Hi everyone,
I'm currently designing a small PCB to measure the pressure out of a wheatstone bridge. I use a conditioner from Texas Instruments (PGA309) and the ADS1251 (24bits) to convert in digital format.
I decided to separate the ground and power planes between digital and analog parts, to increase the quality of the results. I read many things about this, but I'll be pleased to have an external point of view of my design. It use 4 layers (signal-gnd-power-signal), and a picture is attached to this post
Right after the power input, there is a power-on switch and a 5V regulator (low noise). Then the 5V output goes to the power plane with three vias and a decoupling capacitor. The ground "star" point is placed just above the regulator output, with a "analog return path" for the analog current. The noise from the digital part (MSP430) should not go this way (almost not) ?
On the left there is the analog part, with a voltage reference (followed by a OPA) and the the ADS1251 just under the PGA309. SPI lines and CLK lines have a 50 ohm resistor in serie and a TVS diode.
Two schottky diodes are mounted back-to-back with a resistor (1ohm) to reduce the ground potential difference (read in this article, fig2 : http://www.ti.com/lit/an/slyt499/slyt499.pdf)
I'd like to have an expert view to tell me if something look wrong or if I can improve this design in any way. I read that separating the planes could create a dipole antenna (or tripole in this case?). So maybe it is better to make only one power-plane and one ground plane for all...
Thanks in advance,
I'm currently designing a small PCB to measure the pressure out of a wheatstone bridge. I use a conditioner from Texas Instruments (PGA309) and the ADS1251 (24bits) to convert in digital format.
I decided to separate the ground and power planes between digital and analog parts, to increase the quality of the results. I read many things about this, but I'll be pleased to have an external point of view of my design. It use 4 layers (signal-gnd-power-signal), and a picture is attached to this post
Right after the power input, there is a power-on switch and a 5V regulator (low noise). Then the 5V output goes to the power plane with three vias and a decoupling capacitor. The ground "star" point is placed just above the regulator output, with a "analog return path" for the analog current. The noise from the digital part (MSP430) should not go this way (almost not) ?
On the left there is the analog part, with a voltage reference (followed by a OPA) and the the ADS1251 just under the PGA309. SPI lines and CLK lines have a 50 ohm resistor in serie and a TVS diode.
Two schottky diodes are mounted back-to-back with a resistor (1ohm) to reduce the ground potential difference (read in this article, fig2 : http://www.ti.com/lit/an/slyt499/slyt499.pdf)
I'd like to have an expert view to tell me if something look wrong or if I can improve this design in any way. I read that separating the planes could create a dipole antenna (or tripole in this case?). So maybe it is better to make only one power-plane and one ground plane for all...
Thanks in advance,