ncv8871 ON Semiconductor, ncv8871 Datasheet - Page 10

• Manufacturer Part Number: ncv8871
• Description: Ncv8871 Automotive Grade Non-synchronous Boost Controller
• Manufacturer: ON Semiconductor

as follows:
4. Select Output Capacitors
reduce the overshoot and undershoot associated with line
transients. The steady state output ripple associated with the
output capacitors can be calculated as follows:
follows:
encouraged to help with the transient response.
5. Select Input Capacitors
the module associated with the ac component of the input
current.
6. Select Feedback Resistors
output of the converter to ground, with a tap to the feedback
pin. During regulation, the divided voltage will equal V
The lower feedback resistor can be chosen, and the upper
feedback resistor value is calculated as follows:
V
OUT(ripple)
The maximum average inductor current can be calculated
The Peak Inductor current can be calculated as follows:
The output capacitors smooth the output voltage and
The capacitors need to survive an RMS ripple current as
The use of parallel ceramic bypass capacitors is strongly
The input capacitor reduces voltage ripple on the input to
The feedback resistors form a resistor divider from the
Where: I
I
L,peak
I
OUT(max)
I
+ I
Cout(RMS)
+
L,peak
L,avg
R
I
upper
Cin(RMS)
V
C
I
L,avg
: Peak inductor current value [A]
OUT
OUT
)
+ I
+ R
V
f
+
* V
IN(min)
OUT
2
+
Lf
V
lower
s
OUT
IN(min)
V
V
Lf
V
IN(WC)
OUT
2
s
IN(min)
D
I
V
V
V
OUT(max)
max
out
OUT
OUT
)
V
2
V
* V
ref
2 3
D
* V
I
IN(min)
OUT(max)
WC
ref
IN(min)
V
IN(min)
V
OUT
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R
ESR
ref
.
10
The total feedback resistance (R
the range of 1 kW – 100 kW.
7. Select Compensator Components
allows the use of a simple, Type II compensation to optimize
the dynamic response according to system requirements.
8. Select MOSFET(s)
the MOSFET(s) chosen must not violate the following
inequality:
maximum output voltage, which is the higher of the
maximum input voltage and the regulated output voltaged:
9. Select Diode
current through diode will be equal to the output current:
higher of the output voltage and the maximum input voltage:
calculated as follows:
Current Mode control method employed by the NCV8871
In order to ensure the gate drive voltage does not drop out
The maximum RMS Current can be calculated as follows:
The maximum voltage across the MOSFET will be the
The output diode rectifies the output current. The average
Additionally, the diode must block voltage equal to the
The maximum power dissipation in the diode can be
Where: P
Where: Q
V
f(max)
I
f
drv
s
d
: Switching Frequency [Hz]
: Power dissipation in the diode [W]
: Drive voltage current [A]
g(total)
: Maximum forward voltage of the diode [V]
P
V
V
D
: Total Gate Charge of MOSFET(s) [C]
I
Q(max)
D(max)
D(avg)
I
+ V
D(max)
Q
g(total)
f (max)
+ I
+ V
+ V
+ I
v
OUT(max)
OUT(max)
OUT(max)
I
out
upper
OUT(max)
I
drv
f
s
D
D
+ R
lower
) should be in