Table Of Contents

Examples of Determining Extended Range Pulse Parameters and Optimizing Slew Rate using NI SourceAdapt

Version:
    Last Modified: November 30, 2020

    spd-note-note
    Note  

    Specifications listed in examples are for demonstration purposes only and do not necessarily reflect specifications for this device.

    Example 1: Determining Extended Range Pulse On Time and Duty Cycle Parameters for the PXIe-4139 (40W)

    Determine the extended range pulsing parameters, assuming the following operating point.

    Output function Pulse Current
    Pulse voltage limit, Vpulse 40 V
    Pulse current level, Ipulse 6 A
    Bias voltage limit, Vbias 0.1 V
    Bias current level, Ibias 0 A
    Pulse on time, ton 1.5 ms
    Chassis' slot cooling capacity ≥58 W

    Solution

    Begin by calculating the pulse power using the following equation.

    Pulse power = V pulse * I pulse = 40 V *  6 A = 2 40 W

    For PXIe-4139 (40W), refer to the following figures to identify next steps. First, verify the the region of operation using Figure 1, which shows 240 W is in the extended range pulsing region.

    Next, refer to Figure 1, which shows the maximum pulse on time, ton, is limited by the maximum pulse energy, EpulseMax. Use the pulse energy equation (Equation 2) from Table 1 to calculate the maximum pulse on time, tonMax (Equation 6).

    t onMax = | E pulseMax V pulse * I pulse |      ( E q . 6 ) = | 0.4 J 40 V *  6 A | = 1.67 ms

    Next, refer to Figure 2, which shows the maximum duty cycle, D, is limited by the cycle average power, PCA.If the required pulse on time is 1.5 ms and the module is installed in a chassis with slot cooling capacity ≥58 W, use the cycle average power equation (Equation 5) from Table 1 to calculate the minimum pulse off time, toffMin (Equation 7).

    t offMin = | P CA * t on V pulse * I pulse * t on P CA V bias * I bias |      ( E q . 7 ) = | 40 W *  1.5 ms 40 V *  6 A *  1.5 ms 40 W 0.1 V *  0 A | = 7.5 ms

    Finally, verify that the pulse cycle time, tcycle, is greater than or equal to the minimum pulse cycle time, tcycleMin (5 ms). To calculate the pulse cycle time, use the following equation:

    t cycle = t on + t off     (Eq. 4) = 1.5 ms + 7.5 ms = 9 ms

    In this case, the pulse cycle time meets the minimum pulse cycle time specification.

    Therefore, a 40 V, 6 A pulse with an on time of 1.5 ms and a pulse off time of 7.5 ms is supported, since it fulfills the following criteria:

    • Greater than the minimum pulse on time of 10 μs
    • Equal to the minimum pulse off time of 7.5 ms to meet maximum cycle average power
    • Greater than the minimum pulse cycle time of 5 ms

    Example 2: Determining Extended Range Pulse On Time and Duty Cycle Parameters for the PXIe-4139 (20W)

    Determine the extended range pulsing parameters, assuming the following operating point.

    Output function Pulse Current
    Pulse voltage limit, Vpulse 40 V
    Pulse current level, Ipulse 6 A
    Bias voltage limit, Vbias 0.1 V
    Bias current level, Ibias 0 A
    Pulse on time, ton 1.5 ms
    Chassis' slot cooling capacity ≥58 W

    Solution

    Begin by calculating the pulse power using the following equation.

    Pulse power = V pulse * I pulse = 40 V *  6 A = 240 W

    Since the pulse power of 240 W is within the 500 W region of Figure 2, the maximum configurable on time is 400 μs and maximum duty cycle is 2%.

    For example, if the required pulse on time is 100 μs, and the required pulse cycle time is 10 ms, calculate the pulse off time and verify the duty cycle using the following equations.

    t off = t cycle t on = 10 ms 100 μ s = 9 .9 ms

    Duty cycle = t on t cycle *  100% = 1 %

    Therefore, a pulse with an on time of 100 μs and 1% duty cycle would be supported, since it fulfills the following criteria:

    • Greater than the minimum pulse on time of 50 μs
    • Less than the maximum pulse on time of 400 μs and duty cycle of 2%
    • Greater than the minimum pulse cycle time of 5 ms

    Example 3: Using NI SourceAdapt to Increase the Slew Rate of the Pulse

    Determine the appropriate operating parameters and custom transient response settings, assuming the following example parameters.

    Output function Pulse Current
    Pulse voltage limit, Vpulse 50 V
    Pulse current level, Ipulse 5 A
    Bias voltage limit, Vbias 0.1 V
    Bias current level, Ibias 0 A
    Transient response Fast
    Load, cable impedance 4.5 Ω, 40 μH
    Pulse on time, ton 10 μs
    Pulse off time, toff 4.99 ms

    The SMU Transient Response can be configured to three predefined settings, Slow, Normal, and Fast. If these settings do not provide the desired pulse response, a fourth setting, Custom, enables NI SourceAdapt[1] technology which provides the ability to customize the SMU response to any load, and achieve an ideal response with minimum rise times and no overshoots or oscillations.

    Figure 1. 10 μs Pulse Output with Load, Fast Transient Response

    Solution

    SourceAdapt allows users to set the desired gain bandwidth, compensation frequency, and pole-zero ratio through custom transient response to obtain the desired pulse waveform. To use SourceAdapt, first set the Transient Response to Custom.

    To achieve the resulting waveform in the following figure, use the parameters in the following table.

    Figure 2. 10 μs Pulse Output with Load, Custom Transient Response
    Transient response Custom
    Current: Gain bandwidth 260 kHz
    Current: Compensation frequency 140 kHz
    Current: Pole-zero ratio 0.75

    Gain bandwidth is directly proportional to the step response slew rate. The higher the gain bandwidth, the higher the slew rate. It is worth noting that increasing the gain bandwidth will likely increase ringing. However, this can likely be removed by appropriately setting the compensation frequency and the pole-zero ratio.

    Figure 3. Example of Ringing Frequency

    Compensation frequency and pole-zero ratio are used to determine the frequencies of the SMU control loop pole and zero, which can be used to optimize the system transient response by increasing phase margin and reducing ringing. To reduce the overshoot, it is recommended to set the compensation frequency close to the overshoot ringing frequency, see Fc in Figure 3, and set the pole-zero ratio to be greater than 1.

    For reference, the pole frequency and zero frequency are derived by the following equations.

    Pole frequency = Compensation frequency * Pole-zero ratio

    Zero frequency = Compensation frequency Pole-zero ratio

    These settings can be accessed through the Transient Response set to Custom: Voltage or Current.

    • 1 Visit ni.com for more information about NI SourceAdapt Next-Generation SMU Technology.

    Recently Viewed Topics