TPS70102PWPR datasheet(32/42 Pages) TI

32 / 42 page

ESR 1

ESR 2

ESR 3

R1 +

ref

TPS70145, TPS70148

TPS70151, TPS70158

TPS70102

SLVS222I – DECEMBER 1999 – REVISED AUGUST 2010

www.ti.com

Figure 49. Correlation of Different ESRs and Their Influence on the Regulation of VO at a Load Step from

Low-to-High Output Current

Figure 49 also shows the impact of different ESRs on the output voltage. The left brackets show different levels

of ESRs where number 1 displays the lowest and number 3 displays the highest ESR.

From above, the following conclusions can be drawn:

•

The higher the ESR, the larger the droop at the beginning of load transient.

•

The smaller the output capacitor, the faster the discharge time and the greater the voltage droop during the

LDO response period.

Conclusion

To minimize the transient output droop, capacitors must have a low ESR and be large enough to support the

minimum output voltage requirement.

Programming the TPS70102 Adjustable LDO Converter

The output voltage of the TPS70102 adjustable regulators are programmed using external resistor dividers as

shown in Figure 50.

Resistors R1 and R2 should be chosen for approximately 50mA divider current. Lower value resistors can be

used, but offer no inherent advantage and waste more power. Higher values should be avoided as leakage

currents at the sense terminal increase the output voltage error. The recommended design procedure is to

choose R2 = 30.1k

Ω to set the divider current at approximately 50mA, and then calculate R1 using Equation 1:

(1)

where:

•

VREF = 1.224V typ (the internal reference voltage)

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