MC34067DWR2G ON Semiconductor, MC34067DWR2G Datasheet - Page 11

• Manufacturer Part Number: MC34067DWR2G
• Description: IC CTRLR SMPS DBL END HF 16-SOIC
• Manufacturer: ON Semiconductor
• Type: Flybackr

Specifications of MC34067DWR2G

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 100mA
• Frequency - Switching: 525kHz ~ 2.05MHz
• Voltage - Input: 2.5 ~ 20 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Power - Output: 862mW
• Output Voltage Range: 5 V to 5.2 V
• Input Voltage Range: 20 V
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

switching
applications. The IC is optimized for double−ended
push−pull or bridge type converters operating in continuous
conduction mode. Operation of this type of ZVS with
resonant properties is similar to standard push−pull or bridge
circuits in that the energy is transferred during the transistor
on−time. The difference is that a series resonant tank is
usually introduced to shape the voltage across the power
transistor prior to turn−on. The resonant tank in this
topology is not used to deliver energy to the output as is the
case with zero current switch topologies. When the power
transistor is enabled the voltage across it should already be
zero, yielding minimal switching loss. Figure 21 shows a
timing diagram for a half−bridge ZVS QRC. An application
circuit is shown in Figure 22. The circuit built is a dc to dc
half−bridge converter delivering 75 W to the output from a
48 V source.
objective is to waveshape the power transistor’s voltage
waveform so that the voltage across the transistor is zero
when the device is turned on. The purpose of the control IC
is to allow a resonant tank to waveshape the voltage across
the power transistor while still maintaining regulation. This
is accomplished by maintaining a fixed deadtime and by
varying the frequency; thus the effective duty cycle is
changed.
the application circuit, the elements that make the resonant
tank are the primary leakage inductance of the transformer
(L
MOSFET (C
C
Soft-Start
The MC34067 is specifically designed for zero voltage
When building a zero voltage switch (ZVS) circuit, the
Primary side resonance can be used with ZVS circuits. In
L
) and the average output capacitance (C
11
Error Amp
Figure 20. Fault Detector and Soft−Start
Clamp
Soft-Start
Buffer
(ZVS)
R
).
9.0 mA
UVLO + Fault
quasi−resonant
6
UVLO
Ground
Latch
Q
Fault
R
S
converter
Fault
OSS
APPLICATIONS INFORMATION
Comparator
1.0 V
Fault
) of a power
(QRC)
http://onsemi.com
10
Fault
Input
11
Soft−Start Circuit
variable frequency Oscillator to start at the maximum
frequency and ramp downward until regulated by the
feedback control loop. The external capacitor at the
C
UVLO+Fault signal. The low voltage on the capacitor
passes through the Soft−Start Buffer to hold the Error
Amplifier output low. After UVLO+Fault switches to a
logic zero, the soft−start capacitor is charged by a 9.0 mA
current source. The buffer allows the Error Amplifier output
to follow the soft−start capacitor until it is regulated by the
Error Amplifier inputs. The soft−start function is generally
applicable to controllers operating below resonance and can
be disabled by simply opening the C
is calculated by Equation 6:
the value of C
the C
value of the C
MOSFET. For the application circuit the average C
be calculated by Equation 7:
achieve the desired resonant frequency.
than the leakage inductance. Figure 21 shows the primary
current ramping toward its peak value during the resonant
transition. During this time, there is circulating current
flowing through the secondary inductance, which
effectively makes the primary inductance appear shorted.
Therefore, the current through the primary will ramp to its
peak value at a rate controlled by the leakage inductance and
the applied voltage. Energy is not transferred to the
secondary during this stage, because the primary current has
not overcome the circulating current in the secondary. The
larger the leakage inductance, the longer it takes for the
primary current to slew. The practical effect of this is to
lower the duty cycle, thus reducing the operating range.
Soft−Start
The Soft−Start circuit shown in Figure 20 forces the
The desired resonant frequency for the application circuit
In the application circuit, the operating voltage is low and
The MOSFET chosen fixes C
However, the desired resonant frequency is less critical
OSS
C R
of a MOSFET changes with drain voltage, the
terminal is initially discharged by the
=
R
OSS
is approximated as the average C
versus Drain Voltage is known. Because
2 * C OSS
ƒ r
=
2
π
measured at
L L 2C R
1
R
and that L
Soft−Start
1
2
L
terminal.
is adjusted to
V
in
OSS
OSS
(eq. 6)
(eq. 7)
of the
can