VJ1206Y224KXXAT ONSEMI [ON Semiconductor], VJ1206Y224KXXAT Datasheet - Page 5

• Manufacturer Part Number: VJ1206Y224KXXAT
• Description: Low-Cost 100 mA High-Voltage Buck and Buck-Boost Using NCP1052
• Manufacturer: ONSEMI [ON Semiconductor]

small, the di/dt becomes too high and the NCP1052 will
have a very high current limit effectively because there is a
propagation delay (typically 135 ns) to turn off the switch.
parts. First, there is a V
It happens when V
mA. It is noted that the V
flow through the inductor. Second, it is the main inductor
current to deliver the output current. It is noted that the peak
of burst-mode inductor current is higher than PWM one as
in Figure 5 for the same level of averaged inductor current
(or output current). Finally, there is a current flowing
through diode D
inductor as shown in Figure 3. Its magnitude is a
greater-than-50
Hence, the saturation current of the inductor L is needed to
be bigger than their sum.
filtering capability for the V
(and the 50/ 60 Hz rectified AC line voltage ripple). As
shown in Figure 2, there is a low-frequency charging current
with magnitude 6.3 mA flowing through the inductor and
causes low-frequency ripple in the output voltage. A higher
value of the inductance can help to reduce the output ripple.
It is noted that when the output power is higher, the startup
time becomes longer. It needs bigger V
makes lower V
inductance is needed.
Large inductor can limit the inrush current flowing into
capacitor C
desirable because it can make the C
output voltage. It makes load regulation poor. If there is no
pull-up resistor R
as possible, say 2 mH.
Output Capacitor
low-frequency V
larger than those in PWM. Hence, a relatively bigger output
capacitor is needed to keep output ripple small. However,
big output capacitor needs a long time to build up the output
voltage initially and hence the circuit may enter into fault
mode in the startup in Figure 6.
The current flowing through the inductor L includes three
Another consideration on the inductor is the low-pass
The last consideration is the effect of load regulation.
Because of the burst-mode characteristic and the
1
as shown in Figure 3. High inrush current is not
CC
1
1
CC
to charge up C
A current and practically it is about 1 mA.
charging frequency. As a result, a bigger
, inductor value L is chosen to be as large
CC
charging current, the output ripple is
needs charging. Its magnitude is 6.3
CC
charging current I
CC
CC
discharging current does not
1
hysteresis low frequency
. It also flows through the
1
voltage higher than the
CC
start
capacitor and
in Figure 2.
http://onsemi.com
AND8098/D
5
Buffering Capacitor
to the feedback pin of NCP1052. It is relatively much
smaller than the output capacitor because the current
consumption in this capacitor is much smaller and the output
voltage cannot copy to this buffering capacitor if the
buffering capacitor voltage is higher than the output voltage.
Diodes
compatibility in speed and voltage drop. It helps the voltage
in the capacitor C
reverse blocking voltage of D and D
enough to withstand the input voltage in buck and input
voltage plus output voltage in buck-boost respectively.
that feedback current is only in one direction. The accuracy
of its voltage drop used in (1) is not important since the 4.3V
reference voltage in the NCP1052 is loosely set.
Zener Diodes
or no load. Hence, the accuracy of Z
accuracy in the light load or no load condition. It is also the
main component to consume energy when the circuit is in no
load condition. The output voltage is clamped and hence the
output capacitor is protected.
current. Hence, their accuracy affects the regulation
accuracy at the nominal load condition. The relationship
between zener voltage and output voltage is shown in (1).
Higher value of R
by reducing the charging rate of the buffering capacitor C
Standby Condition
good. It is because there is a V
through the output capacitor in Figure 2(a). This charging
current is a low-frequency pulsating signal. As a result, the
voltage in the output capacitor continuously rises up by the
charging current pulses. In order to prevent over voltage in
the output capacitor, the zener Z
current. It consumes main portion of energy in standby.
Buffering capacitor C
D and D
D
Z
Z
The standby ability of the proposed buck converter is not
1
2
2
and R
is to clamp the output voltage when there is light load
is not a critical component. Its function is to make sure
1
1
are to set the output voltage at the nominal load
are recommended to be the same part for
1
1
helps to pull up the output voltage higher
to be similar to the output voltage. The
2
is to provide a greater-than-50 A
CC
charging current I
1
1
absorbs the charging
1
is needed to be large
helps the regulation
start
flows
1
.