TS2012FC datasheet(22/31 Pages) STMICROELECTRONICS

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Application information

TS2012FC

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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 -3 dB 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 and it changes with the

gain setting. There is also a tolerance around the typical values (see Table 5 to Table 7).

Figure 36.

Cut-off frequency vs. input capacitor

4.5

Decoupling of the circuit

Power supply capacitors, referred to as CS1 and CS2 are needed to correctly bypass the

TS2012.

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

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

A 1 µF ceramic capacitor (CS1) between PVCC and PGND and one additional ceramic

capacitor 0.1 µF (CS2) are enough. A 1 µF capacitor must be located as close as possible to

the device PVCC pin in order to avoid any extra parasitic inductance or resistance 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

π Z

⋅⋅

⋅

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

π Z

⋅⋅

⋅

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

0.1

100

G=24dB

Zin=7.5k

Ω typ.

G=18dB

Zin=15k

Ω typ.

G=6dB, G=12dB

Zin=30k

Ω typ.

Tamb=25

°C

Input Capacitor Cin (

μF)

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