NCP1216AD100 ONSEMI [ON Semiconductor], NCP1216AD100 Datasheet - Page 14

• Manufacturer Part Number: NCP1216AD100
• Description: PWM Current-Mode Controller for High-Power Universal Off-Line Supplies
• Manufacturer: ONSEMI [ON Semiconductor]

the MOSFET drive, establishes at 2.9 mA, we can calculate
the required capacitor using the following formula:
with DV = 2.2 V. Then for a wanted Dt of 30 ms, C equals
39.5 mF or a 68 mF for a standard value (including 20%
dispersions). When an overload condition occurs, the IC
blocks its internal circuitry and its consumption drops to
350 mA typical. This happens at V
stuck until V
Again, using the selected 68 mF and 350 mA current
consumption, this latchoff phase lasts: 780 ms.
Protecting the Controller Against Negative Spikes
is the designer’s duty to avoid the presence of negative
spikes on sensitive pins. Negative signals have the bad habit
to forward bias the controller substrate and induce erratic
behaviors. Sometimes, the injection can be so strong that
internal parasitic SCR activation. One of them consists in
inserting a resistor in series with the high−voltage pin to
keep the negative current to the lowest when the bulk
becomes negative (Figure 27). Please note that the negative
spike is clamped to (−2 * V
the power dissipation of this resistor is extremely small since
it only heats up during the startup sequence.
Dt + DV·C
As with any controller built upon a CMOS technology, it
Simple and inexpensive cures exist to prevent from
i
Figure 26. A Negative Spike Takes Place on the Bulk Capacitor at the Switch−off Sequence
CC
reaches 5.6 V: we are in latchoff phase.
f
0
) due to the diode bridge. Also,
CC
V
5 V/DIV
10 ms/DIV
= 10 V and it remains
CC
NCP1216, NCP1216A
(eq. 19)
http://onsemi.com
14
internal parasitic SCRs are triggered, engendering
irremediable damages to the IC if a low impedance path is
offered between V
often the seat of such spurious signals, the high−voltage pin
can also be the source of problems in certain circumstances.
During the turn−off sequence, e.g. when the user unplugs the
power supply, the controller is still fed by its V
and keeps activating the MOSFET ON and OFF with a peak
current limited by R
coefficient Q of the resonating network formed by L
C
conditions are met to make the circuit resonate and thus
negatively bias the controller. Since we are talking about ms
pulses, the amount of injected charge, (Q = I * t),
immediately latches the controller that brutally discharges
its V
its stored energy damages the controller. Figure 26 depicts
a typical negative shot occurring on the HV pin where the
brutal V
from V
VCC
the bulk capacitor gets deeply discharged. For security
reasons, two diodes can be connected in series.
bulk
Another option (Figure 28) consists in wiring a diode
CC
ON
is low (e.g. the MOSFET R
capacitor. If this V
CC
CC
sooner and thus stops the switching activity before
discharge testifies for latchup.
to the bulk capacitor to force V
V
1 V/DIV
latch
CC
and GND. If the current sense pin is
sense
CC
. Unfortunately, if the quality
capacitor is of sufficient value,
dson
+ R
sense
CC
CC
are small),
capacitor
to reach
p
and