SLYY222A November   2023  – November 2024 ADC12DJ5200RF , ADS127L11 , BQ79731-Q1 , REF35 , REF70 , TPS62912 , TPS62913 , TPS7A20 , TPS7A94 , TPSM82912 , TPSM82913

 

  1.   1
  2.   Overview
  3.   At a glance
  4.   Noise and ADCs
  5.   Defining noise and precision in a power architecture
  6.   Innovations in low-noise and low-power voltage references
  7.   Innovations in buried Zener voltage references
  8.   Innovations in ultra-low-noise voltage references
  9.   Improving noise and thermal performance with simplified power architectures
  10.   High-current low noise with LDO supply rails
  11.   Innovations in precision battery monitoring
  12.   Conclusion
  13.   Additional resources

High-current low noise with LDO supply rails

The biggest intrinsic noise source for an LDO is its internal voltage reference. In order to reduce noise and improve overall system performance, a variety of LDOs in the TI portfolio have incorporated a noise-reduction feature with a NR pin. Adding a capacitor (CNR/SS) to the NR pin creates a resistor-capacitor filter with internal resistance at the VREF node, as shown in Figure 16.

N-channel metal-oxide semiconductor LDO with an NR/SS pin. Figure 16 N-channel metal-oxide semiconductor LDO with an NR/SS pin.
A.
Equation 2. V O U T = V R E F   × 1 + R 1 R 2

Newer LDOs implement a highly accurate, high-precision and low-noise current source, followed by an error amplifier. Implementing a unity-gain configuration also ensures low noise over the entire output range. A great example of one of these high-accuracy low-noise LDOs is the TPS7A94, which can achieve 0.46 μVRMS over a 10-Hz to 100-kHz bandwidth. Figure 17 shows the output noise density and the impact of increasing CNR/SS from 1 µF to 10 µF.

Output noise vs. CNR/SS of the TPS7A94.
VOUT = 3.3 V CIN = COUT = 10 μF
IOUT = 500 mA 10 Hz ≤ fSW ≤100 kHz
Figure 17 Output noise vs. CNR/SS of the TPS7A94.

The combination of features that the TPS7A94 possesses represents a new generation of low-noise LDOs capable of achieving excellent voltage accuracy and ultra-low noise, which is important when the TPS7A94 is the primary power supply for a high-resolution signal chain, since higher-resolution ADCs are more sensitive to noise. In a typical application, shown in Figure 18, the TPS7A94 is the main power supply for the ADC, operational amplifier, clock and external voltage reference, which are high-performance devices. The goal of this signal chain is to minimize the total harmonic distortion, signal-to-noise ratio and gain error of the ADS127L11 by using the ultra-low input current noise with the low 1/f noise of the TPH210 and REF70. The low noise and high PSRR of the TPS7A94 provide a clean supply line that limits any noise that could couple into the active circuitry of the TPS210, ADC127L11 and REF70 and degrade performance.

TPS7A94 powering a signal chain. Figure 18 TPS7A94 powering a signal chain.