CPC7691BATR datasheet(11/16 Pages) IXYS

11 / 16 page

INTEGRATED CIRCUITS DIVISION

CPC7691

R01

www.ixysic.com

Under all start-up situations the CPC7691 will

condition the internal switch control logic for the All-Off

state thereby ensuring all of the switches will remain

off during power-up. When VDD requirements have

been satisfied the LCAS will complete it’s start-up

procedure in one of three conditions.

For start-up scenario 1, the CPC7691 will transition

from the All-Off state to the state defined by the

INRINGING input when VDD is valid.

For start-up scenarios 2, 3, 5, and 6, the CPC7691 will

power up in the All-Off state and remain there until the

LATCH pin is pulled low. This allows for an indefinite

All-Off state for boards inserted into a powered system

but are not configured for service or boards that need

to wait for other devices to be configured first.

Scenario 4 will start up with all switches in the All-Off

state, but upon the acceptance of a valid VDD the

LCAS will revert to either the Talk state or the Ringing

state, and thereafter may randomly change states

based on input pin leakage currents and loading. This

start-up condition should never be utilized as the

LCAS state after power-up can not be predicted.

For the start-up scenario when TSD = 0 the CPC7691

will condition the internal control logic for the All-Off

state as it does when TSD  0. Start-up behavior with

an initial TSD = 0 is dependent on when TSD is

released with respect to the status of the Under

Voltage Lock Out circuitry. Releasing TSD (which

allows the internal pull-up to raise the input from a

logic level low to a logic level high before, or

concurrent with, the Under Voltage Lock Out

deactivation) has no effect on the start-up behavior,

and the start-up scenarios previously described are

applicable.

With TSD held low beyond the deactivation of the

internal Under Voltage Lock Out control, the device will

remain in the All-Off state regardless of the levels on

the INRINGING or LATCH inputs. However, it is

important to note that the LATCH is fully functional

once the Under Voltage Lock Out deactivates. This

allows the LATCH to be preconfigured to the state

desired with the release of TSD.

2.6 VBAT Pin

Although battery power is not used for switch control, it

is required to direct negative potential faults away from

the SLIC. Because the CPC7691 requires VBAT to

protect the SLIC from negative potential faults, the

CPC7691 will deactivate and enter the All-Off state

whenever VBAT is unavailable.

2.6.1 Protection

In the presence of a negative potential fault the

CPC7691BA will draw current from VBAT to supply

trigger current for the internal integrated protection

circuitry SCR. This integrated SCR is designed to

activate whenever the voltage at TBAT or RBAT drops

2V to 4V below the applied voltage on the VBAT pin.

Because the battery supply at this pin is required to

source trigger current during negative over-voltage

fault conditions at tip and ring, it is important that the

net supplying this current be a low impedance path for

high speed transients such as lightning. This will

permit trigger currents to flow enabling the SCR to

activate, and thereby prevent a fault induced negative

over-voltage event at the TBAT or RBAT nodes.

Although the CPC7691BB does not have the SCR for

negative potential fault protection, it utilizes a power

switching diode from each of the TBAT and RBAT nodes

to VBAT, which forward conduct in the presence of

potentials at these nodes more negative than VBAT.

Proper protection requires VBAT to supply sufficient

current to counter the transient fault currents restricted

by the current limit functions of the break switches.

2.6.2 Battery Voltage Monitor

The CPC7691 also uses the VBAT pin to monitor the

battery voltage. If system battery voltage is lost, the

CPC7691 immediately enters the All-Off state, and

remains in this state until the battery voltage is

restored. An internal detector monitoring the system

battery voltage forces the All-Off state anytime the

battery voltage goes more positive than –10V. The

All-Off state is maintained until the battery voltage

goes more negative than –15 V. This battery monitor

feature draws a small current from VBAT (typically

A) and will add slightly to the device’s overall

power dissipation.

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