NCP1562B ON Semiconductor, NCP1562B Datasheet - Page 21

• Manufacturer Part Number: NCP1562B
• Description: High Performance Active Clamp/Reset PWM Controller
• Manufacturer: ON Semiconductor

resistor, R
is proportional to R
obtained by grounding the t
trailing delay. This allows the user to optimize the delay for
the turn on transition of the main switch and ensures the
active clamp switch always exhibits zero volt switching.
Analog and Power Ground (PGND)
ground, PGND, terminal. GND is used for analog
connections such as V
others. PGND is used for high current connections such as
the internal output drivers. It is recommended to have
independent analog and power ground planes and connect
them at a single point, preferably at the ground terminal of
the system. This will prevent high current flowing on
PGND from injecting noise in GND. The PGND
connection should be as short and wide as possible to
reduce inductance−induced spikes.
Oscillator
set by an R
A 500 mA current source (I
capacitor (C
(V
equation has two variables and can be solved iteratively. In
general, the time delay is a small portion of the ON time and
can be ignored as a first approximation. R
variation vs R
than 6.0 kW. Otherwise, the R
exceed the pulldown current and the oscillator will be in an
undefined state.
The output overlap delay is adjusted by connecting a
The leading delay is purposely made longer than the
The NCP1562 has an analog ground, GND, and a power
The oscillator frequency and maximum duty cycle are
The duty cycle, D, is given by Equation 7.
It can be observed that D is set by R
Figures 23 through 26 show the frequency and duty cycle
RTCT(peak)
D
T
, from the t
C
), typically 3.0 V. Once C
T
T
T
D +
) upon reaching its peak threshold
for several C
divider from V
t RTCT(C) ) t RTCT(D)
D
D
. A minimum delay of 20 ns is
t RTCT(C) −t D
REF
pin to ground. The overlap delay
D
t RTCT(D) + R T C T
, R
T
RTCT
values. R
pin.
REF
f +
T
T
C
C
) discharges the timing
T
D +
as shown in Figure 48.
R T C T
T
, feedforward among
charge current will
T
T
ln
T
reaches its valley
, C
should not be less
T
V RTCT(valley) −V REF
V RTCT(peak) −V REF
is then selected
T
ln
and t
V RTCT(valley) −V REF
V RTCT(peak) −V REF
ln
ln
D
http://onsemi.com
(eq. 7)
. This
(I RTCT
V RTCT(valley) −V REF
(I RTCT
V RTCT(peak) −V REF
21
(I RTCT R T ))V RTCT(peak) −V REF
(I RTCT )V RTCT(valley) −V REF
1
R T ) ) V RTCT(valley) −V REF
voltage (V
allowing C
waveform on the RTCT pin has a sawtooth like shape.
by OUT1 delayed by the overlap delay. Once V
is reached, OUT1 goes low, followed by OUT2 delayed by
t
overlap delay over the total charge and discharge (t
times. The charge and discharge times are calculated using
Equations 5 and 6. However, these equations are an
approximation as they do not take into account the
propagation delays of the internal comparator.
R T ) ) V RTCT(peak) −V REF
algebraic manipulation and replacing values, it simplifies
to:
to achieve a given duty cycle. Once the R
is chosen to obtain the desired operating frequency using
Equation 9.
Synchronization
architecture allows multiple NCP1562 to synchronize in a
master−slave configuration. It can synchronize to
frequencies above or below the free running frequency.
D
(I RTCT R T ))V RTCT(valley) −V REF
(I RTCT R T ))V RTCT(peak) −V REF
OUT2 is set high once V
.
The duty cycle is the C
Substituting Equations 5, 6, and 7, and after a little
A proprietary bidirectional frequency synchronization
t RTCT(C) + R T C T
−
R T C T
t D
Figure 48. Oscillator Configuration
RTCT(valley)
T
to charge back up through R
Enable
), typically 2.0 V, I
T
ln
I
RTCT
charge time (t
RTCT(valley)
V RTCT(valley) −V REF
V RTCT(peak) −V REF
RTCT
V
REF
C
is reached, followed
R
T
T
RTCT(C)
T
RTCT
T
. The resulting
is selected, C
3 V
2 V
) minus the
turns OFF
RTCT(peak)
RTCT(D)
(eq. 5)
(eq. 9)
(eq. 6)
(eq. 8)
T
)