HV320

4

Functional Block Diagram

+

UV

Vee

-

Gate

100mV

+

Vin

buffer

Vbg

+

UVLO

-

-

Regulator

& POR

Logic

Sense

OV

Functional Description

HV320 as a fuse and circuit breaker replacement:

Telecom, data networks, automotive, industrial controls

and some computer applications require the ability to

isolate the power source from a load fault without having

to

physically

replace

a

fuse

or

manually

reset

a

mechanical circuit breaker. Traditionally a fast acting fuse

or Positive Temperature Coefficient (PTC) device such as

Raychem’s PolySwitch or a manual / thermal circuit

breaker have been used to limit the fault current.

The problems with PTCs are numerous. First, they are

extremely temperature dependent. For

example the

required trip current can vary as high as 150% of nominal

value at lower temperatures such as –40

°C and as low as

50% of nominal value at higher temperatures such as

+85

°C.

Second, the ratio of trip current to steady state current can

range from 7 to 70. This implies for an application where

steady state current is 4A, traces must be over designed

to withstand the trip current of 100A, a ratio of 25:1. Third,

PTC’s once tripped, require 20 seconds to minutes to

reset and even when they are reset, the resistance value

can permanently change as much as 240%. This implies

PTC’s

are

not

suitable

for

repeated

short

circuit

applications. Lastly the surface mount PTCs typically have

large end cap terminations that absorb heat during the

reflow process and can result in insufficient solder and

cold solder joints. It is not uncommon for PCB surface

contaminations to be present, thus resulting in poor

solderability, hence loss of yield.

Typically, fuses are rated in Amp^2-seconds. For a SMT

1206 size fast-acting 2A, 63V fuse rated at 0.23 A - square

second, it could take more than 200A for 5

µs before the

fusing element melts.

HV320 is an ideal alternative to thermal and manual circuit

breakers in DC input applications. It has wide variety of

uses in the automotive industry, such as PCB trace /

device protection and DC motors and solenoid actuator

current limit protection. These devices are typically used in

windows and seat adjustment operations as well as

automatic trunk opening mechanisms. Since these

devices are operated manually, they can remain energized

by the operator even after the mechanical lever has

reached its end of travel. In this case, back EMF that

normally opposes the supply voltage will drop to zero and

a large current surge can begin to flow. HV320 can

accurately be programmed to trip the current. In industrial

applications, HV320 can offer broad solutions in DC

solenoid-operated

valves,

DC

motors

and

other

electromagnetic loads.

Fault current magnitude can be scaled to different current

ratings by proper selection of the sense resistor and the

external

N-Channel

MOSFET.

For

higher

current

applications, IGBT devices may be considered. The

HV320 is intended to provide this circuit breaker function

on supply rails in the range of

−10 to −90 Volts.

Description of Operation

During initial application of power, a unique proprietary

circuit holds off the external MOSFET, preventing an input

glitch while an internal regulator establishes an internal

operating voltage of approximately 10V. Until the proper

internal voltage is achieved, all circuits are held reset and

the gate to source voltage of the external MOSFET is

clamped low. Once the internal under voltage lock out