ISL5586FCM datasheet(13/20 Pages) INTERSIL

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4-13

Power Denial

Overview

The power denial mode (111) will shutdown the entire device

except for the logic interface. Loop supervision is not

provided. This mode may be used as a sleep mode or to

shut down the SLIC in the presence of fault conditions.

Switching between high and low battery will have no effect

during power denial.

Functionality

During power denial, both the Tip and Ring amplifiers are

disabled, presenting high impedances to the line. The

voltages at both outputs are near ground.

Thermal Shutdown

In the event the safe die temperature is exceeded due to a fault

condition the device will automatically shut down. The thermal

shutdown threshold is approximately 170

ºC.When the device

cools to a temperature below the thermal threshold it will power

back up automatically. If the fault persists the part will continue

to go in and out of thermal shutdown which can be observed as

an oscillation on Tip or Ring. Programming power denial will

shut down the device and stop the self cooling cycle.

Battery Switching

Overview

The integrated battery switch selects between high battery

and low battery operation. The battery switch is controlled with

the logic input BSEL. When BSEL is a logic high, the high

battery (VBH) is selected. A logic low will enable the low

battery (VBL). All operating modes of the SLIC will function

from high or low battery, but it is strongly recommended

Forward Loop Back be enabled only with the low battery.

Functionality

The logic control is independent of the operating mode

decode. Independent logic control provides the most

flexibility and will support all application configurations.

When changing device operating states, battery switching

should occur simultaneously with or prior to changing the

operating mode. In most cases, this will minimize overall

power dissipation and prevent glitches on the DET output.

The only external component required to support the battery

switch is a diode in series with the VBH supply lead. In the

event that high battery is removed, the diode allows the

device to transition to low battery operation.

Low Battery Operation

All off hook operating conditions should use the low battery

to minimize power dissipation. A typical low battery

operating voltage for the SLIC is -24V, however this may be

increased to support longer loop lengths or high loop

current requirements. Standby conditions may also operate

from the low battery if MTU compliance is not required,

further reducing standby power dissipation.

High Battery Operation

Other than ringing, the high battery should be used for

standby conditions which must provide MTU compliance.

During standby operation the power consumption is typically

85mW with -100V battery. If ringing requirements do not

require full 100V operation, then a lower battery will result in

lower standby power.

High Voltage Decoupling

The 100V rating of the SLIC dictates a capacitor of higher

voltage rating be used for decoupling. Suggested decoupling

values for all device pins are 0.1

µF. If the protection scheme

shown in Figure 15 is implemented the VBH decoupling

capacitor should be increased to 0.47uF. This is done to

minimize the turn-on time of the battrax device during

negative surge transients. Standard surface mount ceramic

capacitors are rated at 100V. For applications driven by low

cost and small size, the decoupling scheme shown in Figure

10 could be implemented.

It is important to place an external diode between the VBH pin

and the decoupling capacitor. Connecting the decoupling

capacitor directly to the VBH pin will degrade the reliability of the

device. Refer to Figure 15 for the proper arrangement. This

applies to both single and stacked and decoupling schemes.

If VBL and VBH are tied together the battery switch function

is overridden. In this case the external diode is not needed

and the decoupling capacitor may be attached directly to

VBH pin.

VBH

VBL

0.22

ISL5586

FIGURE 10. ALTERNATE DECOUPLING SCHEME

FIGURE 11. IMPEDANCE SYNTHESIS

TIP

RING

-IN

VFB

VZO

1:1

CFB

VSA

VTR

V2W

ISL5586

ISL5586FCM Datasheet(PDF) 13 Page - Intersil Corporation

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