Data Sheet

26

Rev. 1.2, 2015-01-15

TLS205B0

Application Information

voltage noise in the considered bandwidth. For a given output voltage actual numbers of the output voltage noise

will - next to the bypass capacitor itself - be dependent on the capacitance of the applied output capacitor

C

its ESR: In case of the TLS205B0EJV / TLS205B0LDV applied with unity gain (i.e.

V

bypass capacitor of 10 nF in combination with a (low ESR) ceramic

C

numbers of typical 41

µV

conditions by adding a small resistor of ~250 mΩ in series to the 10 µF ceramic output capacitor acting as

additional ESR. A reduction of the output voltage noise can also be achieved by increasing capacitance of the

output capacitor. For

C

can again be further lowered to 24

µV

fix voltage version TLS205B0EJV33 / TLS205B0LDV33 the output voltage noise for the described cases vary from

45

µV

10)” on Page 12,, of the

Electrical Characteristics. Please note that next to reducing the output voltage noise level the usage of a bypass

capacitor has the additional benefit of improving transient response which will be also explained in the next

chapter. However one needs to take into consideration that on the other hand the regulator start-up time is

proportional to the size of the bypass capacitor and slows down to values around 15 ms when using a 10 nF

bypass capacitor in combination with a 10 µF

C

6.4

Output Capacitance and Transient Response

The TLS205B0 is designed to be stable with a wide range of output capacitors. The ESR of the output capacitor

is an essential parameter with regard to stability, most notably with small capacitors. A minimum output capacitor

of 3.3 µF with an ESR of 3 Ω or less is recommended to prevent oscillations. Like in general for LDO’s the output

transient response of the TLS205B0 will be a function of the output capacitance. Larger values of output

capacitance decrease peak deviations and thus improve transient response for larger load current changes.

Bypass capacitors, used to decouple individual components powered by the TLS205B0 will increase the effective

output capacitor value. Please note that with the usage of bypass capacitors for low noise operation either larger

values of output capacitors may be needed or a minimum ESR requirement of

C

also typical performance graph “ESR(CQ) with CBYP = 10 nF versus Output Capacitance CQ” on Page 21 as

example). In conjunction with the usage of a 10 nF bypass capacitor an output capacitor

C

6.8 µF is

recommended. The benefit of a bypass capacitor to the transient response performance is impressive and

illustrated as one example in Figure 8 where the transient response of the TLS205B0EJV33 to one and the same

load step from 100 mA to 500 mA is shown with and without a 10 nF bypass capacitor: for the given configuration

of

C

C

to the shorter reaction time of the regulator by adding the bypass capacitor not only the settling time improves but

also output voltage deviations due to load steps are sharply reduced.

Figure 8

Influence of

C

without

C

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0

100

200

300

400

500

600

700

800

900

1000

Time (μs)

C_BYP = 0nF

C_BYP = 10nF