SLVS351Q September 2002 – June 2025 TPS796
PRODUCTION DATA
The internal voltage reference is a key source of noise in an LDO regulator. The TPS796 (legacy chip) has a noise-reduction (NR) pin that is connected to the voltage reference through a 250-kΩ internal resistor. The 250-kΩ internal resistor, in conjunction with an external bypass capacitor connected to the NR pin, creates a low-pass filter to reduce the voltage reference noise and, therefore, the noise at the regulator output. For the regulator to operate properly, the current flow out of the NR pin must be at a minimum, because any leakage current creates an IR drop across the internal resistor, thus creating an output error. Therefore, the bypass capacitor must have minimal leakage current. The bypass capacitor should be no more than 0.1 μF to make sure the capacitor is fully charged during the quick-start time provided by the internal switch shown in the functional block diagram of the legacy chip Figure 6-2. The output starts up slower as the bypass capacitance increases due to the RC time constant at the bypass pin that is created by the internal 250-kΩ resistor and external capacitor.