Datasheet

TPS78825, TPS78833
SLVS382A – JUNE 2001 – REVISED JULY 2001
6
www.ti.com
APPLICATION INFORMATION
The TPS788xx family of low-dropout (LDO) regulators has been optimized for use in battery-operated
equipment. It features extremely low dropout voltages, low output noise, low quiescent current (17 µA typically),
and enable inputs to reduce supply currents to 1 µA when the regulator is turned off. A typical application circuit
is shown in Figure 15.
1 µF
SR
OUT
1
3
IN
EN
GND
2
4
5
V
I
ESR = 0.2 Ω
V
O
4.7 µF
+
0.01 µF
Figure 15. 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 TPS788xx, 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 TPS788xx 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.
CAPACITOR SELECTION
PART NO. MFR. VALUE MAX ESR
†
SIZE (H × L × W)
†
T494B475K016AS Kemet 4.7 µF 1.5 Ω 1.9 × 3.5 × 2.8
195D106x0016x2T Sprague 10 µF 1.5 Ω 1.3 × 7.0 × 2.7
695D106x003562T Sprague 10 µF 1.3 Ω 2.5 × 7.6 × 2.5
TPSC475K035R0600 AVX 4.7 µF 0.6 Ω 2.6 × 6.0 × 3.2
†
Size is in mm. The ESR maximum resistance is in Ohms at 100 kHz and T
A
= 25°C. Contact the
manufacturer for the minimum ESR values.