Document
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KBMFxxSC6
EMI FILTER AND LINE TERMINATION FOR PS/2 MOUSE OR KEYBOARD PORTS
A.S.D.™
MAIN APPLICATION EMI Filter and line termination for mouse and keyboard ports on: - Desktop computers - Notebooks - Workstations - Servers DESCRIPTION On the implementation of computer systems, the radiated and conducted EMI should be kept within the required levels as stated by the FCC regulations. In addition to the requirements of EMC compatibility, the computing devices are required to tolerate ESD events and remain operational without user intervention. The KBMF implements a low pass filter to limit EMI levels and provide ESD protection which exceeds IEC 61000-4-2 level 4 standard. The device also implements the pull up resistors needed to bias the data and clock lines. The package is the SOT23-6L which is ideal for situations where board space is at a premium. FEATURES Integrated low pass filters for Data and Clock lines Integrated ESD protection Integrated pull-up resistors Small package size Breakdown voltage: VBR = 6V min
s s s s s
SOT23-6L
FUNCTIONAL DIAGRAM
+Vcc Rp Rs
Dat In
C C
Dat Out
Gnd
+Vcc Rp Rs
+Vcc
Clk In
C C
Clk Out
BENEFITS
s s
s
EMI / RFI noise suppression ESD protection exceeding IEC61000-4-2 level 4 High flexibility in the design of high density boards
Rs code 01 Tolerance 39Ω ±10%
Rp 4.7kΩ ±10%
C 120pF ±20%
TM: ASD and TRANSIL are trademarks of STMicroelectronics.
February 2002 - Ed : 1D
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COMPLIES WITH THE FOLLOWING ESD STANDARDS: IEC 61000-4-2 (R = 330Ω C = 150pF), level 4 ±15 kV (air discharge) ±8 kV (contact discharge) MIL STD 883C, Method 3015-6 Class 3 C = 100 pF R = 1500 Ω 3 positive strikes and 3 negative strikes (F = 1 Hz)
ABSOLUTE MAXIMUM RATINGS (Tamb = 25°C) Symbol VPP Tj Tstg TL Top Pr Parameter ESD discharge R = 330Ω C = 150pF contact discharge ESD discharge - MIL STD 883 - Method 3015-6 Junction temperature Storage temperature range Lead solder temperature (10 second duration) Operating temperature Range Power rating per resistor Value ±12 ±25 150 - 55 to +150 260 0 to 70 100 Unit kV kV °C °C °C °C mW
ELECTRICAL CHARACTERISTICS (Tamb = 25°C) Symbol IR VBR VF Parameters Diode leakage current Diode breakdown voltage Diode forward voltage drop Test conditions VRM = 5.0V IR = 1mA IF = 50mA 6 0.9 Min Typ Max 10 Unit µA V V
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TECHNICAL INFORMATION EMI FILTERING The KBMFxxSC6 ensure a filtering protection against ElectroMagnetic and RadioFrequency Interferences thanks to its low-pass filter structure. This filter is characterized by the following parameters : - cut-off frequency - Insertion loss - high frequency rejection Fig. A1: Measurements configuration Fig. A2: KBMFxxSC6 attenuation curve
Insertion loss (dB) 0
-10
50 Ω
TEST BOARD
TG OUT
KM1
RF IN
Vg
50 Ω
-20
-30
-40 1 10 F (MHz) 100 1000
ESD PROTECTION The KBMFxxSC6 is particularly optimized to perform ESD protection. ESD protection is based on the use of device which clamps at : Vouput = VBR + Rd .IPP This protection function is splitted in 2 stages. As shown in figure A3, the ESD strikes are clamped by the first stage S1 and then its remaining overvoltage is applied to the second stage through the resistor R. Such a configuration makes the output voltage very low at the Voutput level. Fig. A3: ESD clamping behavior
Rg
S1
Rs Vinput Voutput
S2
Rd
Rd
VPP
Rload
VBR
VBR
Device to be protected
ESD Surge
KBMFxxSC6
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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: Rg .VBR + Rd .Vg Vinput = Rg RS .VBR + Rd .Vinput Voutput = Rt The results of the calculation done for V PP =8kV, Rg=330 Ω (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
KM1
Vin
Vout
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Fig. A5: Remaining voltage at both stages S1 (Vinput) and S2 (Voutput) during ESD surge.
a. Positive surge
b. Negative surge
Please note that the KBMFxxSC6 is not only acting for positive ESD surges but also for negative ones. For these kind of disturbances it clamps close to ground voltage as shown in Fig. A5b. LATCH-UP PHENOMENA The early ageing and destruction of .