AN8014 Panasonic Semiconductor, AN8014 Datasheet - Page 10

• Manufacturer Part Number: AN8014
• Description: Step-down/ step-up/ or inverting DC-DC converter control IC
• Manufacturer: Panasonic Semiconductor

AN8014S
10
[1] Function descriptions (continued)
6. Remote circuit
7. PWM comparator block
Application Notes (continued)
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 A 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.
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.
connecting the DTC and GND pins through the external resistor R
100% at V
triangular wave vary with the oscillator frequency.
Example) When f
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.
are gradually widened, the AN8014S will be in soft-start operation. Thus the overshoot at the output of DC-DC
converters can be prevented.
CT waveform
DTC
waveform
Out waveform
It is possible to switch on or off the IC control by using an external control signal. When the OFF pin (pin 16)
The PWM comparator controls the on-period of output pulse in accordance with the input voltage. While the
The dead-time is set by adjusting the voltage V
The DTC pin has constant current output determined by the resistor R
When the oscillator frequency f
The levels of overshooting and undershooting of the peak value V
Output duty ratio Du and DTC pin voltage V
There may be an operational delay of the PWM comparator and a difference in peak and trough values of the
In starting, if the capacitor C
Du
I
V
DTC
DTC
V
Therefore, the following are obtained.
I
V
Du
DTC
DTC
t
ON
CTH
DTC
V
I
R
DTC
RT
of 1.32 V typical.
t
T
ON
52.3 [%]
is approximately 1.32 V, V
t
13.3 [ A]
OSC
OFF
0.99 [V]
R
1
2
DTC
t
Off
OFF
215 [kHz] (R
100 [%]
[A]
V
RT
t
On
ON
DTC
R
OSC
Figure 4. Setting the dead-time
(V
R
DTC
V
is added in parallel to the external resistor R
T
T
DTC
CTH
is 200 kHz, the output duty cycle will be 0% at V
Off
15 k , C
1
2
CTH
V
V
CTL
CTL
[V]
is approximately 0.44 V, and V
DTC
)
T
DTC
1.1
1.1
are expressed by the following formulas;
120 pF) and R
V
V
V
on the DTC pin (pin 5) as shown in figure 4.
CTH
DTC
CTL
100 [%]
DTC
DTC
.
CTH
V
I
DTC
R
75 [k ]
REF
DTC
DTC
T
and the trough value V
. Therefore V
RT
DTC
is approximately 0.4 V.
, and the output pulse width
Voltage regulators
DTC
C
CT
FB
DTC
of 0.44 V typical and
DTC
is adjusted by
PWM
CTL
of the