LCD Display Inverter

Display Inverter / VGA Board / LCD Controller

How to stabilize the voltage? You need a correct “posture”

Bypass capacitors are often required during Electronic product development. Figure 1 shows a switching regulator that can generate a low voltage from a high voltage. In this type of circuit, the bypass capacitor (CBYP) is especially important. It must support switching currents on the input path so that the supply voltage is stable enough to support device operation.

Bypass capacitors are often required during electronic product development. Figure 1 shows a switching regulator that can generate a low voltage from a high voltage. In this type of circuit, the bypass capacitor (CBYP) is especially important. It must support switching currents on the input path so that the supply voltage is stable enough to support device operation.

How to stabilize the voltage? You need a correct “posture”
Figure 1. ADP2441 switching regulator with bypass capacitor C at the inputBYP.

Because the input capacitance in a buck converter is part of the critical path (hot loop) for this topology, CBYP The connections must ensure as little parasitic inductance as possible. Therefore, the mounting position of this component is critical. The left side of Figure 2 shows a not so good layout. Thin traces to bypass capacitors. The current flowing into the voltage converter also does not flow directly from the bypass capacitor. The bypass capacitor only touches the main circuit slightly. This increases the parasitic inductance created by the capacitor and reduces the effect of this component. The layout shown on the right side of Figure 2 is recommended, as bypass capacitors are very efficient. The connection itself produces only a very small amount of parasitic inductance. It can also be seen from the figure that the pinout of the converter (eg switching regulator) can have an impact on the layout of the board. As can be seen from the right side of Figure 2, VINAnd the GND pins are close together, even closer than the less well-placed left. In this way, the loop area between the bypass capacitor and the IC will be smaller.

How to stabilize the voltage? You need a correct “posture”
Figure 2. Unfavorably connected bypass capacitors (left) and favorably connected bypass capacitors (right).

Because the connection of the bypass capacitor should ensure as little parasitic inductance as possible, it is recommended to place the bypass capacitor and the switching regulator on the same side of the board. However, in some applications, the front-side switching regulator can only be decoupled from the bypass capacitor at the bottom of the board. This is the case when there is not enough room for larger decoupling capacitors. In this case, vias are used to connect the capacitors. Unfortunately, vias create a parasitic inductance of several nanohenries. To minimize the impedance of this connection, various connection suggestions have been made, as shown in Figure 3.

How to stabilize the voltage? You need a correct “posture”
Figure 3. There are various connection options when bypass capacitors are connected to through holes.

Version A is not very favorable. In this option, a thin wire connection is used between the via and the bypass capacitor. Depending on where the support path runs on the other side of the board, this layout arrangement can also lead to increased parasitic inductance.

In version B, the vias are located closer to the bypass capacitors, so this connection is advantageous. Also, two vias are used in parallel. This reduces the overall inductance of the entire connection.

Version C is more advantageous, where the loop area of ​​the connection is very small, so only a very small amount of parasitic inductance is generated. However, because the bypass capacitors are very small and the cost of the manufacturing process is low, it is not possible or possible to make vias under the components.
Version D provides a very interesting connection. Depending on how a particular ceramic bypass capacitor is designed, the lateral connection to the board may create the least amount of parasitic inductance.

The placement of the bypass capacitors on the board is critical for these components to be efficient. That is, it is important to use the connection with the lowest possible parasitic inductance. Proper connections should use the same side of the board as the circuit, as shown in Figure 2. In some special cases, it may be necessary to connect bypass capacitors on the back of the board, in which case the connection should be chosen with the lowest possible parasitic inductance as shown in versions B, C, and D of Figure 3.

The Links:   G084SN05 V9 LQ104S1LG33