Datasheet

ESR1
ESR2
ESR3
3
1
2
I
OUT
V
OUT
t
1
t
2
R1=
V
V
OUT
REF
- 1
´ R2
( (
TPS70245, TPS70248
TPS70251, TPS70258
TPS70202
www.ti.com SLVS286E –JUNE 2000–REVISED DECEMBER 2009
Figure 39. Correlation of Different ESRs and Their Influence on the Regulation of V
O
at a Load Step from
Low-to-High Output Current
Figure 39 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 the 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 TPS70202 Adjustable LDO Regulator
The output voltage of the TPS70202 adjustable regulators is programmed using external resistor dividers as
shown in Figure 40.
Resistors R1 and R2 should be chosen for approximately a 50μA 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 = 30.1kΩ to set the divider current at approximately 50μA, and then calculate R1 using Equation 1:
(1)
where:
• V
REF
= 1.224V typ (the internal reference voltage)
Copyright © 2000–2009, Texas Instruments Incorporated Submit Documentation Feedback 27