REF5040MDREP datasheet(15/29 Pages) TI1

15 / 29 page

ESR

2 • (R ESR) • C

2 • ESR • C

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

www.ti.com

SBOS471B – APRIL 2010 – REVISED JUNE 2015

Typical Applications (continued)

Figure 29. REF50xx FFT Plot of the Noise

With 10-µF Load Capacitor and 10-µ

Ω ESR

Every capacitor can be represented with a complicated equivalent model, which is voltage and frequency

dependent with a large number of passive components. For the purposes of this design, this model is limited to

the few components. The biggest impact on the creation of the low-pass filter and stability analysis is the

simplified model of equivalent series inductance and resistance. Considering good layout practice and inherently

low equivalent series inductance of today’s components, this model in the future analysis will be presented only

by equivalent capacitance and series resistance.

Figure 30. Equivalent SCH Of REF50xx With Load Capacitor for Stability Analysis

When evaluating the impact of ESR and CL on the performance the reference voltage, it is important to include

the effect of the open-loop output resistance (RO) of the output amplifier. The combination of RO, ESR, and CL

modifies the open-loop response curve by introducing one pole (fP) and one zero (fZ). The values RO, ESR, and

CL determine the corner frequency of the added pole fP; and the values of ESR and CL determine the corner

frequency of the added zero.

The introduction of the external ESR-CL on the output of the reference voltage modifies the output amplifier

open-loop gain curve. The added pole modifies the open-loop gain curve of the reference voltage output amplifier

by introducing a –20 dB/decade change at the frequency fP to the already –20 dB/decade slope of the open-loop

gain curve, making the slope equal to –40 dB/decade. The added zero at frequency fZ changes the open-loop

gain curve back to –20 dB/decade.

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REF5040MDREP Datasheet(PDF) 15 Page - Texas Instruments