Datasheet

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APPLICATION INFORMATION
DEVICE OPERATION
NC
OUT
1
3
IN
EN
GND
2
4
5
V
I
V
O
0.1 µF
TPS721xx
0.1 µF
DUAL SUPPLY APPLICATION
TPS72101 , , TPS72115
TPS72116 , TPS72118
SLVS352C – DECEMBER 2001 – REVISED MARCH 2006
The TPS721xx family of low-dropout (LDO) regulators functions with a very low input voltage (>1.8 V). The
dropout voltage is typically 150 mV at full load. Typical quiescent current (ground pin current) is only 85 µA and
drops to 1 µA in the shutdown mode.
The TPS721xx family can be operated at low input voltages due to low voltage circuit design techniques and a
PMOS pass element that exhibits low dropout.
A logic low on the enable input, EN, shuts off the output and reduces the supply current to less than 1 µA. EN
may be tied to V
IN
in applications where the shutdown feature is not used.
Current limiting and thermal protection prevent damage by excessive output current and/or power dissipation.
The device switches into a constant-current mode at approximately 350 mA; further load reduces the output
voltage instead of increasing the output current. The thermal protection shuts the regulator off if the junction
temperature rises above 170°C. Recovery is automatic when the junction temperature drops approximately 20°C
below the high temperature trip point. The PMOS pass element includes a back diode that safely conducts
reverse current when the input voltage level drops below the output voltage level.
A typical application circuit is shown in Figure 18 .
Figure 18. Typical Application Circuit
In portable, battery-powered electronics, separate power rails for the DSP or microcontroller core voltage,
V
(CORE)
, and I/O peripherals (V
IO
) are usually necessary. The TPS721xx family of LDO linear regulators is ideal
for providing V
(CORE)
for the DSP or microcontroller. As shown in Figure 19 , two AAA batteries provide an input
voltage to a boost converter and the TPS72115 LDO linear regulator. The batteries combine input voltage ranges
from 3.0 V down to 1.8 V near the end of their useful lives. Therefore, a boost converter is necessary to provide
the typical 3.3 V needed for V
IO
, and the TPS72115 linear regulator provides a regulated V
(CORE)
voltage, which
in this example is 1.5 V. Although there is no explicit circuitry to perform power-up sequencing of first V
(CORE)
then V
IO
, the output of the linear regulator reaches its regulated voltage much faster (< 400 µs) than the output of
any switching type boost converter due to the inherent slow start up of those types of converters. Assuming a
boost converter with minimum V
I
of 1.8 V is appropriately chosen, this power supply solution can be used over
the entire life of the two off-the-shelf AAA batteries. Thus, this solution is very efficient and the design time and
overall cost of the solution is minimized.
7
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