Datasheet

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Conclusion
Programming the TPS70102 Adjustable LDO Converter
R1 

V
O
V
ref
1

 R2
(1)
OUTPUT VOLTAGE
PROGRAMMING GUIDE
V
O
V
I
OUT
FB
R1
R2
GND
EN
IN
<0.5V
>2.7 V
TPS70102
0.1 µF
+
OUTPUT
VOLTAGE
R1 R2
2.5 V
3.3 V
3.6 V
UNIT
174
287
324
169
169
169
kΩ
kΩ
kΩ
Regulator Protection
TPS70145, TPS70148
TPS70151, TPS70158
TPS70102
SLVS222D – DECEMBER 1999 – REVISED NOVEMBER 2004
The figure 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 TPS70102 adjustable regulators are programmed using external resistor dividers as
shown in Figure 50 .
Resistors R1 and R2 should be chosen for approximately 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 = 30.1k Ω to set the divider current at approximately 50µA, and then calculate R1 using Equation 1 :
where:
• V
REF
= 1.224V typ (the internal reference voltage)
Figure 50. TPS70102 Adjustable LDO Regulator Programming
Both TPS701xx PMOS-pass transistors have built-in back diodes that conduct reverse currents when the input
voltage drops below the output voltage (for example, during power-down). Current is conducted from the output
to the input and is not internally limited. When extended reverse voltage is anticipated, external limiting may be
appropriate.
The TPS701xx also features internal current limiting and thermal protection. During normal operation, the
TPS701xx regulator 1 limits output current to approximately 1.6A (typ) and regulator 2 limits output current to
approximately 750mA (typ). When current limiting engages, the output voltage scales back linearly until the
overcurrent condition ends. While current limiting is designed to prevent gross device failure, care should be
taken not to exceed the power dissipation ratings of the package. If the temperature of the device exceeds 150 ° C
(typ), thermal-protection circuitry shuts it down. Once the device has cooled below 130 ° C (typ), regulator
operation resumes.
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