HV311_09 datasheet(7/17 Pages) SUTEX

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HV311

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Startup Timer

The startup timer limits the startup to 100ms. Should there

be an overload or short circuit during startup, then the exter-

nal pass transistor will carry current for no more than 100ms.

Upon tripping of the timer the RAMP and GATE voltages

reset to zero, and the autoretry timer starts if enabled.

Circuit Breaker

The circuit breaker trips in less than 5.0μs when the voltage

across the sense resistor reaches 100mV. Upon tripping of

the circuit breaker the RAMP and GATE voltages reset to

zero, and the autoretry timer starts if enabled.

Autoretry Timer

The retry interval is determined by charging and discharg-

ing the C

RAMP capacitor 256 times. One cycle corresponds to

charging of C

RAMP to 8.0V with a current of 2.5μA, and subse-

quent discharging to zero with a current of 2.5μA. Hence:

CHARGE · tCYCLE = CRAMP · 2 · ΔV

CYCLE = (10n)(2)(8)/(2.5μ)

CYCLE = 64ms

AUTORETRY = (256)(64m)

AUTORETRY = 16.4s

The autoretry timer can be disabled by adding a resistor at

the RAMP pin. A resistor which keeps the RAMP voltage

from rising to 8.0V will keep the timer from counting. This

can accomplished by adding a resistor at the RAMP pin with

a value of about 2.5MΩ. Note that this resistor forms an ad-

ditional load during the startup, thereby causing the time in-

tervals to increase somewhat.

•

Kelvin Connections

In order to make an accurate measurement of power supply

current it is advisable to make use of Kelvin connections.

The idea is to not incur voltage drops in the sense leads due

to the main power supply current. See diagram below.

Paralleling External MOSFETs

Equal current sharing may not be achievable due to the tol-

erance issues with the threshold voltage and gain charac-

teristics of the MOSFETs. Paralleling of devices is not rec-

ommended. The issues with paralleling can be alleviated by

using resistor ballasting.

For this application the HV311 with active low PWRGD is

recommended where the PWRGD pins of multiple hot swap

circuits can be connected in a wired OR conﬁguration.

To Negative

Terminal of

Power Source

To Source

of MOSFET

Sense Resistor

SENSE

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