AN8014 データシートの表示（PDF） - Panasonic Corporation
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AN8014 Datasheet PDF : 18 Pages
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AN8014S
Voltage regulators
s Application Notes (continued)
[1] Function descriptions (continued)
6. Remote circuit
It is possible to switch on or off the IC control by using an external control signal. When the OFF pin (pin 16)
voltage is lowered to below approximately 0.8 V, the internal reference voltage goes down thereby stopping the
IC control and reducing the circuit current to 5 µA or less. When the OFF pin voltage is increased to approximately
2.0 V or more, the internal reference voltage rises thereby starting the control operation.
7. PWM comparator block
The PWM comparator controls the on-period of output pulse in accordance with the input voltage. While the
triangular wave voltage on the CT pin (pin 3) is lower than both the error amplifier's output voltage on pin 8 and
the voltage on the DTC pin (pin 4), the output on the Out pin (pin 13) will be set to high level. Then the switching
element (n-channel MOSFET) will be turned on.
The dead-time is set by adjusting the voltage VDTC on the DTC pin (pin 5) as shown in figure 4.
The DTC pin has constant current output determined by the resistor RT . Therefore VDTC is adjusted by
connecting the DTC and GND pins through the external resistor RDTC .
When the oscillator frequency fOSC is 200 kHz, the output duty cycle will be 0% at VDTC of 0.44 V typical and
100% at VDTC of 1.32 V typical.
The levels of overshooting and undershooting of the peak value VCTH and the trough value VCTL of the
triangular wave vary with the oscillator frequency.
CT waveform
DTC
waveform
tOFF
tON
Out waveform
Off On Off
VCTH
VDTC
VCTL
VREF
IDTC
DTC
RDTC
CT
PWM
FB
CDTC
Figure 4. Setting the dead-time
Output duty ratio Du and DTC pin voltage VDTC are expressed by the following formulas;
Du =
tON
tON − tOFF
×
100 [%] =
VDTC − VCTL × 1.1
(VCTH − VCTL) × 1.1
× 100
[%]
IDTC =
VRT
RT
×
1
2
[A]
VDTC
=
IDTC
×
RDTC
=
VRT
×
RDTC
RT
×
1
2
[V]
Example) When fOSC = 215 [kHz] (RT = 15 kΩ, CT = 120 pF) and RDTC = 75 [kΩ]
VCTH is approximately 1.32 V, VCTH is approximately 0.44 V, and VRT is approximately 0.4 V.
Therefore, the following are obtained.
IDTC ≈ 13.3 [µA]
VDTC ≈ 0.99 [V]
Du ≈ 52.3 [%]
There may be an operational delay of the PWM comparator and a difference in peak and trough values of the
triangular wave oscillation. Discrepancies between the values obtained from the above formulas and the actual
values may occur, in which case adjust the values on the mounting substrate.
In starting, if the capacitor CDTC is added in parallel to the external resistor RDTC , and the output pulse width
are gradually widened, the AN8014S will be in soft-start operation. Thus the overshoot at the output of DC-DC
converters can be prevented.
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