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KBMF01SC6

EMI FILTER AND LINE TERMINATION FOR PS/2 MOUSE OR KEYBOARD PORTS

STMicroelectronics 

KBMFxxSC6

To have a good approximation of the remaining voltages at both Vinput and Voutput stages, we give the

typical dynamical resistance value Rd. By taking into account these following hypothesis : Rt>Rd, Rg>Rd

and Rload>Rd, it gives these formulas:

Vinput = Rg.VBR + Rd.Vg

Rg

Voutput = RS.VBR + Rd.Vinput

Rt

The results of the calculation done for VPP=8kV, Rg=330Ω (IEC 61000-4-2 standard), Vbr=7V

(typ.) and Rd = 1ohm (typ.) give:

Vinput = 31.2 V

Voutput = 7.8 V

This confirms the very low remaining voltage across the device to be protected. It is also important to note

that in this approximation the parasitic inductance effect was not taken into account. This could be few

tenths of volts during few ns at the input side. This parasitic effect is not present at the output side due the

low current involved after the resistance RS.

The measurements done here after show very clearly (Fig. A5) the high efficiency of the ESD protection :

- no influence of the parasitic inductances on output stage

- Voutput clamping voltage very close to Vbr (positive strike) and -Vf (negative strike)

Fig. A4: Measurement conditions

ESD

SURGE

16kV

Air

Discharge

TEST BOARD

Vin

Vout

4/8

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