NCP1560_06 ONSEMI [ON Semiconductor], NCP1560_06 Datasheet - Page 14

• Manufacturer Part Number: NCP1560_06
• Description: Full Featured Voltage Mode PWM Controller
• Manufacturer: ONSEMI [ON Semiconductor]

reaches 11 V, the controller initiates a soft−start cycle.
Figure 31 shows the relationship between the UV/OV
voltage, the outputs and the soft−start voltage.
Feedforward Ramp Generator
compensate for changes in line voltage. A FF Ramp
proportional to V
line voltage changes, the FF Ramp slope changes
accordingly. The duty cycle will be adjusted immediately
instead of waiting for the line voltage change to propagate
around the system and be reflected back on V
feedforward current (I
charging an internal 10 pF capacitor (C
current proportional to I
(capacitor is discharged) once the Oscillator Ramp reaches
2.0 V. Please refer to Figure 2 for a functional drawing of the
Feedforward Ramp generator.
operating frequency and the required duty cycle. If the
operating frequency and maximum duty cycle are known,
I
where V
Max DC Comparator and t
FF
Once the UV or OV condition is removed and V
The NCP1560 incorporates line feedforward (FF) to
A resistor between V
I
FF
is calculated using the equation below:
is usually a few hundred mA, depending on the
DC(inv)
V
V
AUX(on)
AUX(off)
OUT2
OUT1
V
I FF +
AUX
0 V
2 V
0 V
0 V
0 V
0 V
is the voltage on the inverting input of the
in
C FF
is generated and compared to V
Soft−Start Voltage
UV/OV Voltage
FF
6.7 kW
in
). The FF Ramp is generated by
on(max)
FF
V DC(inv)
and the FF pin (R
Figure 31. Soft−Start Timing Diagram (Using Auxiliary Winding)
. The FF Ramp is finished
t on(max)
is the maximum ON time.
125 kW
FF
) with a constant
EA
FF
.
) sets the
EA
http://onsemi.com
. If the
AUX
14
enable/disable function. Biasing the UV/OV pin below its
UV threshold disables the converter.
Figure 18 shows the relationship between I
For example, if a system is designed to operate at 300 kHz,
with a 60% maximum duty cycle at 36 V, the DC
be grounded and I
feedforward resistor is calculated using the equation below:
controlled predominantly by the value of R
resistance seen into the FF pin is only 12 kW. If a tight
maximum duty cycle control over temperature is required,
R
R FF +
FF
The UV/OV pin can also be used to implement a remote
As the minimum line voltage is 36 V, the required
From the above calculations it can be observed that I
t on(max) + DC MAX
should have a low thermal coefficient.
I FF +
I FF
V in
T + 1
+
* 12.0 kW + 36 V
SOFT−START
C FF
10 pF
f
+
FF
6.7 kW
300 kHz
is calculated as follows:
6.7 kW
V DC(inv)
1
0.888 V
T + 0.6
82.8 mA
+ 3.33 ms
t on(max)
2.0 ms
* 12.0 kW [ 434 kW
125 kW
125 kW
3.33 ms + 2.0 ms
FF
+ 82.8 mA
and DC
MAX
FF
, as the
pin can
MAX
FF
is
.