an8021l Panasonic Corporation of North America, an8021l Datasheet - Page 14

• Manufacturer Part Number: an8021l
• Description: Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8021L, AN8021SB
14
[2] Operation descriptions (continued)
[3] Design reference data
7. Output Block
1. Setting the output frequency
Application Notes (continued)
put circuit using the totem pole (push-pull) method,
by which sink/source of current is performed with
the NPN transistor as shown in figure 9, in order to
drive the power MOSFET at high speed.
(DC) and 1.0 A (peak). Even when the supply
voltage V
function works to ensure that the power MOSFET
be turned off.
normally: the power MOSFET which works as load on the output is capacitive load. Therefore, in order to drive
it at high speed, the large peak current is required. However, after charge/discharge, particularly large current is
not required to keep that condition.
the capability of peak value 1 A is ensured.
potential. When the decrease of the output pin becomes larger than the voltage drop of diode and its voltage
becomes negative, the parasitic diode consisting of the substrate and collector of the output NPN turns on. This
phenomenon may cause the malfunction of the device. In such a case, the Schottky barrier diode should be
connected between the output and GND.
frequency
V
V
OSC
OSC
The AN8021L and AN8021SB employ the out-
The maximum sink/source current is 0.1 A
For the current capability, the peak current is major concern, and the particularly large current is not required
For the AN8021L or AN8021SB, capacitance value of the power MOSFET used is taking into account, and
The parasitic LC of the power MOSFET may produce ringing which makes the output pin go under the GND
The output is controlling the triangular oscillation with PWM control: Triangular oscillation frequency output
However, it may deviate a little from the design value due to delay of the internal circuit.
(Reference value)
CT (C6) capacitor terminal for triangular oscillation
RT (C7) resistor terminal for triangular oscillation
f
at C
OUT
H
L
T
CC
(C6)
approximately 200 kHz
is under the stop voltage, the sink
T
220 pF and R
1
T
2
T
(R7)
V
19 k
V becomes approximately 3 V, the output frequency is obtained
in the following equation:
[Reference calculation formula]
Since the I
T
f
OUT
1
T
2
T
RT
1
1
2I
is given by rough calculation of 2.5 V/R
T
RT
2
(charge/discharge current)
C
I
6
RT
C
Figure 9
· V
6
· V
Voltage Regulators
Schottky
barrier diode
6 · C
5
6
· R
7
T
, and