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L9705-L9705D
DOUBLE QUAD CONTACT INTERFACE CIRCUIT
L9705DOUBLE QUAD CONTACT INTERFACE CIRCUIT
ADVANCE DATAOPERATING 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
DESCRIPTIONThe 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
ABSOLUTE MAXIMUM RATINGS
PIN CONNECTION (top view)
THERMAL DATA
L9705
ELECTRICAL CHARACTERISTICS (VS = 5 to 25V, VCC = 4.75 to 5.25V, Vbat -0.5V < VS ,< Vbat -1V , Tj = –40 to 150°C unless otherwise specified.)
NOTES:
1) The input resistor threshold value is a resistor value from the IN-pin to ground at which the corresponding output changes its status (fig.4)
2) ΣIIN is the sum of the IN5 to IN8 input currents.
3) The delay times are defined from the crossing point of 50% initiating signal amplitude to the crossing point of 50% output signal amplitude
L9705
FUNCTIONAL DESCRIPTIONThe L9705 circuit monitors the status of the con-
tacts which are connected through the series ex-
ternal resistors RIN to the contact sense input
pins. The contacts equivalent circuit is supposed
to be as shown in fig.2 for GND connected con-
tacts (IN 1 to 4) and as shown in fig. 3 for VBAT
connected contacts (IN 5 to 8).
Figure 1: Typical application diagram for the L9705 circuit. The current flowing in the arrow direction isassumed positive. The external capacitors CIN and COUT represent the total wiring
capacitance at the corresponding pins.
Figure 2: The contact sense input connection with the contact equivalent circuit for GND connectedcontacts.
Figure 3: The contact sense input connection with the contact equivalent circuit for VBAT connectedcontacts.
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 = 1KΩ. With this in-
put resistor the contact current, when the contact
is closed and the device activated (EN =LOW) is:
IIN = VS − 2V
1KΩ ,for GND contacts, (1)
IIN = VBAT + ΔVBAT − 2V
1KΩ , 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 5.3KΩ (GND contacts) or 6.5KΩ
(VBAT contacts) and goes LOW, when the input
resistance decreases below 4KΩ (GND contacts)
or 4.8KΩ (VBAT contacts); these values are typical
values for the switching thresholds. The limit val-
ues of RI = 1.8KΩ (GND contacts) and RI =
1.8KΩ (VBAT contacts) for LOW and RI = 20KΩ
(GND contacts) and 29KΩ (VBAT contacts) for
HIGH implies that a contact with RCON = 100Ω ( at
IIN = 10mA) will be recognized as ON = LOW and
a contact with RCOFF = 19KΩ (GND contacts) or
28KΩ (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 ΔVGND = 0.1VS, the battery voltage poten-
tial difference of ΔVBAT
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.
L9705
