NCP1392B_12 Datasheet, PDF (13/21 Pages) ON Semiconductor – High-Voltage Half-Bridge Driver with Inbuilt Oscillator

NCP1392B, NCP1392D
This is valuable for applications that are supplied from
auxiliary winding and V_CC capacitor is supposed to provide
energy during PFC delay period.
For the resonant applications and light ballast applications
it is necessary to adjust minimum operating frequency with
high accuracy. The designer also needs to limit maximum
operating and startup frequency. All these parameters can be
adjusted using few external components connected to the Rt
pin as depicted in Figure 29.
NCP1392
R_t
R_fstart
R_t
C_SS
R_fmax
(to secondary
voltage regulator)
R_fmax−OCP
D1
V_CC
R_bias
R_comp
C_comp
TLV431
(to primary
current sensor)
Voltage Feedback
Current Feedback
Figure 29. Typical Rt Pin Connection
The minimum switching frequency is given by the Rt
resistor value. This frequency is reached if there is no
optocoupler or current feedback action and soft start period
has been already finished. The maximum switching
frequency excursion is limited by the Rf_max selection. Note
that the F_max value is influenced by the optocoupler
saturation voltage value. Resistor Rfstart together with
capacitor C_SS prepares the soft start period after PFC timer
elapses. The Rt pin is grounded via an internal switch during
the PFC delay period to assure that the soft start capacitor
will be fully discharged via Rfstart resistor.
There is a possibility to connect other control loops (like
current control loop) to the Rt pin. The only one limitation
lies in the Rt pin reference voltage which is Vref_Rt = 3.5 V.
Used regulator has to be capable to work with voltage lower
than Vref_Rt.
The TLV431 shunt regulator is used in the example from
figure 4 to prepare current feedback loop. Diode D1 is used
to enable regulator biasing via resistor Rbias. Total
saturation voltage of this solution is 1.25 + 0.6 = 1.85 V for
room temperature. Shottky diode will further decrease
saturation voltage. Rf_max − OCP resistor value, limits the
maximum frequency that can be pushed by this regulation
loop. This parameter is not temperature stable because of the
D1 temperature drift.
Brown−Out Protection
The Brown−Out circuitry (BO) offers a way to protect the
application from low DC input voltages. Below a given
level, the controller blocks the output pulses, above it, it
authorizes them. The internal circuitry, depicted by
Figure 30, offers a way to observe the high−voltage (HV)
rail.
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