Rev G


The EVAL137 evaluation kit provides a convenient method to become familiar with the operation of amplifier model PAD137 before your application circuit is committed to production. Some assembly is required since user selections are needed depending on the application. For example, a current limit resistor value needs to be selected by the user. Also, there are several PCB mounting options available.

Critical connections for power supply bypassing and compensation are pre-wired. Connections are also provided for implementing fold-over current limit as well as standard current limit with the optional PAD125 Current Limit Accessory Module. Fold-over current limit components are not provided since each application will have different
requirements. Connections are provided for the optional PAD130 or PAD132 Power Supply Accessory Modules and also the PAD131 Fan Controller Accessory Module. Diode clamps on each power supply and the output connections are
provided for those applications in which significant inductive kickback may be found. Terminal strips are also provided for input and output signals and power.


Please note that the #1 cause of problems for evaluation kit users is not reading and following the directions (all of them). The #2 cause of problems is poor solder joints (cold or bridging). Don’t become a statistic. ✔ each step.

Refer to the Illustrated Parts List for the components mentioned in the assembly steps. Note that some heavy PCB copper planes and some heavy component leads are soldered in this
kit. This may require a larger soldering iron tip and/or higher soldering iron temperatures than might normally be used. These steps are marked with an asterisk (*). Refer to the Illustrated Parts List for the components mentioned in each assembly step.

1. Notice that the printed circuit board (PCB) is labeled on one side as the “DUT SIDE” and the other side as “CIRCUIT” side.

2. As shown in the illustrated parts list, one or more of PAD’s accessory cage jack strip CJS01 was used in the assembly of this kit. It may be advisable to use the cage jack strips in your production circuit board as well. The CJS01 cage jack sockets provide a convenient and inexpensive socket.
Soldering and/or de-soldering the amplifier from the circuit board can be extremely difficult due to the high thermal conductivity of the amplifier’s pins and substrate. You can find the datasheet for the CJS01 on the PAD website under the “Accessory Modules” tab.

Assembled EVAL129 with amplifier mounted.
Optional accessory modules PAD125, PAD132 and
PAD131 also shown.

3. Refer to “Jumper Selection” below the Circuit
Diagram for the EVAL129 on page 4. Read all the options for the jumpers you will need installed or removed. Note that the kit comes wired with options 2 and 3. Install or remove jumpers as required at the locations indicated depending on the options you have chosen. Refer to the data
sheet for the PAD125 for complete information on current limit options. Refer to the data sheet for the PAD130 or PAD132 for details on its operation and applications.

4.* This step may require a soldering temperature higher than normal and/or a larger soldering iron tip. Three current limiting sense resistors, RS, are provided; one 0.005 Ω, one 0.010 Ω and one 0.015 Ω. Refer to the data sheet for the current limit module to determine which resistor value best fits your application (if you have chosen not to use the
current limit module select the 0.005 Ω resistor or install a length of heavy buss wire into the outer two holes at the location for the sense resistor RS). Smear a small amount of heat sink grease on the back of the selected resistor and then attach the resistor to heat sink HS1 at RS with a 4-40 X ½”
screw and nut. The plastic nut driver supplied with this kit will help here. Tighten the 4-40 resistor mounting hardware. Solder the resistor from the “CIRCUIT SIDE” of the PCB making sure that the holes are completely filled with solder.

5. D3 and D5 are transient voltage suppressor diodes and are not supplied since the type (breakdown voltage) varies with the application. They are not necessary for every application. They are most commonly used in application circuits where kickback from the load may force the supply
voltage above the limits of the amplifier.


6. The evaluation kit PCB can be mounted in several ways:

Option 1- Chassis mount. Use #6 x 1/4” M/F hex standoffs, and #6 nut (neither supplied) attached to the PCB at the four corners of the PCB and the chassis. Use another similar standoff at the center area where the amplifier is mounted.

Option 2- Bench-top mount. Use the five rubber bumpers supplied. These are “stick-on” components. Remove the release paper from each bumper and apply the bumper to the square outlines on the “CIRCUIT SIDE” of the PCB.

