FAQ - Track and Hold (T/H)

Q: Where is the "GND" pin on the RTH020?

A: The GND connection in the RTH020 is actually the package body itself. It is very important to connect the underside of the package to GND, not only for electrical purposes, but to dissipate heat as well. You can do this by exposing copper on the PCB where the chip will sit, and relieving that copper to GND with thermal vias. You can solder the chip body down to the exposed copper, or aid your connection with a thermally conductive epoxy.

Q: What is the PCB footprint for the RTH020?

A: The RTH020 leads were meant to lie flat on the board for optimal performance. The underside of the RTH020 package is the one and only ground contact for the package. With this in mind, you have two options for putting this part on a PCB.

Option 1: Cut-out and brass plate
In this option, you cut out completely the PCB where the body of the chip will sit; the hole is about 260 mils square. In this option, you need to attach a metal back plate to the board to serve as the ground contact and to dissipate heat. You can download the mechanical drawing of the back plate we use below. Keep in mind that the drawing in the file was designed for a .064" thick PCB. If your PCB is of different thickness, you will have to re-dimension the brass plate protrusion height. The back side of your board, where the metal plate will touch, needs to be all exposed metal and relieved to GND, since this plate will be connected to ground. This is very important, since this is the only ground connection for the chip, and we want to make it a good one.

• RTH020 Footprint (pdf) 
• EVRTH020 Socket Plate (pdf) 

  Option 2: Recessed ground plane
  Depending on your layer stack, this can be easy to do. From the top layer, make a recess 31 mils deep. The area of the recess should be around 260 mils square and must be all exposed metal and relieved to ground. You can liter the recess with thermal vias (relieved to GND) to aid your ground connection and to dissipate heat through the internal layers of the PCB. This method allows the chip to sit snuggly in the recess, with the pins laying flat on the top layer.

Q: Can the T/H stages in the device be clocked on irregularly spaced edges, assuming the relevant setup and hold time limits are not breached; or do the edges need to be regular, 50% duty, etc.?

A: Both T/H devices can be clocked on irregularly spaced edges (non-50% duty cycles). Just don't breach the relative setup and hold time limits.