EMI Filter and line termination for mouse and keyboard ports on:
■ Desktop computers
■ Notebooks
■ Workstations
■ Servers
FOR PS/2 MOUSE OR KEYBOARD PORTS
KBMF
FEATURES
■ Integrated low pass filters for Data and Clock
lines
■ Integrated ESD protection
■ Integrated pull-up resistors
■ Small package size
■ Breakdown voltage: V
= 6V min.
BR
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.
ESD discharge R = 330W C = 150pF contact discharge
ESD discharge - MIL STD 883 - Method 3015-6
Junction temperature150°C
Storage temperature range- 55 to +150°C
Lead solder temperature (10 second duration)260°C
Operating temperature Range0 to 70°C
Power rating per resistor100mW
Table 3: Electrical Characteristics (T
amb
= 25°C)
±12
±25
kV
SymbolParametersTest conditionsMinTypMaxUnit
I
R
V
BR
V
F
Diode leakage current
Diode breakdown voltage
Diode forward voltage drop
= 5.0V
V
RM
= 1mA
I
R
= 50mA
I
F
10µA
6V
0.9V
TECHNICAL INFORMATION
1. 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 :
The KBMFxxSC6 is particularly optimized to perform ESD protection. ESD protection is based on the use
of device which clamps at:
V
= VBR + Rd.I
output
This protection function is splitted in 2 stages. As shown in figure 4, 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 V
Figure 4: ESD clamping behavior
PP
output
level.
Rg
V
PP
ESD Surge
To have a good approximation of the remaining voltages at both V
V
Rd
BR
S1
Rs
Vinput
Voutput
KBMFxxSC6
S2
Rd
V
input
BR
and V
Rload
Device
to be
protected
stages, we give the
output
typical dynamical resistance value Rd. By taking into account these following hypothesis : R
and R
=8kV, Rg=330Ω (IEC 61000-4-2 standard), VBR=7V (typ.) and
PP
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 R
.
S
The measurements done here after show very clearly (figure 6) the high efficiency of the ESD protection :
- no influence of the parasitic inductances on output stage
- V
clamping voltage very close to VBR (positive strike) and -VF (negative strike)
output
3/8
KBMF
Figure 5: Measurement conditions
ESD
SURGE
16kV
Air
Discharge
TEST BOARD
KM1
Vin
Vout
Figure 6: Remaining voltage at both stages S1 (V
) and S2 (V
input
) during ESD surge
output
Positive surgeNegative surge
Please note that the KBMF01SC6 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 the Negative Surge figure.
3. LATCH-UP PHENOMENA
The early ageing and destruction of IC’s is often due to latch-up phenomena which is mainly induced by
dV/dt. Thanks to its structure, the KBMF01SC6 provides a high immunity to latch-up phenomena by
smoothing very fast edges.
4/8
4. CROSSTALK BEHAVIOR
Figure 7: Crosstalk phenomena
R
G1
V
G1
R
G2
V
G2
Line 1
Line 2
KBMF
R
L1
R
L2
αβ
αβ
V+ V
1G112G2
V+ V
2G221G1
DRIVERS
RECEIVERS
The crosstalk phenomena is due to the coupling between 2 lines. The coupling factor ( β12 or β21 )
increases when the gap across lines decreases, this is the reason why we provide crosstalk
measurements for monolithic device to guarantee negligeable crosstalk between the lines. In the example
above the expected signal on load R
β
. This part of the VG1 signal represents the effect of the crosstalk phenomenon of the line 1 on the
21VG1
is α2VG2, in fact the real voltage at this point has got an extra value
L2
line 2. This phenomenon has to be taken into account when the drivers impose fast digital data or high
frequency analog signals in the disturbing line. The perturbed line will be more affected if it works with low
voltage signal or high load impedance (few kΩ).
Figure 8: Analog Crosstalk measurements
configuration
TG OUT
50 Ω
Vg
TEST BOARD
KM1
RF IN
50 Ω
Figure9:Typical Analog Crosstalk measurement
crosstalk (dB)
0
-20
-40
-60
-80
-100
-120
1101001,000
F (MHz)
Figure 8 gives the measurement circuit for the analog crosstalk application. In figure 9, the curve shows
the effect of the Data line on the CLK line. In usual frequency range of analog signals (up to 100MHz) the
effect on disturbed line is less than -37dB.
5/8
KBMF
Figure 10: Digital crosstalk measurements
Figure11:Digital crosstalk measurements
configuration
+5V+5V
Square
Pulse
Generator
5KHz
+5V
74HC04
Line 1
V
G1
Line 2
KBMF
01SC6
74HC04
b
V
21
G1
Figure 10 shows the measurement circuit used to quantify the crosstalk effect in a classical digital application.
Figure 11 shows that in such a condition signal from 0 to 5V and rise time of few ns, the impact on the
other line is less than 50mV peak to peak (below the logic high threshold voltage). The measurements
performed with falling edges gives the results within the same range.
5. APPLICATION EXAMPLE
Figure 12: Implementation of KBMFxxSC6 in a typical application
KDAT
KCLK
KBMF
01SC6
Vcc
PS/2 Connector
PS/2 Keyboard
Super I/O
MDAT
KBMF
MCLK
01SC6
PS/2 Mouse
The KBMF01SC6 device could be used on PS/2 mouse or keyboard as indicated by figure 12.
28-Oct-20042SOT23-6L package dimensions change for reference “D”
from 3.0 millimeters (0.118 inches) to 3.05 millimeters
(0.120 inches).
7/8
KBMF
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