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which degrades SNR of the total system. If the ESR of the capacitor is not enough, then an additional resistor

must be added in series with the output capacitor. A capacitance of 1μF can connect to the NR pin to reduce

band-gap noise of the REF50xx.

Table 9-1 shows SNR measurements using different RC filters at the output of the OPA365, different values of

output capacitor for the REF50xx and different values of capacitors at the TRIM/NR pin.

Table 9-1. Data Acquisition Measurement Results for Different Conditions

TEST CONDITION 1

TEST CONDITION 2

OPA365 RC filter

124Ω, 1nF

REF5040 output capacitor

10μF

10μF + 47μF

TRIM/NR pin capacitor

0μF

1μF

SNR

86.7dB

92.8dB

9.2.1.3 Application Curve

Figure 9-2. FFT Plot-Noise Floor of Data Acquisition System

9.3 Power Supply Recommendations

The REF50xx family of voltage references features extremely low dropout voltage. With the exception of the

REF5020, which has a minimum supply requirement of 2.7V, the REF50xx family of voltage references operates

with a supply of 200mV more than the output voltage in an unloaded condition. For loaded conditions, Figure 6-6

provides a typical dropout voltage versus load plot. TI recommends a supply bypass capacitor ranging from 1μF

to 50μF for REF50xxI and REF50xxAI. TI recommends a supply bypass capacitor ranging from 1μF to 100μF for

REF50xxEI.

9.4 Layout

9.4.1 Layout Guidelines

9.4.1.1 REF50xxI, REF50xxAI Layout Guidelines

• Place the power-supply bypass capacitor as closely as possible to the supply and ground pins. The

recommended value of this bypass capacitor is from 1μF to 10μF. If necessary, add decoupling capacitance

to compensate for noisy or high-impedance power supplies.

• Place a 1μF noise filtering capacitor between the NR pin and ground.

• Verify that the output decouples with a 1μF to 50μF capacitor. A resistor in series with the output capacitor is

optional. For better noise performance, the recommended ESR on the output capacitor is from 1Ω to 1.5Ω.

www.ti.com

REF50, REF50E

SBOS410O – JUNE 2007 – REVISED OCTOBER 2025

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