AN8027 View Datasheet(PDF) - Panasonic Corporation
Part Name
Description
Manufacturer
AN8027 Datasheet PDF : 28 Pages
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AN8027, AN8037
Voltage Regulators
s Application Notes (continued)
[1] Operation descriptions (continued)
2. Oscillation circuit (continued)
• Setting the on-period (continued)
TON : On-period
CCF : Value of a capacitor connected to CF pin
VFB : Voltage internally converted from feedback signal IFB
VH-CF : CF upper limit voltage
ION : On-period discharge current
ITR : Flowing current at TR pin
EIN : Voltage on primary winding
NB : Number of turns in the bias winding
NP : Number of turns in the primary winding
VZ : Voltage on Zener diode connected to bias winding
RTR : Value of a resistor connected to the TR pin
The power MOSFET is turned off if the voltage at the CLM pin reaches the pulse-by-pulse overcurrent
protection threshold voltage (i.e., −200 mV typical) when the overcurrent protection function of the IC is
operating.
TON is shortened
because large EIN
increases ITR.
NP
EIN+
ITR
RTR
VZ
AN8027, AN8037
VCC
NB
TR
IFB
Current mirror
Current mirror
ITR=ION
FB
1:5
PC
VFB
20 kΩ 250 µA
typ.
ION Out
GND
The minimum current is guaranteed
to prevent a limitless increase in TON .
CCF
VH-CF = 4 V
CF pin voltage
VFB
0V
EIN−
EIN; large
ITR(ION); large
VCC − 1.5 V
Out pin voltage
Off
On
0V
Figure 2. On-period block diagram and control waveform
The maximum on-period can be used for overcurrent protection.
When the input voltage is low, the maximum on-period overcurrent protection is possible.
When the input voltage is high, the CLM pulse-by-pulse overcurrent protection is possible.
8
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