Table of contents
Explanation of technical terms
overview
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How to use a switching regulator with analog ground plane (AGND) and power ground plane (PGND)?
This is a question many developers ask when designing a switching power supply. Some developers are used to dealing with digital and analog ground planes; however, their experience often fails when it comes to power GND. Designers often simply copy the board layout of the chosen switching regulator. Stop thinking about it.
overall architecture process
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Solder contacts to PGND and AGND connections.
Explanation of technical terms
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1.DCDC：
DC/DC means a device that transforms a DC power supply of a certain voltage level into a DC power supply of another voltage level . DC/DC is divided into two types: step-up power supply and step-down power supply according to the voltage level transformation relationship , and is divided into two types: isolated power supply and non-isolated power supply according to the input-output relationship. For example, the DC/DC converter connected to the vehicle-mounted DC power supply converts high-voltage direct current into low-voltage direct current.
2.PGND:
is the ground connection through which higher pulse currents flow. According to the switching regulator topology. This represents the current through a power transistor or the pulsed current of a power driver stage. This ground plane is especially important for switching controllers with external switching transistors.
3.AGND:
Sometimes called SGND (signal ground plane). This is the ground connection that other signals use as a reference. Usually very calm. This ground plane includes the internal reference voltage needed to regulate the output voltage. The soft-start and enable voltages are also referenced to the AGND connection.
4. Switching Slew Rate
The switch switching speed formula is: According to tTRANSITION=200ns(typ.), a maximum switching frequency can be calculated, that is, 1/(200ns)=5MHz, but at this time the output waveform becomes a triangle wave. Usually, tTRANSITION is required to account for 10% of the switch state, and it can be calculated that the operating frequency of the analog switch is 1/(10*200ns)=500KHz.
5.IC
An integrated circuit (integrated circuit) is a tiny electronic device or component. Using a certain process, the transistors , resistors , capacitors , inductors and other components required in a circuit are interconnected, and they are fabricated on a small or several small semiconductor wafers or dielectric substrates, and then packaged in a tube . , and become a microstructure with required circuit functions; all the components in it have been structurally integrated, making electronic components a big step towards miniaturization, low power consumption, intelligence and high reliability. It is represented by the letters " IC " in the circuit . The inventors of the integrated circuit are Jack Kilby (germanium (Ge)-based integrated circuits) and Robert Noyce (silicon (Si)-based integrated circuits). Most of today's semiconductor industry uses silicon-based integrated circuits.
technical details
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1. Know 1
According to one view, the AGND and PGND connections on a switching regulator IC should be connected to each other next to their respective pins. This way, the voltage offset between the two pins is kept relatively low. Therefore, the switching regulator IC can be protected from interference. thereby avoiding damage. All ground connections and possible ground planes of the circuit will be connected to this common point in a star topology.
2. Know 2
Another view is to separate AGND from PGND on the board to form two separate ground planes that are connected to each other at one point. through this connection. The interference signal (voltage offset) mainly appears in the PGND area. The voltage in the AGND area is still very quiet. and well decoupled from PGND. However. According to the pulse current transient and current intensity. There may be a significant voltage offset between PGND and AGND on the respective pins. This may cause the switching regulator IC not to work properly, or even be damaged.
3. Comprehensive
After all. The grounding problem is actually a trade-off: separating the two ground planes has the advantage of isolating noise and interference;
But there may be a voltage offset between the two ground planes. There is a risk of damaging the chip and affecting functionality. After weighing the pros and cons. Whether the final decision is correct or not mainly depends on the IC design, including the switching speed. Power level. Parasitic inductance on bonding wire and IC package. Door-to-door risk per IC design (involving different semiconductor processes).
summary
On how to deal with the issue of AGND and PGND grounding. There are no easy answers. So the discussion is still going on. We mentioned earlier that many switching regulator users follow the board layout and ground connection types in the example circuits provided by the IC manufacturer. This is very useful. Because you can usually assume that the manufacturer also tested each IC with this configuration. And, in Figure 1 and Figure ? As can be seen in the examples provided, the respective IC pinouts are suitable for local ground connections next to PGND and AGND. Or suitable for separate grounding.