HV311LG datasheet(8/21 Pages) SUTEX

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HV301/HV311

Start up Overload Protection

Start up must be achieved within a nominal 100ms as indicated

by the PWRGD pin transition to the active state or the circuit will

reset and an automatic restart will initiate. If there is an output

overload or short circuit during start up, the circuit will be in

current limit for the 100ms time limit (in servo mode). In feedback

capacitor mode the circuit breaker will shutdown the pass FET

before 100ms.

Circuit Breaker

The circuit breaker will trip in less than 5µs when the voltage on

the SENSE pin reaches a nominal 100mV. A resistor in series

with the SENSE pin and a capacitor connected between the

SENSE and V

EE pins may be added to delay the rate of voltage

rise on the SENSE pin, thus permitting a current overshoot and

delaying Circuit Breaker activation.

Automatic Restart

The automatic restart delay time is directly proportional to the

capacitance at the RAMP pin. Automatic restart sequence is

activated whenever the 100ms timeout is reached during start up

or the circuit breaker is tripped.

These equations assume that the load is purely capacitive and

the following definitions apply.

RAMP is the external capacitor connected to the RAMP pin.

RAMP is the output current from the RAMP pin, nominally

10µA, when the voltage drop on R

SENSE resistor is zero.

INT is the internally regulated supply voltage and can range

from 8.5V to 12V.

GS(th) is the gate threshold voltage of the external pass

transistor and may be obtained from its datasheet.

GS(limit) is the external pass transistor gate-source voltage

required to obtain the limit current. It is dependent on the

pass transistor’s characteristics and may be obtained from

the transfer characteristics on the transistor datasheet.

fs is the transconductance of the external pass transistor

and may be obtained from its datasheet.

FB is the internal feedback resistor and is nominally 5kΩ.

LIMIT is the load current when the voltage drop on the RSENSE

resistor is 50mV.

These equations may be used to calculate the minimum value of

RAMP for the most critical system performance characteristics.

For maximum contact bounce duration protection choose a

value for

POR and use the following equation:

RAMP

POR

RAMP

GS th

()

If control of PWRGD active delay is the critical system param-

eter, then choose a value for

PWRGD and use the following

equation:

RAMP

PWRGD

RAMP

INT

−−

()

limit

Design Information, cont’d.

Auto-retry can be approximated as a

555-timer with 2.5µA charge up and

charge down currents through 8V, to

a count of 256. Therefore,

28 256

2.5 A

AUTORETRY

ramp

××

Due to the 2.5µA max charge current a resistor which draws

more than 2.5µA below 8V will disable the autoretry. Try to

keep this resistor as big as possible, e.g. 2.5MΩ, for most

MOSFETs with max V

t of 4V this will vary the 10µA Ramp

current source by only 4/2.5MΩ=1.6µA.

2.5

µA

2.5

µA

ramp

e.g.

28 256

2.5 A

Ion = 16.4s

××

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