Datasheet

TPS72201, TPS72215
TPS72216, TPS72218
SLVS390B – DECEMBER 2001 – REVISED MAY 2002
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7
APPLICATION INFORMATION
The TPS722xx family of low-dropout (LDO) regulators functions with a very low input voltage (>1.8 V). The dropout voltage
is typically 50 mV at full load. Typical quiescent current (ground pin current) is only 85 µA and drops to 1 µA in the shutdown
mode.
DEVICE OPERATION
The TPS722xx 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 16.
NC
OUT
1
3
IN
EN
GND
2
4
5
V
I
V
O
0.1 µF
+
TPS722xx
0.1 µF
Figure 16. Typical Application Circuit
DUAL SUPPLY APPLICATION
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 17, 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.