Document
Application Note 1096
High Voltage Green Mode PWM Controller AP3105NA/NV/NL/NR
Prepared by Wu Qikun System Engineering Dept.
1. Introduction
The AP3105NX is a low start-up current, current mode PWM controller with green-mode power-saving operation. Different from AP3103, AP3105NX’s PWM switching frequency at normal operation is fixed at 65kHz dithering with a narrow range. The difference between AP3103 and AP3105NX 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 to reduce 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 AP3105NX can be reduced to 60mW at 230V input.
AP3103 Frequency VFB Resistor Standby Performance External Protection VCC OVP Adjustable 4.5kΩ Better NA Auto-recoverable Auto-recoverable AP3105NX Fixed at 65kHz 10kΩ Best By “CTRL” pin Latch /Auto-recoverable Latch /Auto-recoverable
This application note includes detailed explanation of the IC’s major functions, some considerations about the PCB layout, and methods for reducing the standby power loss, and finally presents a demo design of a 12V 2A 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 voltage 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 AP3105NX offer different protection combinations, which are shown in Table 2).
Version
AP3105NA
VCC OVP
Autorecoverable Latch Latch Autorecoverable
OLP& FOCP
Autorecoverable Autorecoverable Latch Autorecoverable
CTRL (Low)
Latch Latch Latch Autorecoverable
CTRL (High)
Autorecoverable Latch Latch Latch
AP3105NV AP3105NL AP3105NR
OLP & FOCP
Table 2. Version Classification of AP3105NX Table 1. The Difference between AP3103/AP3105NX
The AP3105NX 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 AP3105NX is specially designed for off-line AC-DC power supply, such as LCD monitors, notebook adapters and battery charger applications. It can offer the designers a cost-effective solution while keeping versatile protection features. The IC uses the SOT-23-6 package type to realize its compact size.
Dec. 2012 Rev. 1. 0 1
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
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Application Note 1096
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.
Figure 2. Shorter OLP Delay Time
OVP and OTP
OVP
OTP
Figure 1. CTRL Pin Application
2.2 Difference of AP3105&AP3105NX Table 3 shows the difference AP3105&AP3105NX.
AP3105
OLP Delay Time VCS Adjustable @ start-up
between
AP3105NX 100ms@start-up 64ms@normal operating Adjustable
48ms@start-up 32ms@normal operating NA
Figure 3. Longer OLP Delay Time
Table 3. AP3105 vs. AP3105NX
2.3 Longer OLP Delay Time for Capacitive Load A capacitive load needs more power to be charged at start-up time. One solution is to enlarge the OCP point and keep the same start-up time, otherwise it will trigger OLP protection mode. Another solution is to extend the OCP delay time, which can simplify the transformer design since it is no need to rise the OCP point. Thus AP3105NX makes the OLP delay time longer to 100ms at start-up state and 64ms at operating mode. If FB pin’s value is over 4V for 64ms at operating state or for 100ms at start-up, IC will enter OLP mode to limit the input power. Figure 2 and Figure 3 show the startup state with different OLP de.