ISL5571A Datasheet, PDF (7/12 Pages) Intersil Corporation – Access High Voltage Switch

ISL5571A
TABLE 9. TRUTH TABLE - ISL5571A
LOGIC INPUTS
SWITCH CONDITION
LOGIC STATE
IDLE / TALK
LATCH INPUT
0
0
T_SD
1 or Floating (Note 11)
TIP LINE BREAK RING LINE BREAK
SWITCH
SWITCH
ON
ON
RINGING
RETURN RING ACCESS
SWITCH
SWITCH
OFF
OFF
POWER RINGING
0
1
1 or Floating (Note 11)
OFF
OFF
ON
ON
IDLE / TALK
1
0
1 or Floating (Note 11)
ON
LATCHED (Note 12)
ON
OFF
OFF
POWER RINGING
1
LATCHED (Note 12)
1
1 or Floating (Note 11)
OFF
OFF
ON
ON
All OFF
X
X
0 (Note 13)
OFF
OFF
OFF
OFF
NOTES:
11. Thermal shutdown mechanism is active with TSD floating or equal to 5V.
12. If the LATCH pin is low, the logic state of the device is controlled by the INPUT pin. When the LATCH pin goes high, the current logic state is
latched. As long as the LATCH pin is held high, the device will no longer respond to any changes applied to the INPUT control pin. The state of
the device will be permanently latched until the LATCH pin is taken low.
13. Setting TSD to a logic low overrides the LATCH and INPUT logic pins and forces all switches to turn OFF.
Circuit Operation and Design Information
Introduction
The ISL5571A was designed to be used in subscriber line
card applications. A typical application circuit is shown in
Figure 1. Its main purpose is to momentarily disconnect the
voice circuit (SLIC and CODEC) and connect an external
ring generator to ring the phone. This function has been
traditionally done by electromechanical relays. The
ISL5571A offers the system designer a solid-state switching
solution with distinct advantages over the electromechanical
relay. These advantages are as follows:
• Lower power consumption (20mW vs. 150mW for the
relay)
• Smaller size, surface mounted package
• Bounce-Free switching
• Lower impulse noise, Low EMI
• Longer life
• Provides current limiting, thermal shutdown, and over-
voltage protection for the SLIC and CODEC
Their bounce-free operation, long lifetime, small size, and
low power consumption make the solid-state access switch
the preferred choice over electromechanical relays
whenever board area, high reliability, and heat reduction are
primary concerns.
The ISL5571A was designed to be a drop in replacement for
the Lucent ATTL7581AAE LCAS device. The Intersil
ISL5571A offers superior r_ON matching between the line
break switches for optimal longitudinal balance, higher
temperature operation (enabling continuous operation in
short loop, high Ringer Equivalency Number applications)
and with 3V TTL logic controlled inputs.
Basic Functional Description
This section describes the basic operation of the ISL5571A.
From the application circuit shown in Figure 1, the ISL5571A
consists of four switches, the Line Break switches (SW1,
SW2), the Ring Return switch (SW3), and the Ring Access
switch (SW4). The Line Break switches (SW1 and SW2)
open and close in unison to connect and disconnect the
voice / data signal from the phone. The Ring Access switch
and the Ring Return switch (SW3 and SW4) open and close
in unison, to connect and disconnect the external ring
generator to the phone.
The ISL5571A has three possible operating states: the Idle /
Talk state, the Power Ringing state, and the All OFF state. It
also has a built in Logic State Latch. The Logic State Latch
enables the user to latch the logic state of the ISL5571A in
either the Idle / Talk state or the Power Ringing state.
The three control logic pins for the ISL5571A are the INPUT
pin, the TSD pin and the LATCH pin. These logic pins are
controlled by TTL logic levels (0V - 0.8V for logic low and
2.4V - 5.0V for logic high). The combination of the logic
levels applied at these pins determine which of the three
logic states the device will be in and whether the Logic State
Latch is active. The truth table for the ISL5571A is shown in
Table 9. A description of each operating state and the
control logic pins follows:
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