Application of VMA series digital audio power amplifier module

Audio power amplifiers can be said to be a long-standing field in the electronics industry. In terms of device types, it has gone through the development process of electron tubes, transistors, integrated circuits, and hybrid circuits; in terms of circuit form, there are Class A , Class B , Class AB , etc. These devices and circuits have their own characteristics, and each can produce superior products.

With the advancement of electronic technology in recent years, a new type of audio power amplifier circuit - Class D audio power amplifier is being used more and more widely. Class D power amplifier is different from traditional analog power amplifier. It does not directly drive the speaker through voltage, but adjusts the audio signal to a PWM signal with a much higher frequency (several hundred KHz ) , and then uses this signal to drive the inductive speaker coil to restore the sound. Compared with traditional power amplifiers, the biggest feature of Class D power amplifiers is high efficiency. A large part of the power of traditional Class A power amplifiers is dissipated in the driving circuit, so the efficiency is very low, usually only 20%-30% . This is obviously not in line with the trend of contemporary green energy saving. Class D power amplifiers are very efficient (up to 90% ) because they use PWM mode . Therefore, for the same output power, traditional Class A power amplifiers require a much larger power supply and a large area of ​​​​heat sink. The power demand of Class D power amplifiers is only about 1/4 of that of Class A power amplifiers with the same power , and because of the low heat generation, usually only a small heat sink is required or even no heat sink is required. In addition, the circuit of Class D amplifier is usually simpler, so it can save a lot of space, so the failure rate is much lower than that of traditional analog amplifiers.

Although Class D amplifiers, as a relatively new amplifier circuit, are often criticized by many audiophiles for problems such as "digital sound", both instrument tests and actual listening tests show that the sound quality of Class D audio amplifiers is no less than that of traditional analog amplifiers. In the foreseeable future, energy-saving and environmentally friendly Class D amplifiers will become the mainstream of audio power amplifiers and be widely used.

VMA Series Digital Audio Amplifier Module Introduction

The VMA series digital audio amplifier module is a high-quality miniature Class D audio amplifier module launched by Beijing Ruiyufei Technology Co., Ltd. There are currently 5 models. The VMA series amplifier module has the following features:

All the devices required for power amplifier are integrated inside . Usually, the signal path does not need any external components to form a high-quality power amplifier circuit.

lThe module adopts a highly efficient design without output inductor, so the size of the module is very small, only similar to the size of a stamp. And because of the edge half-hole design, this module is also vividly called "stamp amplifier" by many users.

l High power density. Take VMA2016 as an example, it can output 10Wx2 power at 8Ω load with a size of only 15mmx25mmx3.8mm .

l Low heat generation, high efficiency, energy saving and environmental protection. Taking VMA2015 as an example, even under the full load of 15W , the module does not need a heat sink, and the shell only feels warm.

l The peripheral circuit is very simple, no heat sink and high-power power supply are required, which greatly reduces the system cost.

The current 5 models and parameters of the VMA series amplifier modules are shown in the following table

Among them, VMA2013 and VMA2015 are pin-pin compatible, and VMA2014 and VMA2016 are pin-pin compatible. They only differ in power and can be directly interchanged.

The picture below is a physical photo of the VMA2016 power amplifier module.

Figure 1: VMA2016 stereo power amplifier module

It can be seen that even the module with the highest output power in this series is only about the size of a coin. The advantage of small size makes VMA series chips very useful in some space-limited applications such as car audio, battery-powered audio, handheld devices, etc. The following introduces the members of this series one by one:

VMA2012

VMA2012 is the first model in this series, but it can only be regarded as a little brother in terms of output power. However, the power of 2.5wx 2 should not be underestimated, and it can make your small desktop speaker sing clearly in the whole room. The biggest feature of this model is the low power supply voltage, which only needs 2.7V to work normally, and the maximum cannot exceed 5.5V . In other words, only 2-3 dry batteries are needed to power the VMA2012 , which can drive a small 8- ohm speaker to fill a room of more than ten square meters with wonderful music. This is incredible for traditional analog amplifiers.

Below is the pinout of VMA2012 and the Altium Designer device library provided by Ruiyufei Technology Co., Ltd.:

Figure 2 VMA2012 pin diagram and component symbols

The VMA2012 module still uses the PQN-12 package common to the VM series modules , with a size of 15x18x 3.8mm , very small. The pinout of VMA2012 is as follows:

It is very simple to design a stereo amplifier using VMA2012 . Usually only two resistors are needed to set the gain. If the voltage gain of 20 times is just right, even these two resistors can be omitted. The small size, low cost and low voltage characteristics make VMA2012 very suitable for high-end radios, portable small stereos, desktop stereos and other occasions.

