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參數(shù)資料
| 型號(hào)： | AN8021SB |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | AC-DC switching power supply control IC |
| 中文描述： | 1 A SWITCHING CONTROLLER, 225 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 0.225 INCH, PLASTIC, SSOP-16 |
| 文件頁數(shù)： | 14/16頁 |
| 文件大?。?/td> | 141K |
| 代理商： | AN8021SB |
14
AN8021L, AN8021SB
Voltage Regulators
I
Application Notes (continued)
[2] Operation descriptions (continued)
7. Output Block
The AN8021L and AN8021SB employ the out-
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.
The maximum sink/source current is
±
0.1 A
(DC) and
±
1.0 A (peak). Even when the supply
voltage V
CC
is under the stop voltage, the sink
function works to ensure that the power MOSFET
be turned off.
For the current capability, the peak current is major concern, and the particularly large current is not required
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.
For the AN8021L or AN8021SB, capacitance value of the power MOSFET used is taking into account, and
the capability of peak value
±
1 A is ensured.
The parasitic LC of the power MOSFET may produce ringing which makes the output pin go under the GND
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.
[3] Design reference data
1. Setting the output frequency
The output is controlling the triangular oscillation with PWM control: Triangular oscillation frequency
=
output
frequency
CT (C6)
=
capacitor terminal for triangular oscillation
RT (C7)
=
resistor terminal for triangular oscillation
[Reference calculation formula]
V
OSC
H
T
1
=
T
2
=
C
6
· V
2I
RT
(charge/discharge current)
Since the I
RT
is given by rough calculation of 2.5 V/R
T
, and
V becomes approximately 3 V, the output frequency is obtained
in the following equation:
1
=
T
1
+
T
2
C
6
· V
f
OUT
=
I
RT
=
5
6 · C
6
· R
7
However, it may deviate a little from the design value due to delay of the internal circuit.
(Reference value)
f
OUT
=
approximately 200 kHz
at C
T
(C6)
=
220 pF and R
T
(R7)
=
19 k
Figure 9
Schottky
barrier diode
T
2
T
1
V
OSC
L
V
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