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To showcase how TPSM8A29 offers better transient performance than its fixed frequency counterpart (TPS543B20), both devices were set up using the same external components.
Initial Design | TPSM8A29 | TPS543B20 |
---|---|---|
Output Voltage | 0.9 V | 0.9 V |
Switching Frequency | 600 kHz | 500 kHz |
Input Capacitance | 330-µF + 4 x 22-µF | 330-µF + 4 x 22-µF |
Inductor | 0.6 µH (integrated) | 0.6 µH |
Output Capacitance | 2 x 100-µF | 2 x 100-µF |
Load Transient | 5 A - 13 A, at 4 A/µs step | 5 A - 13 A, at 4 A/µs step |
Transient Voltage pk-pk | 84 mV | 114 mV |
One difference to note here is that the TPSM8A29 module switching frequency setting is 600 kHz and is measured at 614 kHz, whereas The TPS543B20 converter switching frequency setting is 500 kHz and is measured at 550 kHz.
During the load transient, the TPSM8A29 achieves an 84 mV peak-to-peak voltage transient with only 42 mV zero-to-peak (Figure 2-1) during the unload transient. The DCAP-3 control architecture featured in TPSM8A29 allows for a higher crossover frequency and lower overall output capacitance. Additionally, when the load is turned off, TPSM8A29 does not begin switching until the entire load has dropped to zero, minimizing the peak voltage to 40 mV.
By contrast, notice that TPS543B20 is not stable with 2 x 100-µF (Figure 2-2), and the superfluous switching during the unload step resulted in the zero-to-peak transient of 60 mV. This output is 20 mV higher than TPSM8A29 at the same position.
When the design was iterated to improve and the transient performance, increasing output capacitance to 3 x 100-µF finally allowed the TPS543B20 to achieve loop stability, but the load transient performance of -53 mV and +45 mV (Figure 2-3), with a total of 98 mV peak-to-peak was still greater than the TPSM8A29 with 2 x 100-µF.
Per the results of the demonstration, the D-CAP3 control topology featured in TPSM8A29 enables the device to achieve loop stability with fewer output caps, reducing overall solution size in comparison to a similarly rated fixed frequency solution while maximizing load transient performance.
TPSM8A29 | TPS543B20 | |
---|---|---|
Output Capacitance | 2 x 100-µF | 3 x 100-µF |
Load Step-up | 43 mV | 53 mV |
Load Step-down | 41 mV | 45 mV |
Total pk-pk Voltage | 84 mV | 98 mV |