CPC7691BA datasheet(14/16 Pages) IXYS

14 / 16 page

INTEGRATED CIRCUITS DIVISION

www.ixysic.com

R01

CPC7691

of switching power diodes connected to FGND, one

from TBAT and the other from RBAT, oriented to forward

conduct whenever the potential at either TBAT or RBAT

becomes positive with respect to FGND.

For negative potential fault situations, the CPC7691BA

utilizes a voltage fold-back SCR to direct fault currents

to FGND, away from the external devices, while the

CPC7691BB uses a pair of switching power diodes to

direct the fault currents to VBAT.

The SCR protection technique of the CPC7691BA

uses the VBAT supply as a reference and as a current

source for the SCR trigger to activate the SCR. During

a negative transient event resulting in a bias at TBAT or

RBAT of 2V to 4V more negative than VBAT, the SCR

conducts and faults are shunted to FGND. In order for

the SCR to crowbar (or foldback), the SCR’s

on-voltage (see “Protection Circuitry Electrical

Specifications” on page 8) must be less than the applied

voltage at the VBAT pin. If the VBAT voltage is less

negative than the SCR on-voltage, or if the VBAT

supply is unable to source the trigger current, the SCR

will not crowbar.

Unlike the CPC7691BA which uses one-half of a

diode bridge and an SCR for the internal protection,

the CPC7691BB instead uses a full diode bridge to

clamp both polarities of a transient fault. In the

CPC7691BB a pair of power switching diodes are

used to direct excessive negative potentials at the

TBAT and RBAT nodes into VBAT. These diodes are

oriented so that anytime the potentials at the TBAT or

RBAT nodes become more negative than VBAT they

forward conduct.

Because these diodes direct negative potential faults

to the VBAT pin, the battery supply must be capable of

sourcing currents equal in magnitude to the total

currents of all simultaneous faults. As mentioned

earlier, the fault currents are restricted by the current

limits of the break switches.

Use of the CPC7691BA is recommended for

applications where the local VBAT supply is incapable

of sourcing the cumulative transient current demands

of simultaneous multiple port faults.

2.10.3 Thermal Shutdown

The thermal shutdown mechanism activates when the

device die temperature reaches a minimum of 110

C,

placing the device in the All-Off state regardless of

logic input. During thermal shutdown events the TSD

pin will output a logic low with a nominal 0V level. A

logic high is output from the TSD pin during normal

operation with a typical output level equal to VDD.

When presented with short duration transients such

as a lightning event, the thermal shutdown feature will

typically not activate. But in an extended power-cross

event, fault currents limited by the DC current limit

function flowing through the active switches will cause

the device temperature to rise until the thermal

shutdown mechanism activates. Activation of the

thermal shutdown mechanism forces the CPC7691

into the All-Off state. At this point the current

measured into TLINE or RLINE will drop to zero. Once

the device enters thermal shutdown it will remain in

the All-Off state until the device temperature drops

below the de-activation level of the thermal shutdown

circuit. This permits the device to autonomously return

to normal operation.

If the fault condition has not passed, the limited current

will again flow through the active switches and heating

will resume, reactivating the thermal shutdown

mechanism. This cycle of entering and exiting the

thermal shutdown mode will continue as long as the

fault condition persists. If the magnitude of the fault

condition is great enough, the external secondary

protector will activate shunting the fault current to

ground.

2.11 External Protection Elements

The CPC7691 requires only over-voltage secondary

protection on the loop (line) side of the device. The

integrated protection feature described above negates

the need for additional external protection on the SLIC

side. The secondary protector must limit voltage

transients to levels that do not exceed the breakdown

voltage or input-output isolation barrier of the

CPC7691. A foldback or crowbar type protector is

recommended to minimize stresses on the switches.

Consult IXYS Integrated Circuits Division’s application

note, AN-144, Impulse Noise Benefits of Line Card Access

Switches for equations related to the specifications of

external secondary protectors, fuse resistors and

PTCs.

CPC7691BA датащи(PDF) 14 Page - IXYS Corporation

CPC7691BA датащи(HTML) 14 Page - IXYS Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

датащи скачать

ссылки URL