Feature: RF Design
Figure 7. LT8627SP with an active drooping resistor placed between OUTS and VC to achieve a fast transient recovery time.
Figure 8. Droop transient response can be achieved to minimise the transient recovery time for LT8627SP.
the transient. Te drooping voltage can be expressed as:
Whereas ∆VOUT is the initial voltage variation caused by the
load transient, ∆IOUT is the load transient current, and g is the VC pin to switch current gain. In designing the drooping circuit shown in Figure 7, special considerations need to be taken: • Te drooping current should not exceed the VC pin current limit. For LT8627SP’s error amplifier output, it is proper to limit the current to below 200µA to avoid saturation and this can be achieved by changing R7 and R8 values.
• Te drooping voltage needs to accommodate the output capacitance so that the voltage deviation during the transient is on a similar level of the drooping voltage to achieve minimum recovery time during the transient.
Figure 8 shows typical waveforms for the above-mentioned circuit during a 1A to 16A to 1A load transient. It is worth noticing that now the 16A to 1A load transient speed is no longer bottlenecked by the bandwidth but by the minimum on time of the regulator. Te wireless RF field is becoming increasingly calculation
dependent and sensitive to the transient response time due to the time critical nature of the high speed signal processing. System design engineers face challenges to increase the power supply transient response speed so that the blanking time can be minimised. Te Silent Switcher 3 family is the next-generation of monolithic regulators optimised for noise sensitive, intensive dynamic load transient solutions in wireless, industrial, defence and healthcare fields. Based on the load conditions, special techniques and circuits can be applied to further improve the transient response. Analog Devices:
www.analog.com
www.electronicsworld.co.uk February 2025 37
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