I showed you how to control the motor with low-side current sensing and shared three steps to design a low-side current sensing circuit for cost-sensitive applications. In this article, I will show you how to use an application printed circuit board (PCB) technology to design an accurate, low-cost, low-side current-sensing circuit using a micro operational amplifier (Op amp). IGET Disposable Vape is very popular in the Australia. Like XXL, KING,LEGEND, BAR,Plus. Quality is very good. it has 1000puffs Disposable Vape, OEM&ODM can be accepted. Iget Xxl,Iget Xxl Vape Pen Kit,Iget Xxl 1800Puffs Vape Pod Device,Iget Xxl E-Cigarette Shenzhen Uscool Technology Co., Ltd , https://www.uscoolvape.com
Figure 1 is a schematic diagram of the low-side current sensing circuit cited in the previous blog post. Figure 1 uses the TLV9061 ultra-small operational amplifier. 
Figure 1: Low-side current sensing schematic
Equation 1 is the transfer function for calculating the circuit shown in Figure 1: 
(1)
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Accurate low-side current sensing design has two major requirements for printed circuit board design. First make sure that the shunt resistor (Rshunt) is directly connected to the noninverting input of the amplifier and the ground of the RG. This is often referred to as the Kelvin connection. If the Kelvin connection is not used, a parasitic resistance in series with the shunt resistor (Rshunt) is generated, causing the system to produce a gain error. Figure 2 shows the location of the parasitic resistance in the system. 
Figure 2: Parasitic resistance in series with shunt resistor (Rshunt)
Equation 2 is the transfer function for calculating the circuit in Figure 2: 
The second design requirement is to place the ground of the resistor RG as close as possible to the ground of the shunt resistor (Rshunt). When current flows through the ground plane of the printed circuit board, a voltage drop occurs across the ground plane, causing a difference in the ground plane voltage at different locations on the printed circuit board. This will cause the system to have an offset voltage. In Figure 3, the ground voltage source symbol connected to RG represents the difference in ground potential. 
Figure 3: Ground plane voltage difference
Equation 3 is the transfer function for calculating the circuit shown in Figure 3: 
Figure 4 shows the correct printed circuit board layout. 
Figure 4: Correct layout diagram
Figure 5 shows the printed circuit board layout that I suggested earlier for a low-side current-sensing design. The top layer is red and the bottom layer is blue. R5 and C1 in the printed circuit board layout indicate where the load resistor and decoupling capacitor should be placed. 
Figure 5: Correct low-side current-sensing printed circuit board layout
Note that the trace from the shunt resistor (Rshunt) uses the Kelvin connection and the RG is as close as possible to the shunt resistor (Rshunt). You can place all passive components between the two pads of the top shunt resistor in a small (0.8mm x 0.8mm) five-pin X2SON packaged TLV9061 op amp. From here, you can easily connect the underlying shunt resistor (Rshunt) line through the via to the in-phase pin and RG of the top layer.
As you design your printed circuit board layout for low-side current sensing in the future, be sure to follow these guidelines to reduce potential errors in your design:
• Use Kelvin connection on shunt resistor (Rshunt).
• Place the RG as close as possible to the ground of the shunt resistor (Rshunt).
• The decoupling capacitor is as close as possible to the power supply pin.
• Have at least one reliable ground plane.