Relationship between Transient Response, Rise Time, and Slew Rates Settings

Using slew rates with gain bandwidth (GBW) programming can give you the flexibility to optimize the performance of your setup within necessary physical limitations. This ensures that the electronic load can work in a wide variety of use cases.

To optimize your system:
  1. Program the max slew rate into the system.
  2. Setup the system and DUT with the shortest possible cabling.
  3. Tune the system for the fastest possible rise time with minimal overshoots and ringing.
  4. Estimate the Max GBW limited slew rate for the setup using the following equation.

    80% * Current_Step_Amplitude / Rise_Time

    Note The maximum slew rate will change with the amplitude of the current step.
  5. Program the desired slew rate, which can be equal to or slower than the max GBW limited slew rate.

Assuming that your system is stable when programed with the maximum slew rate, setting a faster GBW (assuming system is still stable at the faster GBW) will result in a faster rise time and maximum slew rate. Even if you program a slew rate that is faster than the GBW limited slew rate, the system cannot physically achieve that faster rate.

Figure 17. Limitations on Slew Rates based on GBW


In order to increase the maximum attainable slew rates, you will need to increase the GBW. However, GBW cannot be increased indefinitely. It is limited by the stability of the system, including the electronic load, the cables, and any DUTs.

To reduce the slew rate, you can set a GBW lower than physically limited GBW. An issue with this method is that GBW actually determines rise time and not slew rates directly. Also, the amplitude of the step will determine the final slew rate numbers in A/us.

Effort is required to calculate the required slew rates from the GBW. Compensation settings or empirical experimentations will be necessary. Hence using the slew rate programming capability is recommended.

Figure 18. Optimizing the GBW


The slew rate programming capability will allow you to program a deterministic slew rate. As long as the programmed rate is slower than the fastest possible rate at the particular GBW settings, you will be able to obtain the exact slew rate that you desire.

When programming the slew rates, you can also have a different slew rate for the rising and falling of the step. In advanced sequences, it is possible to have unique and independent slew rates for each step in the sequence.