TS2012 datasheet(23/30 Pages) STMICROELECTRONICS

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TS2012

Application information

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

off frequency (see Table 5 to Table 7):

So, for a desired cut-off frequency FCL Cin is calculated as follows:

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

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

is also a tolerance around the typical value (see Table 5 to Table 7). You can also calculate

the tolerance of the FCL:

●

4.5

Decoupling of the circuit

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

TS2012.

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

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

A 1µF 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

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

cause, if this parasitic inductance is too high, a TS2012 breakdown.

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

Ω load is used.

Another important parameter is the rated voltage of the capacitor. A 1µF/6.3V capacitor

used at 5V, loses about 50% of its value. With a power supply voltage of 5V, the decoupling

value, instead of 1µF, could be reduced to 0.5µF. As CS has particular influence on the

THD+N in the medium to high frequency region, this capacitor variation becomes decisive.

In addition, less decoupling means higher overshoots which can be problematic if they reach

the power supply AMR value (6V).

π Z

⋅⋅

⋅

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

π Z

⋅⋅

⋅

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

CLmax

1.103

⋅

CLmin

0.915

⋅

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