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Programming the TPS70802 Adjustable LDO Regulator
R1=
V
V
OUT
REF
- 1
´ R2
( (
(1)
OUTPUTVOLTAGE
PROGRAMMINGGUIDE
V
O
V
I
OUT
FB
R1
R2
GND
EN
IN
<0.7V
>2.0 V
TPS70802
0.1 mF
+
OUTPUT
VOLTAGE
R1 R2
2.5V
3.3V
3.6V
UNIT
31.6
51.1
59.0
30.1
30.1
30.1
kW
kW
kW
Regulator Protection
TPS70845, TPS70848
TPS70851, TPS70858
TPS70802
SLVS301D – JUNE 2000 – REVISED DECEMBER 2007
The output voltage of the TPS70802 adjustable regulators is programmed using external resistor dividers as
shown in Figure 40 .
Resistors R1 and R2 should be chosen for approximately a 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 = 30.1 k Ω to set the divider current at approximately 50 µ A, and then calculate R1 using Equation 1 :
where:
• V
REF
= 1.224 V typ (the internal reference voltage)
Figure 40. TPS70802 Adjustable LDO Regulator Programming
Both TPS708xx 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 TPS708xx also features internal current limiting and thermal protection. During normal operation, the
TPS708xx regulator 1 limits output current to approximately 1.6 A (typ) and regulator 2 limits output current to
approximately 750 mA (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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