NX2415 データシートの表示（PDF） - Microsemi Corporation
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NX2415
Microsemi Corporation
NX2415 Datasheet PDF : 21 Pages
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NX2415
C2
=
1
π × Rcc
× FS
=
1
π × 430Ω × 400kHz
= 1.85nF
Select C2=2.2nF.
VREF
100k
OCP
Frequency Selection
The frequency can be set by external Rt resistor.
The relationship between frequency per phase and RT
pin is shown as follows.
RT
≈
18600000
FS
...(20)
FREQUENCY(kHz) vs RT(kohm )
800
700
600
500
400
300
200
100
0
0
50
100
150
200
Rt(kohm )
ROCP
Figure 12 - Over current protection
Output Voltage Droop Operation
The effective output impedance of the controller must
be adjusted to maximize the output voltage fluctuation
range. A program resistor attached to the Droop pin
RDROOP will program this value. The function works by an
internal current source connected to the FB pin. This
current flows output of the FB pin and through the Rin
resistance from the FB pin to the output.
This current source is a function of the sensed
output current. As the output current increases, the droop
current will increase and causes the output voltage
todroop proportionately. The droop current is programmed
by a resistor attached to the Droop pin. The value of the
resistor is chosen as follows.
Figure 11 - Frequency vs Rt chart
Over Current/Short Circuit Protection
The converter will go into hiccup mode if the
output current reaches a programmed limit VOCP
determined by the voltage at pin OCP.
VOCP
=
0.6 60kΩ
2kΩ +RS
DCR
2 IOCP
ROCP
=
VOCP
VREF − VOCP
× 100kΩ
...(21)
Where Iocp is the desired over current protection
level,100kΩ is the resistor connecting VREF pin and
IOCP pin. RS is the current sensing matching resistor
when using DCR sensing method.
Rev.4.8
05/06/08
VOUT
RIN
FB
IDROOP
COMP
VP
Error Amplifer
Figure 13 - Output voltage droop funciton
∆VOUT = IDROOP × RIN = ∆ILOAD × RLL
...(22)
Where R is desired load impedance. For example,
LL
if we want Vout droops 60mV @ 20A,
RLL
=
60mV
20A
=
3mΩ
IDROOP
=
V(IOUT)
RDROOP
=
0.6 ×
60kΩ
2kΩ + RS
×
DCR
2
× ILOAD
RDROOP
...(23)
16
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