ncp1395 ON Semiconductor, ncp1395 Datasheet - Page 15

• Manufacturer Part Number: ncp1395
• Description: High Performance Resonant Mode Controller
• Manufacturer: ON Semiconductor

•
Voltage−Controlled Oscillator
allowing an internal operation from 100 kHz up to
2.0 MHz. However, as a division by two internally creates
the two Q and Qbar outputs, the final effective signal on
The VCO section features a high−speed circuitry
Finally, Two Circuit Versions, A and B: The A and
B versions differ because of the following changes:
1. The startup thresholds are different, the A starts
to pulse for V
for V
same, however. The A is recommended for
consumer products where the designer can use
an external startup resistor, whereas the B is
Vcc
CC
= 10 V. The turn off levels are the
Rt−m sets
Fmin for V(FB) < Vfb_off
Rdt sets
the deadtime
Rt−max sets
the maximum Fsw
CC
Fmin
DT
Fmax
= 12.8 V whereas the B pulses
FB
Rfb
20 k
Vref
Vref
Figure 33. Simplified VCO Architecture
Vdd
Vdd
Vdd
Imin
Imin
Cint
http://onsemi.com
NCP1395A/B
0 to I_Fmax
IDT
15
output A and B switches between 50 kHz and 1.0 MHz.
The VCO is configured in such a way that if the feedback
pin goes up, the switching frequency also goes up.
Figure 33 shows the architecture of this oscillator.
FBinternal
+
−
+
+
−
2. The A version does not activate the soft−start
more recommended for industrial/medical
applications where a 12 V auxiliary supply
directly powers the chip.
upon release of the fast fault input. This is to let
the designer implement skip cycle. To the
opposite, the B version goes back to operation
upon the fast fault pin release via a soft−start
sequence.
max
max
Fsw
Vb_fault
+
+
−
D
Clk
S
R
Q
Q
Vfb < Vb_fault
start fault timer
A
B