JAJSRK1G March 2012 – November 2023 TPS7A7100
PRODUCTION DATA
As a result of the very fast transient response and low-dropout operation support, the line impedance must be reduced at the input pin of the TPS7A7100. The line impedance depends heavily on various factors, such as wire (PCB trace) resistance, wire inductance, and output impedance of the upstream voltage supply (power supply to the TPS7A7100). Therefore, a specific value for the input capacitance cannot be recommended until the previously listed factors are finalized.
In addition, simple usage of large input capacitance can form an unwanted LC resonance in combination with input wire inductance. For example, a 5-nH inductor and a 10-µF input capacitor form an LC filter that has a resonance at 712 kHz. This value of 712 kHz is well inside the bandwidth of the TPS7A7100 control loop.
The best guideline is to use a capacitor of up to 1 µF with well-designed wire connections (PCB layout) to the upstream supply. If optimizing the input line is difficult, use a large tantalum capacitor in combination with a good-quality, low-ESR, 1-µF ceramic capacitor.