7.2.2.1 Output Noise

In most LDO regulators, the band gap is the dominant noise source. If a noise-reduction capacitor (C_NR) is used with the TPS735 device, the band gap does not contribute significantly to noise. Noise is dominated by the output resistor divider and the error-amplifier input. To minimize noise in a given application, use a 10-nF noise reduction capacitor. For the adjustable version, smaller value resistors in the output resistor divider reduce noise. A parallel combination that produces 2 μA of divider current has the same noise performance as a fixed voltage version with a C_NR. To further optimize noise, set the ESR of the output capacitor to approximately 0.2 Ω. This configuration maximizes phase margin in the control loop, which reduces the total output noise up to 10%. TI recommends a maximum capacitor value of 10 nF.

Equation 1 calculates the approximate integrated output noise from 10 Hz to 100 kHz with a C_NR value of
10 nF.

Equation 1.

The TPS735adjustable version does not have the noise-reduction pin available, so ultra-low noise operation is not possible. Noise is minimized according to the previously listed recommendations.