Datasheet

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Output Capacitor
ESR and Transient Response
C
R
ESR
L
ESL
+
V
IN
R
ESR
LDO
I
OUT
V
ESR
C
OUT
R
LOAD
V
OUT
TPS752xxQ
TPS754xxQ
SLVS242C MARCH 2000 REVISED OCTOBER 2007
As with most LDO regulators, the TPS752xxQ and TPS754xxQ require an output capacitor connected between
OUT and GND to stabilize the internal control loop. The minimum recommended capacitance value is 47 μ F and
the ESR (equivalent series resistance) must be between 100 m and 10 . Solid tantalum electrolytic, aluminum
electrolytic, and multilayer ceramic 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 (see Figure 20 and Figure 21 ), 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.
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 22 .
Figure 22. 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..
Figure 23 shows the output capacitor and its parasitic impedances in a typical LDO output stage.
Figure 23. LDO Output Stage With Parasitic Resistances ESR and ESL
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