ncp1396 ON Semiconductor, ncp1396 Datasheet - Page 14

• Manufacturer Part Number: ncp1396
• Description: High Performance Resonant Mode Controller With High And Low Sides Drivers
• Manufacturer: ON Semiconductor

frequency and the minimum switching frequency. In LLC
configurations, for circuits working above the resonant
frequency, a high precision is required on the minimum
frequency, hence the ±3% specification. This minimum
switching frequency is actually reached when no feedback
closes the loop. It can happen during the startup sequence,
a strong output transient loading or in a short-circuit
condition. By installing a resistor from pin 4 to GND, the
minimum frequency is set. Using the same philosophy,
The designer needs to program the maximum switching
2. The A version does not activate the soft-start
products where the designer can use an external
startup resistor, whereas the B is 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.
Vcc
Rt sets
Fmin for V(FB) = 0
Rdt sets
the dead-time
Fmax sets
the maximum Fsw
Fmax
DT
Rt
FB
Rfb
20 k
Figure 31. The Simplified VCO Architecture
Vref
Vref
NCP1396A, NCP1396B
Vdd
Vdd
Vdd
http://onsemi.com
Imin
Imin
Cint
0 to I_Fmax
IDT
14
Voltage-Controlled Oscillator
allowing operation from 100 kHz up to 1 MHz. However,
as a division by two internally creates the two Q and Q
outputs, the final effective signal on output Mlower and
Mupper switches between 50 kHz and 500 kHz. The VCO
is configured in such a way that if the feedback pin goes up,
the switching frequency also goes up. Figure 31 shows the
architecture of this oscillator.
wiring a resistor from pin 2 to GND will set the maximum
frequency excursion. To improve the circuit protection
features, we have purposely created a dead zone, where the
feedback loop has no action. This is typically below 1.2 V.
Figure 32 details the arrangement where the internal
voltage (that drives the VCO) varies between 0 and 2.3 V.
However, to create this swing, the feedback pin (to which
the optocoupler emitter connects), will need to swing
typically between 1.2 V and 5.3 V.
The VCO section features a high-speed circuitry
FBinternal
+
-
+
+
-
max
max
Fsw
Vb_off
+
+
-
D
Clk
S
R
Q
Q
Vfb < Vb_off
Start fault timer
A
B