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TPS84A20

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SLVSBC6C – MARCH 2013 – REVISED DECEMBER 2019

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10.2 Capacitor Recommendations for the TPS84A20 Power Supply

10.2.1 Capacitor Technologies

10.2.1.1 Electrolytic, Polymer-Electrolytic Capacitors

When using electrolytic capacitors, high-quality, computer-grade electrolytic capacitors are recommended.

Polymer-electrolytic type capacitors are recommended for applications where the ambient operating temperature

is less than 0°C. The Sanyo OS-CON capacitor series is suggested due to the lower ESR, higher rated surge,

power dissipation, ripple current capability, and small package size. Aluminum electrolytic capacitors provide

adequate decoupling over the frequency range of 2 kHz to 150 kHz, and are suitable when ambient temperatures

are above 0°C.

10.2.1.2 Ceramic Capacitors

The performance of aluminum electrolytic capacitors is less effective than ceramic capacitors above 150 kHz.

Multilayer ceramic capacitors have a low ESR and a resonant frequency higher than the bandwidth of the

regulator. They can be used to reduce the reflected ripple current at the input as well as improve the transient

response of the output.

10.2.1.3 Tantalum, Polymer-Tantalum Capacitors

Polymer-tantalum type capacitors are recommended for applications where the ambient operating temperature is

less than 0°C. The Sanyo POSCAP series and Kemet T530 capacitor series are recommended rather than many

other tantalum types due to their lower ESR, higher rated surge, power dissipation, ripple current capability, and

small package size. Tantalum capacitors that have no stated ESR or surge current rating are not recommended

for power applications.

10.2.2 Input Capacitor

The TPS84A20 requires a minimum input capacitance of 44 μF of ceramic type. An additional 100 µF of non-

ceramic capacitance is recommended for applications with transient load requirements. The voltage rating of

input capacitors must be greater than the maximum input voltage. At worst case, when operating at 50% duty

cycle and maximum load, the combined ripple current rating of the input capacitors must be at least 5 Arms.

Table 6 includes a preferred list of capacitors by vendor. It is also recommended to place a 0.1-µF ceramic

capacitor directly across the PVIN and PGND pins of the device. When operating with split VIN and PVIN rails,

place 4.7 µF of ceramic capacitance directly at the VIN pin.

10.2.3 Output Capacitor

The required output capacitance is determined by the output voltage of the TPS84A20. See Table 5 for the

amount of required capacitance. The effects of temperature and capacitor voltage rating must be considered

when selecting capacitors to meet the minimum required capacitance. The required output capacitance can be

comprised of all ceramic capacitors, or a combination of ceramic and bulk capacitors. The required capacitance

must include at least one 47 µF ceramic. When adding additional non-ceramic bulk capacitors, low-ESR devices

like the ones recommended in Table 6 are required. The required capacitance above the minimum is determined

by actual transient deviation requirements. See Table 7 for typical transient response values for several output

voltage, input voltage and capacitance combinations. Table 6 includes a preferred list of capacitors by vendor.

(1)

Minimum required must include at least one 47-µF ceramic capacitor.

Table 5. Required Output Capacitance

VOUT RANGE (V)

MINIMUM REQUIRED COUT (µF)

MIN

MAX

0.6

< 0.8

500 µF (1)

0.8

< 1.2

300 µF (1)

1.2

< 3.0

200 µF (1)

3.0

< 4.0

100 µF (1)

4.0

5.5

47 µF ceramic