le75181 Zarlink Semiconductor, le75181 Datasheet - Page 8

• Manufacturer Part Number: le75181
• Description: Ringing Access Switch
• Manufacturer: Zarlink Semiconductor

ZERO CROSS CURRENT TURN OFF
The ring access switch (SW4) is designed to turn off on the next zero current crossing after application of the appropriate logic
input control. This switch requires a current zero cross to turn off. Switch 4, once on, will remain in the ON state (regardless of
logic input) until a current zero cross. Therefore, to ensure proper operation of switch 4, this switch should be connected, via
proper impedance, to the ringing generator or some other ac source. Do not attempt to switch pure DC with switch 4.
For a detailed explanation of the operation of switch 4, please refer to the An Introduction to Le758X Series of Line Card Access
Switches application note.
SWITCHING BEHAVIOR
When switching from the Power Ringing state to the Idle/Talk state via simple logic level input control, the Le75181 is able to
provide control with respect to the timing when the ringing access contacts are released relative to the state of the line break
contacts.
Make-before-break operation occurs when the line break switch contacts are closed (or made) before the ringing access switch
contact is opened (or broken). Break-before-make operation occurs when the ringing access contact is opened (broke) before
the line break switch contacts are closed (made).
Using the logic level input pins INPUT and TSD, either make-before-break or break-before-make operation of the Le75181 is
easily achieved. The logic sequences for either mode of operation are given in
on page 14
When using an Le75181 device in the make-before-break mode, during the ring-to-idle transition, for a period of up to one-half
the ringing frequency, the ring break switch and the pnpn-type ring access switch can both be in the ON state. This is the
maximum time after the logic signal at IN
so it can close. During this interval, current that is limited to the dc break switch current-limit value will be sourced from the ring
node of the SLIC device.
This current is presented to the internal protection circuit. If the SCR-type protector is used (A/C codes), if by random probability
the ring-to-idle transition occurs during a portion of the ring cycle when the ringing voltage exceeds the protection circuit SCR
turn-on voltage, and if current in excess of the SCR’s turn-on current is also available, the SCR may turn on. Once the SCR is
triggered on, if the SLIC device is capable of supplying current in excess of the holding current, the SCR may be latched on by
the SLIC device.
The probability of this event depends on the characteristics of the given SLIC device and of the holding current of the Le75181A/
C devices. The SCR hold current distribution is designed to be safely away from the test limit of 80 mA for Le75181A device. The
limit for Le75181C device is 110 mA. The higher the distribution, the lower the probability of the latch.
If this situation is of concern for a given board design, either use the A/C series device in the break-before-make mode (eliminates
the original 25 ms current pulse) or use a B series device (eliminates the SCR).
Table 4. Additional Electrical Characteristics
Input Low Voltage
Input High Voltage
Input Leakage Current (high)
Input Leakage Current (low)
Input Leakage Current (high)
INPUT, LATCH
Input Leakage Current (low)
INPUT, LATCH
Input Current (Sourcing from LCAS) (low)
TSD
Temperature Shutdown Requirements*
Shutdown Activation Temperature
Shutdown Circuit Hysteresis
*Temperature shutdown flag (TSD) will be high during normal operation and low during temperature shutdown state.
for an explanation of the logic states.
Digital Input Characteristics
Parameter
RING
has transitioned that the ring access switch is waiting for the next zero current cross
—
—
V
V
V
V
V
—
—
Vlogicin = 5 V
Vlogicin = 0 V
Vlogicin = 5 V
Vlogicin = 0 V
V
DD
DD
DD
DD
DD
Zarlink Semiconductor Inc.
TSD
= 5.5 V, V
= 5.5 V, V
= 5.5 V, V
= 5.5 V, V
= 5.5 V, V
= 0 V
Test Condition
8
BAT
BAT
BAT
BAT
BAT
= –75 V,
= –75 V,
= –58 V,
= –58 V,
= –58 V,
Table 5
Measure
llogicin
llogicin
llogicin
llogicin
I
TSD
—
—
—
—
and
Table
Min
110
2.2
0.5
10
—
—
—
—
—
6. See
Typ
100
125
0.5
1.0
—
—
—
—
—
Table 8,
Max
500
500
150
0.8
2.0
25
—
—
—
Truth
Unit
mA
µA
µA
µA
µA
°C
°C
V
V
Table,