SBOA618 December   2025 TMCS1126

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Current Ratings and Thermal
    1. 2.1 Current Ratings
    2. 2.2 Effects of PCB and Layout
  6. 3Accuracy
  7. 4Bandwidth, Response Time and Propagation Delay
    1. 4.1 Bandwidth
    2. 4.2 Response Time
    3. 4.3 Propagation Delay
  8. 5Lightning and Surge
    1. 5.1 Knowing Lighting and SPD in Solar
    2. 5.2 Understanding IEC 61643-32
    3. 5.3 Understanding IEC 61643-11
    4. 5.4 Surge Requirements in Solar Systems
    5. 5.5 Challenges and Designs for In-Package Hall Sensor
  9. 6Isolation and Reliability
  10. 7Summary
  11. 8References

4.1 Bandwidth

Bandwidth is defined as the cutoff frequency at -3dB gain, as shown in Figure 4-1. For example, TMCS1123 has -3dB gain at 250kHz. When measuring peak or valley current values, a high enough bandwidth is needed, because a triangular current waveform can be decomposed into a superposition of many sine waves of different frequencies. In this case, it is important to make sure high frequency harmonics are not attenuated, so that the real value and measured peak or valley current has minimal error.

Analog Signal Bandwidth Figure 4-1 Analog Signal Bandwidth

In digital controlled switch mode converters, normally, the control loop bandwidth is < 0.2×fsw (for simple analysis, considering fsample = fsw), because of the requirement for an accurate state-space average model and low phase delay within the control loop bandwidth.

The sensing stage of a current sensor can be modeled as a first-order low-pass filter. The transfer function is shown in equation (1), BW is the bandwidth of the current sensor. So, a lower bandwidth brings a bigger phase lag and amplitude attenuation at high frequency.

Equation 1. Glpf=1τs+1,τ=12π×BW

The three scenarios discussed below are discussed regarding the bandwidth topic. Control loop bandwidth is the digital control bandwidth of the system, not the Hall sensor's bandwidth.

For solar inverters or PCS, the switching frequency is normally below 50kHz (for simple analysis, considering fsample=fsw), so the control loop bandwidth is normally below 10kHz. According to Equation 1 , a 250kHz bandwidth current sensor at 10kHz brings approximately a 2° phase delay in the control loop, which is almost negligible.

For module level power electronics (MLPE), in which the third-generation power semiconductor devices, such as gallium nitride (GaN), are becoming increasingly popular. The switching frequency can be up to 400kHz. Depending on the sampling frequency and control loop execution frequency, the bandwidth of the control loop can also be very high. The phase delay for a 250kHz current sensor TMCS1123 at 50kHz can be approximately 11°, so a higher bandwidth current sensor such as TMCS1126, TMCS1133 can be used to reduce the phase delay.

Normally, it is required that the bandwidth of hall sensors must be 5 to 10 times higher than the switching frequency to achieve accurate current sensing.

For over-current protection (OCP), the overcurrent condition can be regarded as a step input. If the bandwidth is too low, high frequency components in the step input are attenuated. So, the amplitude of current sensor output can be lower than that of the original input at the beginning of over-current event, causing obvious OCP delay which is dangerous for the protection of the power device. Of course, response time (Tr) and propagation delay (Tpd) also play an important role in OCP event, which is discussed in following sections.