SSRP LTC1746 Assembly Manual V0.1 Check the most recent version http://oscar.dcarr.org/ssrp/hardware/ltc1746/ltc1746.php Introduction This manual details the general assembly process for the SSRP LTC1746 ADC board. For information concerning setup and operation of the SSRP and LTC1746 board please see the SRRP LTC1746 Manual available at the above website. Tools/Materials Required Soldering iron SMT tweezers Fine gauge solder Paste or liquid flux Solder wick Dikes or wire clippers Getting Started Before starting assembly, inspect the supplied parts to ensure that all are in good condition and that none are missing. Additionally, use a soft cloth to wipe down the PCB board to remove any residue that may prevent a solid solder bond. After the board is clean, inspect the traces and pads closely. Look for signs of damage such a broken traces or missing pads. A quick note about electrostatic discharge (ESD): Some of the parts on the LTC1746 board are sensitive to damage from ESD. Ideally, the board would be assembled on a static dissipative mat while wearing a grounded wrist strap. However I realize that many individuals do not have access to such tools. If a few precautions are taken much of the potential for damage can be eliminated. Touching a grounded object such as a faucet before working and avoiding handling parts more than necessary will go a long way. Installing the ICs Before any other components are installed, its best to place and solder the
LTC1746. Remove the LTC1746 from its tube using tweezers or a vacuum pickup tool. Be very careful not to bend any of the pins on the device, otherwise the pins will not correctly contact the pads, making soldering very difficult. Place the LTC1746 on the PCB, noting the orientation of pin 1. Gently align the device with its pads and then tack the opposite corners of the chip using a fine tipped iron. Before soldering the remainder of the pins, double check the alignment of the device. If everything looks okay, apply a liberal amount of flux and solder the remainder of the pins using your preferred technique. Use solder wick to remove any shorts between pins. Install the LP2989 and THS4501 in the same manner (pay careful attention to orientation). Installing the Passive Components The next step is to place and solder the passive components on the board. Let's start with C12, a 10uF 1210 capacitor. First locate the C12 pads using the component placement guide and the PCB silkscreen. Apply a small amount of solder to one of the pads. Place a small amount of flux on the solder. Locate the part and pick it up using the tweezers. Heat the small amount of solder on the pad and slide the component into place while the solder is molten. Remove the iron and wait until the solder has hardened before releasing the component. Now that the component is held in place, you may solder the other side using a conventional technique. After the second side has been soldered, its a good idea to reflow the first joint to avoid cold joints. Using this technique, install the remainder of the capacitors, resistors and LEDs. Zero ohm resistors, R13, R14 and R15 are used to select either high or low speed mode. The LTC1746 Manual has information on which mode to select and which resistors to install. Note the polarity of the two tantalum capacitors and the LEDs. On the tantalum capacitors, the bar indiates the positive side of the capacitor. This is an arrow on the bottom of the LEDs that indicates the anode and cathode. If the board is oriented component side up with the multi-pin connector on the left then LED1's arrow should point to the left and LED2's arrow should point up. Installing the Through-hole Components The through hole components on the board are the power jumper, the crystal oscillator socket, the SMA connector and the multi-pin connector. The power jumper connects the two large vias as shown below. Cut a piece of the include wire and insert one end into each via. Route the jumper on the component and solder on the bottom.
Jumper Location (highlighted) Before the crystal oscillator socket is installed, clip the middle four pins off so that only the pins at the corners remain. Then solder it in place. Following the crystal oscillator, install the SMA connector. I recommend soldering the center pin first and then the four ground lugs. Lastly install the multi-pin header so that the pins point downwards and the solder joints are on the top side of the board. Finishing Touches At this point the board is almost complete. The steps that remain are to connect the analog and digital ground planes and to attach the power leads. To connect to the ground planes, turn the board over and solder a small piece of wire (resistor lead or similar) between the two large SMT resistor pads on the bottom of the board. The pads are located directly underneath the LTC1746. Lastly, install some sort of power leads or connector on the power lead pads located on the edge of the board near the LP2989 chip. Bring Up Before bring-up the crystal oscillator should be installed. Most oscillators will have one corner that is more pointed than the others or will have a dot or other marking
in one corner. You will notice that the silkscreen around the oscillator socket also has one corner that is more pointed than the others. Insert the oscillator into its socket so that the markings on the board and oscillator are aligned. After the oscillator is installed the board can be powered. Ideally, power should initially be applied using a 0-5V variable supply and a series ammeter. If a variable supply is not available the ammeter should still be used. When 5-8VDC is applied, the board should consume approximately 100-120ma. Do not exceed 8V as the LP2989 will overheat.
Component List Board Reference Part Description C1 0603 12pF ceramic capacitor C2 0603 12pF ceramic capacitor C3 0603 12pF ceramic capacitor C4 C5 0805 4.7uF ceramic capacitor C6 C7 C8 C9 1206 4.7uF ceramic capacitor C10 C11 C12 1210 10uF ceramic capacitor C13 1210 10uF tantalum capacitor C14 1210 10uF ceramic capacitor C16 C17 C18 C19 0603.01uF ceramic capacitor C20 C21 C24 1206 2.2uF tantalum capacitor C25 0603.01uF ceramic capacitor LED1 0603 LED green LED2 0603 LED green QG1 DIP-8 machined socket R1 R2 R3
Board Reference Part Description R4 R5 0603 392 Ohm resistor R6 0603 392 Ohm resistor R7 0603 412 Ohm resistor R8 0603 383 Ohm resistor R9 0603 54.9 Ohm resistor R10 0603 280 Ohm resistor R11 0603 340 Ohm resistor R13 0603 0 Ohm resistor R14 0603 0 Ohm resistor R15 U1 Linear Technology LTC1746 ADC U2 TI THS4501 differential ppamp U3 2x20.1 male pin header U23 National Semi. LP2989 linear regulator X1 R/A male SMA pcb jack
Component Locations
Assembled Board