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PDF L9705 Data sheet ( Hoja de datos )

Número de pieza L9705
Descripción DOUBLE QUAD CONTACT INTERFACE CIRCUIT
Fabricantes STMicroelectronics 
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L9705
DOUBLE QUAD CONTACT INTERFACE CIRCUIT
ADVANCE DATA
OPERATING DC SUPPLY VOLTAGE RANGE
5V TO 25V
SUPPLY OVERVOLTAGE PULSE UP TO 40V
VERY LOW STAND-BY QUIESCENT CUR-
RENT, MAX 50µA
INTERNAL CLAMPING DIODES AT CONTACT
INPUTS TO Vs AND gnd WITH PULSE CUR-
RENT CAPABILITY UP TO +50mA, -75mA
CHIP ENABLE FUNCTION AND TRISTATE
OUTPUTS FOR PARALLEL BUS CONNECTION
NOMINAL CONTACT CURRENTS OF 10mA
DEFINED WITH EXTERNAL CONTACT SE-
RIES RESISTORS RIN1-8
CONTACT STATUS MONITORING BY
MEANS OF COMPARING THE RESISTANCE
AT CONTACT SENSE INPUTS WITH THE IN-
TERNAL REFERENCE RESISTOR VALUE
RESISTANCE COMPARING WITH HYSTER-
ESIS FOR HIGH NOISE IMMUNITY AND IM-
MUNITY TO GROUND AND BATTERY PO-
TENTIAL DIFFERENCES
DIP 20
SO20L
ORDERING NUMBERS : L9705
DESCRIPTION
The L9705 is a bipolar monolithic integrated cir-
cuit for monitoring the status of up to four con-
tacts connected to GND and up to four contacts
connected to the battery. The contact sense input
supply the contact current and perform the con-
tact resistance comparison function.
At the output the contact status is translated into
a logical LOW level (contact closed) or logical
HIGh level (contact open).
BLOCK DIAGRAM
January 1992
1/8
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.

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L9705 pdf
L9705
The L9705 circuit compares the input current with
the current through the internal reference resistor.
The device is designed to work with an external
input series resistor of RIN1-8 = 1K. With this in-
put resistor the contact current, when the contact
is closed and the device activated (EN =LOW) is:
IIN
=
VS 2V
1K
,for
GND
contacts,
(1)
IIN
=
VBAT
+
VBAT
1K
2V,
for
VBAT
contacts,
(2)
For this calculation the limit value of the VS to VIN
and VIN saturation voltage of 2V was considered
so that the lowest limit value of IIN is calculated in
(1) and (2)
Figure 4: The output voltage as a function of the input resistance at the corresponding sense input.
The function of the circuit can be demonstrated
with the transfer characteristics, showing the out-
put status as a function of the input resistor RI,
shown in figure 4. The input resistor is a sum of
the RIN and the contact resistance RCON or
RCOFF, for the closed contact:
RI = RIN + RCON, (3)
and for the open contact:
RI = RIN + RCOFF, (4)
The output goes HIGH when the input resistance
increases above 5.3K(GND contacts) or 6.5K
(VBAT contacts) and goes LOW, when the input
resistance decreases below 4K(GND contacts)
or 4.8K(VBAT contacts); these values are typical
values for the switching thresholds. The limit val-
ues of RI = 1.8K(GND contacts) and RI =
1.8K(VBAT contacts) for LOW and RI = 20K
(GND contacts) and 29K(VBAT contacts) for
HIGH implies that a contact with RCON = 100( at
IIN = 10mA) will be recognized as ON = LOW and
a contact with RCOFF = 19K(GND contacts) or
28K(VBAT contact) will be recognized as OFF =
HIGH.
These limits are valid within the supply voltage
range 6V < VS < 16V, the ground potential differ-
ence of VGND = 0.1VS, the battery voltage poten-
tial difference of VBAT < 0.1VBAT and the vari-
ation of the reverse battery protection diode D1
voltage from 0.5V to 1V.
The internal clamping diodes at the contact moni-
toring inputs together with the external contacts
series resistors RIN allows to withstand the tran-
sients at the contact connection.The contact se-
ries resistor RIN limits the input current at the tran-
sient.
The dynamic behaviour of the circuit is defined
with the times tdo and tdTS. When the contact is
open, the input capacitor CIN must be charged
through the resistor RIN. In this case the total de-
lay time tdo may be influenced also with the time
constant RINCIN.
The delay time tdTS, when disabling the device, is
defined only with the internal circuitry. In both
cases, output external capacitance less than
50pF is assumed, the internal output capacitance
of the tristate buffers are less than 5pF.
5/8

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