Datasheet

TPS71025
LOW-DROPOUT VOLTAGE REGULATOR
SLVS162A – MAY 1997 – REVISED MAY 1998
14
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
SENSE
OUT
OUT
9
8
6
10
IN
IN
IN
EN
GND
321
15
14
13
V
I
C1
0.1 µF
50 V
CSR
V
O
C
o
10 µF
+
TPS71025
†
†
Capacitor selection is nontrivial. See external capacitor requirements section.
Figure 19. Typical Application Circuit
The TPS71025 low-dropout (LDO) regulator overcomes many of the shortcomings of earlier-generation LDOs,
while adding features such as a power-saving shutdown mode.
device operation
The TPS71025, unlike many other LDOs, features very low quiescent current that remains virtually constant
even with varying loads. Conventional LDO regulators use a pnp-pass element, the base current of which is
directly proportional to the load current through the regulator (I
B
= I
C
/β). Examination of the data sheets reveals
that those devices are typically specified under near no-load conditions; actual operating currents are much
higher as evidenced by typical quiescent current versus load current curves. The TPS71025 uses a PMOS
transistor to pass current; because the gate of the PMOS element is voltage driven, operating currents are low
and stable over the full load range. The TPS71025 specifications reflect actual performance under load.
Another pitfall associated with the pnp-pass element is its tendency to saturate when the device goes into
dropout. The resulting drop in β forces an increase in I
B
to maintain the load. During power up, this translates
to large start-up currents. Systems with limited supply current may fail to start up. In battery-powered systems,
it means rapid battery discharge when the voltage decays below the minimum required for regulation. The
TPS71025 quiescent current remains low even when the regulator drops out, eliminating both problems.
The TPS71025 also features a shutdown mode that places the output in the high-impedance state (essentially
equal to the feedback-divider resistance) and reduces quiescent current to under 2 µA. If the shutdown feature
is not used, EN
should be tied to ground. Response to an enable transition is quick; regulated output voltage
is reestablished in typically 120 µs.
minimum load requirements
The TPS71025 family is stable even at zero load; no minimum load is required for operation.
SENSE-pin connection
The SENSE pin must be connected to the regulator output for proper functioning of the regulator. Normally, this
connection should be as short as possible; however, the connection can be made near a critical circuit (remote
sense) to improve performance at that point. Internally, SENSE connects to a high-impedance wide-bandwidth
amplifier through a resistor-divider network, and noise pickup feeds through to the regulator output. Routing the
SENSE connection to minimize/avoid noise pickup is essential. Adding an RC network between SENSE and
OUT to filter noise is not recommended because it can cause the regulator to oscillate.