Data Sheet
November 1999
L7581 Ringing Access Switch
Application
VBAT
(REFERENCE)
SW3
SW1
R1
TIP
TIP
SCR
AND
TRIP
CKT
BATTERY
FEED
CROWBAR
PROTECTION
RING
R2
SW2
RING
SW4
RING
GENERATOR
BATTERY
12-3074.e (F)
Figure 7. Typical RAS Application, A Version, Idle, or Talk State Shown
Table 12. Truth Table
INPUT
0 V
TSD
Tip Break Switch Ring Break Switch Ringing Return Switch Ring Switch
5 V/Float1
5 V/Float1
0 V2
On
Off
Off
On
Off
Off
Off
On
Off
Off3
On4
Off5
5 V
Don’t Care
1. Thermal shutdown mechanism is active with TSD floating or equal to 5 V.
2. Forcing TSD to ground overrides the logic input pins and forces an all OFF state.
3. Idle/Talk state.
4. Power ringing state.
5. All OFF state.
A parallel in/parallel out data latch is integrated into the L7581. Operation of the data latch is controlled by the logic
level input pin LATCH. The data input to the latch is the INPUT pin of the L7581, and the output of the data latch is
an internal node used for state control.
When the LATCH control pin is at logic 0, the data latch is transparent and data control signals flow directly from
INPUT, through the data latch to state control. Any changes in INPUT will be reflected in the state of the switches.
When the LATCH control pin is at logic 1, the data latch is active—the L7581 will no longer react to changes at the
INPUT control pin. The state of the switches is now latched; that is, the state of the switches will remain as they
were when the LATCH input transitioned from logic 0 to logic 1. The switches will not respond to changes in INPUT
as long as LATCH is held high.
Note that the TSD input is not tied to the data latch. TSD is not affected by the LATCH input. TSD input will override
state control via INPUT and LATCH.
12
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
