NC

V

IN

TEMP

GND

REF5040

1

8

NC

Variable

+4.096V

C

1µF - 50µF

OUT

+5V

C

10µF

IN

2

3

4

NC

V

OUT

TRIM

7

6

5

REF5020-EP, REF5025-EP, REF5040-EP, REF5050-EP

SBOS471B – APRIL 2010 – REVISED JUNE 2015

www.ti.com

Typical Applications (continued)

8.2.1.3 Application Curves

Figure 26. Noise Measurements of Properly Design

Figure 27. FFT of Data Acquisition System Design With

REF50xx Data Acquisition System from Figure 33

REF50xx from Figure 33

8.2.2 Positive Reference Voltage

Figure 28. REF50xx With Load Capacitor

8.2.2.1 Detailed Design Procedure

8.2.2.1.1

Load Capacitance

To determine how much noise the reference voltage is contributing in a real application, this design uses the

circuit presented in Figure 28. For the same conditions as power supply, input decoupling, and load current,

measure the output noise for different output decoupling or load capacitors. The load capacitor type will change

the low-pass filter frequency that is created on the output. This filter is determined by an added capacitor value

and two parasitic components: the open-loop output impedance of the internal amplifier to the reference voltage,

and the ESR of the external capacitor.

Figure 29 shows a fast-Fourier-transform (FFT) plot of the output signal of the reference voltage circuit with a 10-

μF ceramic capacitor load. The output noise level peaks at around 9 kHz because of the response of the internal

This peaking is the main contributor to the overall measured noise. This output noise, measured with an analog

meter over a frequency range of up to 80 kHz, is approximately 16.5

μVRMS. If the voltage-reference circuit was

connected to the input of an ADC, the measured noise across a 65-kHz frequency range would be 138

μVPP.

This noise level makes this solution adequate for 8- to 14-bit converters.

14

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