an8038 Panasonic Corporation of North America, an8038 Datasheet - Page 12

• Manufacturer Part Number: an8038
• Description: Ac-dc Switching Power Supply Control Ic With Rcc Local Resonance Circuit For Improved Conformance With Energy Conservation Laws
• Manufacturer: Panasonic Corporation of North America

AN8038, AN8038S
12
[2] Operation descriptions (continued)
Out pin voltage
2. Oscillator circuit (continued)
CF pin voltage
Application Notes (continued)
V
a) Normal control - heavy load (I
Allows the
control switching
operating point
to be lowered.
CC
Notes on switching from RCC operation to discontinuous operation
increases along with the increase of the amount of feedback current. Then, when the IFB pin feedback current
exceeds 1 mA (typical) and the VFB voltage becomes larger than the RSTB pin (pin 2) voltage, the minimum off-
period current that is from the CF pin lower limit value until the RSTB pin voltage is reached, is rapidly reduced,
and the operating frequency is lowered. (See figure 3.) This allows the switching loss to be reduced to the mini-
mum, and allows the standby mode power to be reduced.
discontinuous operation, is set by resistor-division of the internal 7 V reference voltage to a typical value of 3.5 V.
This value can be adjusted by connecting an external pull-down resistor, and this can be used to suppress in-
creases of the minimum off-period.
resistors and temperature coefficient of 2 400 ppm/ C.
V
4.2 V
0.2 V
1.5 V
When the state changes from normal load to standby mode, the post-I-V conversion output monitor voltage V
Furthermore, the RSTB pin voltage, which is operating point for switching from RCC operation to
Note that application designs must take into account the sample-to-sample variations of 15% in the internal
RSTB
0 V
0 V
PC
t
OFF(min)
RSTB
t
OFF
IFB
Figure 3. Off-period block diagram and control waveforms
17.5 k
17.5 k
Current mirror
20 k
IFB
On
5 : 1
1 mA)
V
7 V
V
FB
I
FB
OFF
I
OFF
CF pin voltage
Out pin voltage
(I
(I
IFB
IFB
V
1250 A typ.
CC
55 A typ.
1 mA)
1 mA)
V
4.2 V
0.2 V
1.5 V
Comp.
RSTB
0 V
0 V
b) Standby (I
I
C
7 V
OFF
t
CF
OFF(min)
t
OFF
Out
GND
V
CC
IFB
1 mA)
On
E
E
Voltage Regulators
IN
IN
The minimum off-period
current is reduced
when V
t
OFF (min)
V
FB
: large
FB
V
RSTB
N
N
P
B
.
FB