HV311 データシートの表示（PDF） - Supertex Inc

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HV311

35-65V hotswap, controller with circuit breaker

Supertex Inc 

Design Information, cont’d.

These equations assume that the load is purely capacitive and

the following definitions apply.

CRAMP is the external capacitor connected to the RAMP pin.

IRAMP is the output current from the RAMP pin, nominally

10µA, when the voltage drop on RSENSE resistor is zero.

VINT is the internally regulated supply voltage and can range

from 8.5V to 12V.

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

transistor and may be obtained from its datasheet.

VGS(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.

gfs is the transconductance of the external pass transistor

and may be obtained from its datasheet.

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

ILIMIT 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

CRAMP for the most critical system performance characteristics.

For maximum contact bounce duration protection choose a

value for tPOR and use the following equation:

CRAMP

=

tPOR × IRAMP

2.4 + VGS(th)

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

eter, then choose a value for tPWRGD and use the following

equation:

CRAMP

=

tPWRGD × IRAMP

VINT − VGS(limit) − 1.2

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 VEE 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.

Auto-retry can be approximated as a

555-timer with 2.5µA charge up and

2.5µA

charge down currents through 8V, to

a count of 256. Therefore,

2.5µA

Cramp

TAUTORETRY

=

2

× 8 × 256

2.5µA

×

Cramp

e.g. 2 × 8 × 256 × Ion = 16.4s

2.5µA

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 Vt of 4V this will vary the 10µA Ramp

current source by only 4/2.5MΩ=1.6µA.

8

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