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AP3105R Datasheet

High Voltage Green Mode PWM Controller

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Application Note 1062
High Voltage Green Mode PWM Controller AP3105
1. Introduction
The AP3105 is a low start-up current, current mode
PWM controller with green-mode power-saving
operation. Different from AP3103, AP3105 PWM
switching frequency at normal operation is fixed at
65kHz dithering with a narrow range. The difference
between AP3103/AP3105 is shown in Table 1. The
dithering of frequency will improve EMI feature.
When the load decreases, the frequency will reduce
and when at a very low load, the IC will enter the
“burst mode” to minimize switching loss. A
minimum 20kHz frequency switching is to avoid the
audible noise as well as reducing the standby loss. A
so-called VCC Maintain Mode is applied under light
load to realize a stable output and to reduce the loss
on the start-up resistor. The standby power of the
system using AP3105 can be reduced to 60mW at
230V input.
AP3103
AP3105
Frequency
Adjustable
Fixed at 65kHz
VFB Resistor
4.5k
10k
Standby
Performance
External Protection
VCC OVP
OLP & FOCP
Better
NA
Auto-recoverable
Auto-recoverable
Best
By “CTRL” pin
Latch
/Auto-recoverable
Latch
/Auto-recoverable
Table 1. The Difference between AP3103/AP3105
The AP3105 integrates a lot of functions such as the
Lead Edge Blanking (LEB) of the current sensing,
internal slope compensation and several protection
features which include cycle-by-cycle current limit
(OCP), fast OCP (FOCP), VCC over voltage
protection, OTP, OLP protection. The “CTRL” pin is
designed for customers to add external protection
functions such as OVP and OTP.
The AP3105 is specially designed for off-line
AC-DC power supply, such as LCD monitors,
notebook adapter and battery charger applications. It
can offer the designers a cost effective solution while
keeping versatile protection features. The IC uses
SOT-23-6 package type to realize its compact size.
This application note includes detailed explanation of
the IC’s major functions, some considerations about
Prepared by Wu Qikun
System Engineering Dept.
the PCB layout, and methods for reducing the
standby power loss, and finally presents a demo
design of a 12V 1A adaptor.
2. Function Description
2.1 CTRL Pin
For some applications, the system requires external
programmable protection function. The CTRL pin
has two kinds of modes to trigger the protection: high
level trigger and low level trigger. The low threshold
voltage is 0.5V and high threshold is 2.5V. When the
CTRL pin voltage is lower than 0.5V or higher than
2.5V, latch or auto-restart protection will be triggered
(different versions of 3105 offer different protection
combination, which is shown in Table 2).
Version VCC OVP
OLP&
FOCP
CTRL(low) CTRL(high)
AP3105
Auto-
recoverable
Auto-
recoverable
Latch
Auto-
recoverable
AP3105V
Latch
Auto-
recoverable
Latch
Latch
AP3105L
Latch
Latch
Latch
Latch
AP3105R
Auto-
recoverable
Auto-
recoverable
Auto-
recoverable
Latch
Table 2. Version Classification of AP3105
CTRL pin voltage maintains 1.6V if the pin is
floating, so leave CTRL pin open if the designer does
not need this function. Once the latch protection is
triggered, the bulk capacitor will provide the energy
to the IC through start-up resistor to ensure the IC
disable the output signal (latch mode). This mode
will not be released until the AC input is shut off.
Therefore, the de-latch time is mainly depending on
the value of HV startup bulk capacitor. If the system
needs a short de-latch time, it is better for the startup
resistor to take power from the point before the
rectifier bridge. Typical application of CTRL pin is
shown in Figure 1.
Note:
1. The sink current to the CTRL pin should be lower
than 5mA by selecting a proper pull up resistor.
2. If the designer needs to apply a bypass capacitor
on CTRL pin, the capacitor should not be more than
1nF.
Apr. 2011 Rev. 1. 0
BCD Semiconductor Manufacturing Limited
1


Diodes Semiconductor Electronic Components Datasheet

AP3105R Datasheet

High Voltage Green Mode PWM Controller

No Preview Available !

OVP and OTP
OVP
OTP
Figure 1. CTRL Pin Application
2.2 Fast OCP Function
When the load is short-circuited, the power converter
can be protected by OLP protection. But if the output
filter inductor and the secondary Schottky is
short-circuited, the transformer will be immediately
saturated resulting in the breakdown of the MOSFET
due to high voltage stress. The AP3105 bears built-in
fast OCP function to alleviate the saturation of the
transformer and reduce the voltage stress of
MOSFET. The FOCP position and FOCP waveform
are shown in Figure 2 and Figure 3. When the
secondary Schottky and the output filter inductor is
short-circuited, the power converter can trigger latch
or auto-restart immediately within several switching
cycles with fast OCP. The FOCP threshold on FB pin
is 1.8V.
Fast OCP
Application Note 1062
2.3 VCC Maintain Mode
Under ultra light load or load transient condition, VFB
will drop to lower than 1.4V, thus the PWM drive
signal will be stopped, and there is no more new
energy transferred due to no switching. Therefore, the
IC supply voltage may drop to the UVLO (off)
threshold and the system may enter the unexpected
restart mode. To avoid this situation, the AP3105
holds a so-called VCC maintain mode which can
supply energy to VCC. When VCC decreases to a
setting threshold (10.1V), the VCC maintain
comparator will output a drive signal to make the
system switch and provide a proper energy to VCC
pin. When VCC increases to 10.6V, the gate signal
will be stopped. The VCC maintain function will
cooperate with the PWM and the burst mode loop to
make the output voltage variation be within the
regulation. This mode is designed for reducing
startup resistor loss and it will achieve a better
standby performance with low value VCC capacitor
and larger startup resistor. The VCC will not reduce
to the UVLO (off) threshold during the startup
process and under ultra light load or load transient
condition. To avoid the “VCC maintain mode”
triggering in normal operating condition, it is
suggested to design the VCC value higher than VCC
maintain threshold under minimum load condition.
The processing of VCC maintain mode is shown in
Figure 4.
Burst mode
VCC maintain mode
FB
1.4v
Figure 2. FOCP Position
Diode shorten
VCC
FB
SENSE
Figure 3. FOCP Waveform
Apr. 2011 Rev. 1. 0
vcc
10.6v
10.1v
Gate
Load decreasing
Figure 4. The Process of VCC Maintain Mode
3. PCB Layout Consideration
3.1 High Frequency Loop Consideration
As shown in Figure 5, there are four major high
frequency current loops:
1. The current path from bulk capacitor, transformer,
MOSFET, RCS returning to bulk capacitor
2. The path from GATE pin, MOSFET, RCS returning
to the ground of IC
BCD Semiconductor Manufacturing Limited
2


Part Number AP3105R
Description High Voltage Green Mode PWM Controller
Maker BCD
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AP3105R Datasheet PDF






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