CPC7594 datasheet(17/20 Pages) IXYS

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INTEGRATED CIRCUITS DIVISION

CPC7594

R04

www.ixysic.com

2.8 Battery Voltage Monitor

The CPC7594 also uses the VBAT voltage to monitor

battery voltage. If system battery voltage is lost, the

CPC7594 immediately enters the all-off state. It

remains in this state until the battery voltage is

restored. The device also enters the all-off state if the

battery voltage rises more positive than about –10 V

with respect to ground and remains in the all-off state

until the battery voltage drops below approximately

–15 V with respect to ground. This battery monitor

feature draws a small current from the battery (less

than 1

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

overall power dissipation.

This monitor function performs properly if the

CPC7594 and SLIC share a common battery supply

origin. Otherwise, if battery is lost to the CPC7594 but

not to the SLIC, then the VBAT pin will be internally

biased by the potential applied at the TBAT or RBAT

pins via the internal protection circuitry SCR trigger

current path.

2.9 Protection

2.9.1 Diode Bridge/SCR

The CPC7594 uses a combination of current limited

break switches, a diode bridge/SCR clamping circuit,

and a thermal shutdown mechanism to protect the

SLIC device or other associated circuitry from damage

during line transient events such as lightning. During a

positive transient condition, the fault current is

conducted through the diode bridge to ground via

FGND. Voltage is clamped to a diode drop above

ground. During a negative transient of 2 to 4 V more

negative than the voltage source at VBAT, the SCR

conducts and faults are shunted to FGND via the SCR

or the diode bridge.

In order for the SCR to crowbar (or foldback), the

SCR’s on-voltage (see “Protection Circuitry Electrical

Specifications” on page 10) 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.

For power induction or power-cross fault conditions,

the positive cycle of the transient is clamped to a diode

drop above ground and the fault current directed to

ground. The negative cycle of the transient will cause

the SCR to conduct when the voltage exceeds the

VBAT reference voltage by two to four volts, steering

the fault current to ground.

Note: The CPC7594xB does not contain the

protection SCR but instead uses diodes to clamp both

polarities of a transient fault. These diodes direct the

negative potential’s fault current to the VBAT pin.

2.9.2 Current Limiting function

If a lightning strike transient occurs when the device is

in the talk state, the current is passed along the line to

the integrated protection circuitry and restricted by the

dynamic current limit response of the active switches.

During the talk state, when a 1000V 10x1000

s

lightning pulse (GR-1089-CORE) is applied to the line

though a properly clamped external protector, the

current seen at TLINE and RLINE will be a pulse with a

typical magnitude of 2.5 A and a duration less than

0.5

s.

If a power-cross fault occurs with the device in the talk

state, the current is passed though break switches

SW1 and SW2 on to the integrated protection circuit

but is limited by the dynamic DC current limit response

of the two break switches. The DC current limit

specified over temperature is between 80 mA and

425 mA and the circuitry has a negative temperature

coefficient. As a result, if the device is subjected to

extended heating due to a power cross fault condition,

the measured current at TLINE and RLINE will decrease

as the device temperature increases. If the device

temperature rises sufficiently, the temperature

shutdown mechanism will activate and the device will

enter the all-off state.

2.10 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 0 V level. A

logic high is output from the TSD pin during normal

operation with a typical output level equal to VDD.

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