The figure below is the reference design circuit of VMA2012 :

Figure 3 VMA2012 reference design

The reference design in the figure above adopts a single-ended input design, which is suitable for directly connecting to MP3 and other audio sources. Of course, it can also be designed as a differential input mode for interfacing with codec and other devices.

The voltage gain is set by two resistors Rg1 and Rg2 . The gain is calculated as: (V/V)

From the gain formula, we can infer that if Rg is omitted and the input signal is directly connected to the module, the maximum gain of VMA2012 is 20 times. Such gain is just suitable for MP3 and other audio sources to drive small desktop speakers. If there is a special need for higher gain, we can manufacture it according to customer requirements.

The following figure shows an amplifier board made by a user using the VMA2012 module. Its size is only the size of a CF card, and it can be installed in a very small space to make an ultra- mini amplifier. One user commented that its sound quality "exceeded expectations and can fully meet general music appreciation requirements."

Figure 4 Amplifier board designed with VMA2012 [page]

VMA2013/VMA2015

VMA2013/2015 is a single channel high power audio amplifier module. When the load is 8 Ω , the output power of VMA2013 is 6W , and that of VMA2015 is 15W . When the output is half power, the THD+N of the module is only 0.07% . The appearance and pins of the two chips are exactly the same, so they can be used interchangeably. The module package pins and device diagram are shown below:

Figure 5 VMA2013/2015 pin diagram and component symbols

The VMA2012 module uses the PQN-12 package common in the VM series modules , with a size of 15x18x 3.8mm The pin description of VMA2012 is as follows:

It is also very simple to design the power amplifier circuit using VMA2013/2015 . In the most simplified case, no external components are needed. Of course, in order to improve the sound quality, especially in the case of high power output, we still recommend adding a power filter capacitor of 1000uF or more. The larger the capacitor, the more beneficial it is to improve the large dynamic response. In addition, in the specific design, G0 and G1 can be designed in the form of jumpers to set different gain values. The following figure is the reference circuit diagram of VMA2013/2015 :

Figure 6 VMA2013/2015 reference design circuit diagram

The reference design in the figure above is a single-ended design, in which case IN- is directly grounded. G0 , G1 , and VR can be set using jumpers on the PCB .

The picture below is a 15Wx2 stereo power amplifier board designed with VMA2015 . By comparison, we can see that the size is only slightly larger than a CF card, but the output power can reach 15Wx2 , which fully demonstrates the advantage of high power density of VMA series modules.

Figure 7 15Wx2 stereo amplifier board designed in 2015

VMA2014/VMA2016

VMA2014/VMA2016 is a medium / high power stereo audio amplifier module. The output power of VMA2014 is 5Wx2 at 8 Ω load , and the power of VMA2016 is 10Wx2 . At half power output, THD+N is only 0.07% , and SNR is as high as 97dB . The appearance size and pins of the two chips are exactly the same, so they can be used interchangeably. The module package pins and device diagram are shown below:

Figure 8 VMA2014/2016 pin diagram and component symbols

The VMA2012 module uses the PQN-18 package common to the VM series modules , with dimensions of 15x25.4x 3.8mm The pin description of VMA2012 is as follows:

Figure 9 VMA2014/VMA2016 reference circuit

The reference design in the figure above is a single-ended input, in which case IN- is directly grounded. G0 , G1 , and VR can be set using jumpers on the PCB .

The picture below shows a 10Wx2 stereo amplifier board designed with VMA2016 . Its size is similar to that of a CF card and can be easily placed in many small speakers and other audio entertainment devices.

Figure 10 10Wx2 stereo amplifier board designed with VMA2016

At present, VMA2016 has been widely used in car audio and desktop audio. Its excellent sound quality, small size, simple circuit and high cost performance have won unanimous praise from users. Some users commented: " Good quality, very balanced high and low frequencies, delicate and pleasant sound quality, delicate high frequencies, and good low frequency volume"; "Very power-saving, turned on to normal volume, just right for listening to string music 2 meters away from the speaker, current consumption is about 100mA "; "The heat generation is very small, at normal volume, the circuit is only slightly warm."

Welding of VMA series modules

The VMA series modules are packaged with high temperature resistant materials, so they can be soldered using reflow soldering. It is also very convenient to solder with an electric soldering iron in amateur conditions. Prepare a pointed soldering iron and some thin solder wire ( 1mm The following is the best). First, apply some flux on the pad, then put the module in the correct position so that the pins on the module correspond to the pads one by one. Put the solder wire into the half-hole gap, and gently touch the solder wire with the soldering iron. Soon the solder will melt and firmly solder the module's half-hole pad to the pad on the bottom plate. The soldering operation is shown in the figure below:

Figure 11 Manual soldering of VMA series modules