figure 9. Typical Load Release Event
V
OUT
Load Current
NCP5391
http://onsemi.com
20
Dynamic VID Testing
The VTT tool provides for VID stepping based on the
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.
Figure 10. 1.6 to 0.5 Dynamic VID Response
Figure 11. Dynamic VID Settling Time Rising
Figure 12. Dynamic VID Settling Time Falling
Design Methodology
Decoupling the V
CC
Pin on the IC
An RC input filter is required as shown in the V
CC
pin to
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
The controller will ramp to the 1.1 V, with a pause to
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 A current.
The typical value to use for the soft-start cap (SS), is
typically set to 0.01 F. This results in a ramp time to 1.1 V
of 2.2 ms based on equation 1.
C
ss
^ i
ss
dt
ss
dv
ss
(eq. 1)
1.1·V
2.2·ms
+
dv
ss
dt
ss
and i
ss
+ 5·A
C
ss
+ 0.01·F
Figure 13. VR11 Startup
NCP5391
http://onsemi.com
21
Programming the Current Limit and the Oscillator
Frequency
The demo board is set for an operating frequency of
approximately 300 kHz. The OSC pin provides a 2.0 V
reference voltage which is divided down with a resistor
divider and fed into the current limit pin ILIM. Calculate
the total series resistance to set the frequency and then
calculate the individual values for current limit divider.
The series resistors RLIM1 and RLIM2 sink current to
ground. This current is internally mirrored into a capacitor
to create an oscillator. The period is proportional to the
resistance and frequency is inversely proportional to the
resistance. The resistance may be estimated by equation 2.
This equation is valid for the individual phase frequency in
both three and four phase mode.
ROSC +
10.14 10
9
Frequency
* 1440
(eq. 2)
32.36k ^
10.14 10
9
300·k
* 1440
2 Phase Mode
ROSC +
9.711 10
9
Frequency
* 1111
(eq. 3)
3 Phase Mode
Figure 14. R
OSC
vs. 2-Phase Mode
F
OSC
(kHz)
R
OSC
(k)
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
F
OSC
(2, Calculated)
F
OSC
(2, Measured)
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
F
OSC
(2, Measured)
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
F
OSC
(3, Measured)
F
OSC
(3, Calculated)
Figure 15. R
OSC
vs. 3-Phase Mode
F
OSC
(kHz)
R
OSC
(k)
The current limit function is based on the total sensed
current of all phases multiplied by a gain of 5.94. DCR
sensed inductor current is function of the winding
temperature. The best approach is to set the maximum
current limit based on the expected average maximum
temperature of the inductor windings.
DCR
Tmax
+ DCR
25C
·
(eq. 4)
(1 ) 0.00393·C
-1
(T
Tmax
- 25·C))
Calculate the current limit voltage:
V
ILIMIT
^ 5.94·
ǒ
I
MIN_OCP
·DCR
Tmax
)
DCR
50C
·Vout
2·Vin·F
s
·
ǒ
Vin- Vout
L
* (N- 1)·
Vout
L
ǓǓ
* 0.02
(eq. 5)
Solve for the individual resistors:
(eq. 6)
RLIM2 +
V
ILIMIT
·R
OSC
2·V
RLIM1 + R
OSC
-R
LIM2
Final Equation for the Current Limit Threshold
I
LIMIT
(T
inductor
) ^
ǒ
2·V·RLIM2
RLIM1)RLIM2
Ǔ
) 0.02
5.94·(DCR
25C
·(1 ) 0.00393·C
-1
(T
Inductor
- 25·C)))
*
Vout
2·Vin·F
s
·
ǒ
Vin- Vout
L
* (N- 1)·
Vout
L
Ǔ
(eq. 7)
The inductors on the demo board have a DCR at 25°C of
0.75 m. Selecting the closest available values of 16.9 k
for RLIM1 and 15.8 k for RLIM2 yield a nominal
operating frequency of 305 kHz and an approximate
current limit of 180 A at 100°C. The total sensed current
can be observed as a scaled voltage at the VDRP pin added
to a positive, no-load offset of approximately 1.3 V.
Inductor Selection
When using inductor current sensing it is recommended
that the inductor does not saturate by more than 10% at
maximum load. The inductor also must not go into hard
saturation before current limit trips. The demo board includes
a four phase output filter using the T50- 8 core from
Micrometals with 4turns and a DCR target of 0.75 m @
25°C. Smaller DCR values can be used, however, current
sharing accuracy and droop accuracy decrease as DCR
decreases. Use the excel spreadsheet for regulation accuracy
calculations for a specific value of DCR.
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NCP5391MNR2G

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Buy NCP5391MNR2G
Manufacturer:
ON Semiconductor
Description:
IC REG CTRLR INTEL 3OUT 32QFN
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