Option 3- DIN rail mount. The PCB can be mounted to either 1 or 2 DIN rails. For mounting the PCB to one DIN rail press the adaptors into the PCB in the holes at the edges of the PCB at locations 1 and 2 from the “CIRCUIT SIDE” of the PCB. Make sure that the plastic tines have fully spread out on the “DUT SIDE” of the PCB. If mounting to 2 DIN rails is desired, mount DIN rail adaptors at locations 3, 4, 5 and 6 in a similar manner. The center to center dimension of the DIN rails is to be 2.00” [50.8mm].

7. Components for locations R1-R7, D1, D2 are for the optional fold-over current limiting and are not supplied. Refer to the datasheet of the amplifier to find out how to apply circuits that require these components.

8. Remove the 4 hex nuts from the mounting spacers of the amplifier.

9. Align the 4 studs of the mounting spacers with the mounting holes in the PCB. Be sure that the amplifier’s pin 1 aligns with pin 1 on the PCB. Slowly lower the amplifier into the PCB, making sure that the pins of the amplifier and the cage jacks mate. Push the amplifier into the PCB until the mounting spacers meet the PCB.

10. Fasten the amplifier to the PCB with the 4 hex nuts previously removed. Do not over-tighten the nuts as this may strip the mounting studs. The provided plastic nut starter can assist you here.

11. If necessary, strip 1/8” of insulation from the wires connected to the fan. Twist and tin the wire ends. Insert the red wire into the cage jack labeled “+” and the black or blue wire into the jack marked “─” at the location marked “FAN”. Or, if you plan to use the PAD131 Fan Controller Accessory Module,
insert the fan wires similarly into the “+” and “─” cage jacks at the location marked “Fan Control”. Do not solder the fan wires into the PCB.

12. Add components as necessary to evaluate your application circuit. You can utilize the evaluation kit schematic and PCB views to map out your circuit and components. Remember, if you are using the current limit accessory module additional components or jumpers will be needed to program the operation of the module. See the PAD125 datasheet.

13. Connections for R8 and R9 (see the schematic of the evaluation board) are for building a Howland Current Pump (a transconductance circuit). See application note AN-42 Using Evaluation Kits to Implement Current Source Circuits available on the web site under the Application Notes tab.

14. The amplifier must be compensated to operate correctly. See the amplifier datasheet on Page 4 under PHASE COMPENSATION. Your selected phase compensation capacitor will be installed at “CC” on the evaluation kit PCB. A 470pF compensation capacitor has been installed but this may not be the best value for your application. If another value is better remove and replace CC as necessary. The kit also includes a 100pF capacitor.
CC must be a 200V rated capacitor and temperature stable, for example an NPO or X7R type.

15. If you have chosen to use the current limit module and/or power supply accessory module and PAD131 fan controller module install them at this time making sure that pin 1 on each module is aligned with the pin 1 marking on the PCB. The heat sink tabs on the PAD130 or PAD132 may be soldered to the PCB.

16. The evaluation kit assembly is complete. Be sure you have read and followed all the assembly steps. Do not forget any jumpers that need to be installed. Inspect the circuit board for solder shorts or poor solder joints. An illuminated magnifier is helpful.

17. Before applying power to your circuit set the power supply for ±20V and set the power supply current limit to approximately 100mA. Use little or no load at first. Apply an input signal and check the output with an oscilloscope to verify proper functionality. This step can prevent damaging the amplifier or the circuit board should there be some mistake in assembly. If you have chosen to build the Howland Current Pump make sure that the amplifier setup has the voltage compliance range needed for the load you have chosen.


Note that amplifier and accessory modules are purchased separately.



Note that options 2 and 3 are the default options.

Option 1. When using the PAD130 or PAD132 do not install jumpers J4,5.
This applies whether or not the current limit module PAD125 is installed.

Option 2. When not using the PAD130 or PAD132 do install jumpers J4,5.
This applies whether or not the current limit module PAD125 is installed. The kit comes wired with this option.

Option 3. To use the amplifier and current limit module together without fold-over current limit insert jumpers J1, 3.
This applies whether or not the PAD130 or PAD132 is installed. The kit comes wired with this option.

Option 4. To use the amplifier and current limit module together with fold-over current limit insert jumper J2.
This applies whether or not the PAD130 or PAD132 is installed.





Assembled EVAL129 with amplifier installed Optional accessory modules also shown