Application information

TS2012

22/29

DocID14236 Rev 2

4.4

Low frequency response

If a low frequency bandwidth limitation is required, it is possible to use input coupling

capacitors. In the low frequency region, the input coupling capacitor, Cin, starts to have an

effect. Cin, with the input impedance Zin, forms a first order, high-pass filter with a -3 dB cut-

off frequency (see Table 5 to Table 7) as shown in Equation 1:

Equation 1

So, for a desired cut-off frequency, FCL, Cin is calculated as shown in Equation 2:

Equation 2

with FCL in Hz, Zin in Ω and Cin in F.

The input impedance Zin is typically 30 kΩ for the whole power supply voltage range. There

is also a tolerance around the typical value (see Table 5 to Table 7). The maximum and

minimum tolerance of the FCL can be calculated using Equation 3 and Equation 4

respectively.

Equation 3

Equation 4

4.5

Decoupling of the circuit

Power supply capacitors, referred to as CS, CSL, and CSR are needed to correctly bypass

the TS2012.

The TS2012 has a typical switching frequency of 280 kHz and an output fall and rise time of

about 5 ns. Due to these very fast transients, careful decoupling is mandatory.

A 1 µF ceramic capacitor between each PVCC and PGND and also between AVCC and

AGND is enough, but they must be located very close to the TS2012 in order to avoid any

extra parasitic inductance created by a long track wire. Parasitic loop inductance, in relation

to di/dt, introduces overvoltage that decreases the global efficiency of the device and may

also cause a TS2012 breakdown if the parasitic inductance is too high.

In addition, even if a ceramic capacitor has an adequate high frequency ESR value, its

current capability is also important. A 0603 size is a good compromise, particularly when a

4

Ω load is used.

FCL

1

2

π Zin Cin

⋅⋅

⋅

--------------------------------------------

=

Cin

1

2

π Zin FCL

⋅⋅

⋅

----------------------------------------------

=

FCLmax

1.103

FCL

⋅

=

FCLmin

0.915

FCL

⋅

=