SLUAA54B May   2020  – May 2021 TPS51206 , TPS51215A , TPS51220A , TPS51285A , TPS51396A , TPS51716 , TPS543B20 , TPS54424 , TPS54824 , TPS54A24 , TPS65295 , TPS82130 , TPS82140 , TPS82150 , TPSM41615 , TPSM41625 , TPSM84824


  1.   Trademarks
  2. 1Suggested Tiger Lake Point-of-Load Solutions
  3. 2Light Load Efficiency (Eco-Mode™) and Low Quiescent Current (ULQ™)
  4. 3Voltage Identification (VID) Capability with TPS51215A
  5. 4Fast Load Transient Response with D-CAP3™ and D-CAP2™ Control
  6. 5Small IC Packaging
  7. 6Conclusion
  8. 7Resources
  9. 8Revision History

Fast Load Transient Response with D-CAP3™ and D-CAP2™ Control

Since the load profile can change dramatically in industrial PC applications, it is important to consider AC transient performance. Choosing a DC/DC converter with a fast transient response using non-linear control techniques, such as constant on-time or D-CAP3, allows a fast transient response with minimal output capacitance. A converter using D-CAP3 control mode has three primary considerations for deciding the value of the output capacitance: transient (which includes load step and slew rate of the load step), output ripple, and stability. In applications where the load transient is stringent, the output capacitance is predominantly driven by the transient requirement. For a D-CAP3 based design, there is a minimum capacitance requirement in terms of small signal stability. This requirement prevents subharmonic, multiple-pulsing behavior in the modulator. Figure 4-1 shows the transient performance of the 8-A TPS51395 with a 5-V output, less than 100mV overshoot, and less than a 30µs recovery with output capacitance of 0.1 µF and 4x22 µF. The 0.8-A to 7.2-A load step has a slew rate of 2.5-A/µs.

GUID-99F5ADAC-59E1-484B-8D34-49A60F853B61-low.jpg Figure 4-1 TPS51395 Transient Waveform

The TPS51215A supplying VCCIN_AUX features adaptive on-time D-CAP2 control allowing ceramic output capacitors and acheives a fast load transient response shown in Figure 4-2 under the noted conditions below the waveform. The over-voltage and under-voltage test results also meet the target design specification, and the results are shown in Table 4-1 under the same conditions as the TPS51215A load transient waveform. The TPS51215A waveform conditions are VIN=12.6V, slew rate=12A/µs, FSW =600kΩ, L=0.22µH, and COUT=220µF + 22*12µF .

GUID-5FECA112-C436-4F43-8D51-78416B0F13B7-low.jpg Figure 4-2 TPS51215A Load Transient Waveform
Table 4-1 TPS51215A Load Transient Test Results
Voltage Rail Type Load Transient Validation Result (V) Target (V)
1.8V Undershoot 0A to 16A 1.67 1.62
Overshoot 16A to 0A 1.858 1.89
1.8V Undershoot 17A to 29A 1.678 1.62
Overshoot 29A to 17A 1.882 1.89