NCP1200AP40G ON Semiconductor, NCP1200AP40G Datasheet - Page 12

• Manufacturer Part Number: NCP1200AP40G
• Description: IC CTRLR PWM CM HV 8DIP
• Manufacturer: ON Semiconductor

Specifications of NCP1200AP40G

• Output Isolation: Isolated
• Frequency Range: 37 ~ 48kHz
• Voltage - Input: 12.1 ~ 16 V
• Operating Temperature: 0°C ~ 150°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: NCP1200AP40GOS

Protecting the Controller Against Negative Spikes and
Turn−off Problems
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 SCRs are triggered, engendering
irremediable damages to the IC if they are a low impedance
path is offered between V
pin is 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
show an abnormal behavior and can stay high a few tens of
milliseconds. This problem can occur at turn−off but is
usually harmless since the bulk capacitor has been
discharged by the switching pulses. However, the problem
As with any controller built upon a CMOS technology, it
In low V
CC
Figure 22. A negative spike takes place on the Bulk capacitor at the switch−off sequence
conditions, the NCP1200A gate drive signal
Figure 23. If quick V
CC
and GND. If the current sense
VFB
V
CC
CC
depletion is lacking, the drive output can remain high.
Vbulk = 0
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fed by its V
ON and OFF with a peak current limited by Rsense.
Unfortunately, if the quality coefficient Q of the resonating
network formed by Lp and Cbulk is low (e.g. the MOSFET
Rdson + Rsense are small), 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 x t) immediately latches the controller which
brutally discharges its V
is of sufficient value, its stored energy damages the
controller. Figure 22 depicts a typical negative shot
occurring on the HV pin where the brutal V
testifies for latchup.
can become worse if high V
Be sure that the selected MOSFET V
(minimum) and 4.0 V (maximum). Figure 23 shows the
typical operating waveforms.
Vgs
CC
capacitor and keeps activating the MOSFET
CC
capacitor. If this V
T
MOSFETs are implemented.
T
is between 2.0 V
CC
CC
discharge
capacitor