NCP1216AD100 ONSEMI [ON Semiconductor], NCP1216AD100 Datasheet - Page 11

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

the nominal switching frequency whose sweep is
synchronized with the V
peak−to−peak ripple, the NCP1216P065 frequency will
equal 65 kHz in the middle of the ripple and will increase as
V
portrays the behavior we have adopted:
Skipping Cycle Mode
the output power demand drops below a given level. This is
accomplished by monitoring the FB pin. In normal
operation, pin 2 imposes a peak current accordingly to the
load value. If the load demand decreases, the internal loop
asks for less peak current. When this setpoint reaches a
determined level, the IC prevents the current from
decreasing further down and starts to blank the output
pulses: the IC enters the so−called skip cycle mode, also
named controlled burst operation. The power transfer now
depends upon the width of the pulse bunches (Figure 22).
Suppose we have the following component values:
L
F
I
10 ms over a recurrent period of 100 ms, then the total power
transfer is:
p
sw
p
1
2
4
CC
The NCP1216 automatically skips switching cycles when
The theoretical power transfer is therefore:
If this IC enters skip cycle mode with a bunch length of
skip = 600 mA (or 333 mV / R
, primary inductance = 350 mH
, switching frequency = 65 kHz
Frequency Jittering on the Internal Oscillator
rises or decrease as V
Figure 20. V
L p
0.1 + 400 mW.
VCC
62 kHz
I p 2
ON
V
CC
Ripple
F sw + 4 W.
CC
VCC
Ripple is Used to Introduce a
65 kHz
OFF
CC
Sawtooth
ripple. For instance, with a 2.2 V
CC
sense
ramps down. Figure 20
68 kHz
)
NCP1216, NCP1216A
http://onsemi.com
(eq. 8)
(eq. 9)
11
a look at the operation mode versus the FB level
immediately gives the necessary insight:
default), the peak current cannot exceed 1.0 V/R
the IC enters the skip cycle mode, the peak current cannot go
below V
1.0 V by either shunting pin 1 to ground through a resistor
or raising it through a resistor up to the desired level.
Grounding pin 1 permanently invalidates the skip cycle
operation.
FB
To better understand how this skip cycle mode takes place,
When FB is above the skip cycle threshold (1.0 V by
Figure 22. Output Pulses at Various Power Levels
Normal Current Mode Operation
I
pin1
pMIN
Skip Cycle Operation
/ 3.3. The user still has the flexibility to alter this
= 333 mV / R
(X = 5 ms/div) P1 < P2 < P3
Figure 21.
sense
Power P1
4.2 V, F
3.2 V, Upper
Dynamic Range
1 V
B
sense
Pin Open
Power
Power
. When
P2
P3