Application design solution based on AW329XX series OVP
In the consumer electronics and home appliance market, the power of electronic products in the past was relatively low, with common powers being 2.5W (5V/500mA) and 5W (5V/1A). As the charging power of electronic products has increased in recent years, 240W (20V/12A) charging power has been applied to mobile phones. The moment the charger is plugged into the terminal, a very high spike voltage is often generated. If this voltage exceeds the withstand voltage value of the chip on the charging path, it may directly cause damage to the chip. The function of the OVP chip is overvoltage protection. That is, after the input voltage exceeds a certain value, the output of the chip will be turned off to protect the subsequent circuit.
How to choose OVP chip?
The OVP chip has these key parameters: input voltage Vin, switch continuous current Isw, overvoltage protection voltage Vovlo, on-resistance Ron, and fast turn-off time toff. The above parameters require special attention when selecting.
Input voltage Vin The supply voltage cannot exceed the maximum input voltage of the OVP chip.
Switching continuous current Isw The supply current cannot exceed the maximum continuous output current of the OVP chip.
Overvoltage protection voltage Vovlo Vovlo needs to be greater than the operating voltage of the subsequent chip and retain a margin.
On-resistance Ron Due to the existence of on-resistance, a certain voltage drop (I*Ron) will occur through the OVP chip, and it will be accompanied by power loss, that is, heat generation.
Fast turn-off time toff When the OVP chip undergoes overvoltage protection and the output is completely shut down, it takes a certain time difference. This time is the OVP shutdown time. The shorter the toff, the better the OVP chip can protect the subsequent chip.
Working principle of OVP chip
AW32915AFCR belongs to Awinic OVP AW329XX series. It is an OVP chip with built-in 120V surge protection. It has functions such as wide input voltage, small on-resistance, and adjustable overvoltage protection voltage.
Input voltage range Vin: 3V-28V
Switching continuous current Isw: 5A
Overvoltage protection voltage Vovlo: default is 6.8V, adjustable range 4V-24V
On-resistance Ron: 27mΩ
Fast turn-off time: 50ns
The working principle of OVP is introduced in detail below. Figure 1 is the working timing diagram of AW32915AFCR.
figure 1 Stage 1
EN remains active low and the input voltage rises between UVLO (input undervoltage lockout, typical 2.9V) and the OVP trigger voltage Vovlo:
(1) After the debounce time tDEB + switching time tON, the internal MOS will be fully opened and the OUT terminal voltage will reach a stable value.
(2) When the input voltage exceeds UVLO and the duration reaches tSTART, the ACOK signal will be pulled low to notify the master that the input voltage is within the normal range.
EN remains in an active low state. When the input voltage exceeds the overvoltage protection voltage Vovlo, the OVP chip protection mechanism will be triggered:
(1) The internal mos tube will turn off the output after the tOFF time, and the voltage at the OUT terminal will gradually decrease to protect the subsequent circuit.
(2) At the same time, the ACOK voltage will be raised, notifying the main control OVP chip that overvoltage protection has occurred.
EN remains active low when the input voltage falls back below the overvoltage protection voltage Vovlo:
(1) After the debounce time tDEB + switching time tON, the internal MOS will be fully opened and the voltage at the OUT terminal will reach a stable value again.
(2) When the input voltage is less than the overvoltage protection voltage and continues for tSTART time, the ACOK signal will be pulled low to notify the main control that the input voltage returns to the normal range.
AW329XX is an OVP chip that is used to protect equipment from static electricity and surge damage. It is used in scenarios such as smartphones and tablets that require charging. The specific application location of the mobile phone is shown in Figure 3.
Figure 3 The application design of the AW329XX series OVP is shown in Figure 4. You need to pay attention to:
(1) If the design has surge requirements exceeding 120V, OVP needs to be used in conjunction with TVS
(2) When using the default threshold of OVP, R1 and R2 can be removed, and the OVLO pin of OVP can be directly connected to ground.
(3) If the default threshold of OVP is not used, R1 and R2 can be adjusted according to the design. The specific formula VIN_OVLO=((R1+R2)/R2)*1.2V
Awinic OVP chip
Currently, Awinic OVP's featured product AW32915A can meet conventional applications. If you need the OVP chip to have higher surge protection requirements, you can choose AW32605CSR. If you have low on-resistance requirements, you can choose AW32405CSR.
Review Editor: Huang Fei
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