AN8038S Panasonic Semiconductor, AN8038S Datasheet - Page 19

• Manufacturer Part Number: AN8038S
• Description: AC-DC switching power supply control IC with RCC local resonance circuit for improved conformance with energy conservation laws
• Manufacturer: Panasonic Semiconductor

Voltage Regulators
[2] Operation descriptions (continued)
5. Output block (continued)
Application Notes (continued)
Operating power supply current characteristics
voltage V
resistance mode when the OVP circuit operates, and thus the increases of the supply voltage.
supply voltage V
operates is stabilized at a value (note that
this value depends on the value of the
startup resistor) that is larger than the OVP
release voltage (7.5 V typical), the OVP
circuit will not be reset as long as the AC
input is not cut. (See figure 11.) Note that
this does not apply to an external reset.
Overcurrent protection circuit (pulse-by-pulse overcurrent protection)
in the primary side main switch (power MOSFET). This circuit limits overcurrents in the power supply output
by constraining the upper limit of the pulse current flowing in the main switch, and thus protects components
sensitive to excessive current.
source and ground and monitoring the voltage that appears across that resistor. When the power MOSFET is
turned on and the CLM (current limit) threshold voltage is detected, the output is turned off. This controls the
circuit so that a current in excess of that limit cannot flow by turning off the power MOSFET. The CLM
threshold voltage is about 205 mV with respect to ground at T
every cycle, once an overcurrent is detected, the off state is held for the remainder of that cycle, and the circuit
is not turned on until the next period. This type of overcurrent detection is called "pulse-by-pulse overcurrent
detection."
filter circuit that rejects noise gener-
ated due to the incidental equivalent
parasitic capacitance when the
power MOSFET is on.
ommend that the power MOSFET
source pin and the IC GND pin be
connected over as short a distance
as possible.
Notes on the detection level precision
protection function. Therefore, if this detection level varies with sample-to-sample variations or with tem-
perature, the operating current level of the overcurrent protection function of the power supply itself will vary.
Since variations in this level imply a need for increased ruggedness in parts used, or even the destruction of
circuit components, we have increased the precision of this IC as much as possible.
When the OVP circuit operates and the power supply current drops, this can induce a rise of the supply
Therefore, the circuit is provided with characteristics that cause the supply current to rise in constant
Due to these characteristics, if the
This circuit uses the fact that overcurrents in the power supply output are proportional to the current flowing
The current flowing in the main switch is detected by connecting a resistor between the power MOSFET
R6 and C6 in figure 12 form a
For the grounding point, we rec-
This overcurrent detection level is reflected on the operating current level of the power supply overcurrent
CC
. In the worst case, it may exceed the IC's guaranteed breakdown voltage (28 V).
CC
when the OVP circuit
To AC
CLM
GND
0.53 mA typ.
1.7 mA typ.
I
Figure 11. OVP operating circuit current
R6 R8 C6
CC
a
25 C. While this control operation is repeated
7.5 V 10 V
Figure 12
R7
AN8038, AN8038S
Use a capacitor
with excellent frequency
characteristics.
Use resistors with
no inductance.
18 V
V
CC
19