www.ti.com
TPS72101, TPS72115
TPS72116, TPS72118
SLVS352B 鈥?DECEMBER 2001 鈥?REVISED MAY 2002
APPLICATION INFORMATION
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
碌A
and drops to 1
碌A
in the shutdown
mode.
DEVICE OPERATION
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
碌A.
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掳C.
Recovery is automatic when the junction temperature drops approximately 20掳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.
TPS721xx
VI
0.1
碌F
3
EN
+
GND
2
0.1
碌F
NC
4
1
IN
OUT 5
VO
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
碌s)
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
