Datasheet

C1
1 µF
FB
OUT
1
3
IN
EN
GND
2
4
5
V
I
ESR = 0.2 Ω
V
O
4.7µF
+
TPS76901
TPS76901-EP
www.ti.com SLVSA53A –NOVEMBER 2009–REVISED DECEMBER 2009
APPLICATION INFORMATION
(1)
The TPS76901 low-dropout (LDO) regulator has been optimized for use in battery-operated equipment. It
features extremely low dropout voltages, low quiescent current (17 μA nominally), and enables inputs to reduce
supply currents to 1 μA when the regulators are turned off.
DEVICE OPERATION
The TPS76901 uses a PMOS pass element to dramatically reduce both dropout voltage and supply current over
more conventional PNP-pass-element LDO designs. The PMOS pass element is a voltage-controlled device and,
unlike a PNP transistor, it does not require increased drive current as output current increases. Supply current in
the TPS76901 is essentially constant from no load to maximum load.
Current limiting prevents damage by excessive output current. 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
PMOS pass element includes a back gate diode that conducts reverse current when the input voltage level drops
below the output voltage level.
A voltage of 1.7 V or greater on the EN input will disable the TPS76901 internal circuitry, reducing the supply
current to 1 μA. A voltage of less than 0.9 V on the EN input will enable the TPS76901 and will enable normal
operation to resume. The EN input does not include any deliberate hysteresis, and it exhibits an actual switching
threshold of approximately 1.5 V.
A typical application circuit is shown in Figure 5.
Figure 5. Typical Application Circuit
EXTERNAL CAPACITOR REQUIREMENTS
Although not required, a 0.047-μF or larger ceramic input bypass capacitor, connected between IN and GND and
located close to the TPS76901, is recommended to improve transient response and noise rejection. A
higher-value electrolytic input capacitor may be necessary if large, fast-rise-time load transients are anticipated
and the device is located several inches from the power source.
Like all low dropout regulators, the TPS76901 requires an output capacitor connected between OUT and GND to
stabilize the internal control loop. The minimum recommended capacitance is 4.7 μF. The ESR (equivalent series
resistance) of the capacitor should be between 0.2 Ω and 10 Ω. to ensure stability. Capacitor values larger than
4.7 μF are acceptable, and allow the use of smaller ESR values. Capacitances less than 4.7 μF are not
recommended because they require careful selection of ESR to ensure stability. Solid tantalum electrolytic,
aluminum electrolytic, and multilayer ceramic capacitors are all suitable, provided they meet the requirements
described above. Most of the commercially available 4.7-μF surface-mount solid tantalum capacitors, including
devices from Sprague, Kemet, and Nichico, meet the ESR requirements stated above. Multilayer ceramic
capacitors may have very small equivalent series resistances and may thus require the addition of a low value
series resistor to ensure stability.
(1) Application information is provided for commercial temperature as a reference and not for high temperature.
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Product Folder Link(s): TPS76901-EP