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ESR 1
ESR 2
ESR 3
3
1
2
t
1
t
2
I
O
V
O
Conclusion
Programming the TPS70702 Adjustable LDO Converter
R1 +
ǒ
V
O
V
ref
*1
Ǔ
R2
(1)
TPS70745, TPS70748
TPS70751, TPS70758
TPS70702
SLVS291D – MAY 2000 – REVISED DECEMBER 2007
Figure 45. Correlation of Different ESRs and Their Influence on the Regulation of V
O
at a Load Step from
Low-to-High Output Current
Figure 45 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.
To minimize the transient output droop, capacitors must have a low ESR and be large enough to support the
minimum output voltage requirement.
The output voltage of the TPS70702 adjustable regulators are programmed using external resistor dividers as
shown in Figure 46 .
Resistors R1 and R2 should be chosen for approximately 50 µ A 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 50 µ A, and then calculate R1 using Equation 1 :
where:
• V
REF
= 1.224V typ (the internal reference voltage)
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