Datasheet
SLVS293D − NOVEMBER 2000 − REVISED MAY 2002
20
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
input capacitor
For a typical application, a ceramic input bypass capacitor (0.22 µF−1 µF) is recommended to ensure device
stability. This capacitor should be as close as possible to the input pin. Due to the impedance of the input supply,
large transient currents will cause the input voltage to droop. If this droop causes the input voltage to drop below
the UVLO threshold, the device will turn off. Therefore, it is recommended that a larger capacitor be placed in
parallel with the ceramic bypass capacitor at the regulator’s input. The size of this capacitor depends on the
output current, response time of the main power supply, and the main power supply’s distance to the regulator.
At a minimum, the capacitor should be sized to ensure that the input voltage does not drop below the minimum
UVLO threshold voltage during normal operating conditions.
output capacitor
As with most LDO regulators, the TPS755xx requires an output capacitor connected between OUT and GND
to stabilize the internal control loop. The minimum recommended capacitance value is 47 µF with an ESR
(equivalent series resistance) of at least 200 mΩ. As shown in Figure 29, most capacitor and ESR combinations
with a product of 47e−6 x 0.2 = 9.4e−6 or larger will be stable, provided the capacitor value is at least 47 µF.
Solid tantalum electrolytic and aluminum electrolytic capacitors are all suitable, provided they meet the
requirements described in this section. Larger capacitors provide a wider range of stability and better load
transient response.
This information along with the ESR graphs, Figures 19, 20, and 29, is included to assist in selection of suitable
capacitance for the user’s application. When necessary to achieve low height requirements along with high
output current and/or high load capacitance, several higher ESR capacitors can be used in parallel to meet
these guidelines.
100
47
10
0.01
OUTPUT CAPACITANCE
vs
EQUIVALENT SERIES RESISTANCE
1000
0.1
ESR − Equivalent Series Resistance − Ω
Output Capacitance − Fµ
Figure 29
Y = ESRmin x C
o
Region of Stability
Region of Instability
ESR min x C
o
= Constant
0.2