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Document Number: 69998

S-82461-Rev. B, 06-Oct-08

Vishay Siliconix

SiP4613A, SiP4613B

DETAILED DESCRIPTION

The SiP4613A, SiP4613B limits load current by sampling the

pass transistor current and passing that through an external

increase, thereby reducing the gate to source voltage of the

Setting the Current Limit Level

Setting the current limit level on the SiP4613A, SiP4613B

requires some care to ensure the maximum current required

by the load will not trigger the current limit circuitry. The

minimum current limit threshold should be determined by

adding

25 % headroom. The SiP4613A, SiP4613B has a

current limit tolerance of 25 %, which is largely a result of

process variations from part to part, and also temperature

and

current limit is never below the desired current limit a 1/0.80

= 1.25 coefficient needs to be added to the calculations.

Knowing the maximum load current required, the value of

values

given

a

limit

current

refer

to

the

"Typical

Characteristics" section.

Operation at Current Limit and Thermal Shutdown

SiP4613A, SiP4613B the load current will stay fixed at the

required current is not supplied, the voltage at OUT will drop.

more heat. The power dissipation for the SiP4613A,

SiP4613B can be expressed as

Once this exceeds the maximum power dissipation of the

package, the die temperature will rise. When the die

temperature exceeds an over-temperature limit of 165 °C,

the SiP4613A, SiP4613B will shut down until it has cooled

down to 145 °C, before starting up again. As can be seen in

the figure below, the SiP4613A, SiP4613B will continue to

cycle on and off until the load is reduced or the part is turned

off (see figure 4 on next page).

The maximum power dissipation in any application is

dependant

on

the

maximum

junction

temperature,

for the TSC75-6 package,

θ

It then follows that assuming an ambient temperature of

70 °C, the maximum power dissipation will be limited to about

419 mW.

SiP4613. A typical 5 k

Ω resistor is required to connect

current limit status of the device. Figure 2 shows the voltage

Figure 2

output short circuit status. It is also used to indicate the

thermal protection status of the device. Once the thermal

protection is activated in the severe output short circuit

thermal protection cycling. Figure 3 shows the voltage

circuit due to the severe short circuit status of the device’s

output.

Figure 3

The thermal protection is the final protection to the device.

The device will be completely shut down including the open

temperature drop below 145 °C.

131

125

(max)

(max)

A

A

J

A

J

T

T

T

P

-

=

-

=

-

θ

CL (500 mV/div)

50 µs/div

CL (2 V/div)

20 ms/div