Datasheet

R
ESR
L
ESL
C
TPS70245, TPS70248
TPS70251, TPS70258
TPS70202
www.ti.com SLVS286E –JUNE 2000–REVISED DECEMBER 2009
APPLICATION INFORMATION
Input Capacitor
For a typical application, an input bypass capacitor (0.1μF to 1μF) is recommended. This capacitor filters any
high-frequency noise generated in the line. For fast transient conditions where droop at the input of the LDO may
occur because of high inrush current, it is recommended to place a larger capacitor at the input as well. The size
of this capacitor depends on the output current and response time of the main power supply, as well as the
distance to the V
I
pins of the LDO.
Output Capacitor
As with most LDO regulators, the TPS702xx requires an output capacitor connected between OUT and GND to
stabilize the internal control loop. The minimum recommended capacitance values are 10μF ceramic capacitors
with an ESR (equivalent series resistance) between 50mΩ and 2.5Ω or 6.8μF tantalum capacitors with ESR
between 250mΩ and 4Ω. Solid tantalum electrolytic, aluminum electrolytic, and multilayer ceramic capacitors with
capacitance values greater than 10μF are all suitable, provided they meet the requirements described above.
Larger capacitors provide a wider range of stability and better load transient response. Table 1 gives a partial
listing of surface-mount capacitors suitable for use with the TPS702xx for fast transient response applications.
This information, along with the ESR graphs, is included to assist in selection of suitable capacitance for user
applications. 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 the guidelines above.
Table 1. Partial Listing of TPS702xx-Compatible Surface-Mount Capacitors
VALUE MANUFACTURER MAXIMUM ESR MFR PART NO.
22μF Kemet 345mΩ 7495C226K0010AS
33μF Sanyo 100mΩ 10TPA33M
47μF Sanyo 100mΩ 6TPA47M
68μF Sanyo 45mΩ 10TPC68M
ESR and Transient Response
LDOs typically require an external output capacitor for stability. In fast transient response applications, capacitors
are used to support the load current while the LDO amplifier is responding. In most applications, one capacitor is
used to support both functions.
Besides its capacitance, every capacitor also contains parasitic impedances. These parasitic impedances are
resistive as well as inductive. The resistive impedance is called equivalent series resistance (ESR), and the
inductive impedance is called equivalent series inductance (ESL). The equivalent schematic diagram of any
capacitor can therefore be drawn as shown in Figure 37.
Figure 37. ESR and ESL
In most cases one can neglect the effect of inductive impedance ESL. Therefore, the following application
focuses mainly on the parasitic resistance ESR.
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