HV100(2013) Ver la hoja de datos (PDF) - Supertex Inc

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Fabricante

HV100
(Rev.:2013)

3-Pin Hotswap, Inrush Current Limiter Controllers (Negative Supply Rail)

Supertex Inc 

HV100

Application Information

Turn On Clamp

Hotswap controllers using a MOSFET as the pass element

all include a capacitor divider from VPP to VNN through

CLOAD, CRSS and CGS. In most competitive solutions a large

external capacitor is added to the GATE of the pass element

to limit the voltage on the GATE resulting from this divider. In

those instances, if a GATE capacitor is not used the internal

circuitry is not available to hold off the GATE, and therefore

a fast rising voltage input will cause the pass element to turn

on for a moment. This allows current spikes to pass through

the MOSFET.

The HV100 includes a built-in clamp to ensure that this spuri-

ous current glitch does not occur. The built-in clamp will work

for the time constants of most mechanical connectors. There

may be applications, however, that have rise times that are

much less than 1.0µs (100’s of ns). In these instances it may

be necessary to add a capacitor from the MOSFET GATE to

source to clamp the GATE and suppress this current spike.

In these cases the current spike generally contains very little

energy and does not cause damage even if a capacitor is not

used at the GATE.

the initial slope of the GATE voltage is approximately 2.5V/ms

regardless of the MOSFET, and the total hotswap period and

peak currents are a function of a MOSFET type dependent

constant multiplied by CLOAD.

Typically if MOSFETs of the same type are used, the hotswap

results will be extremely consistent. If different types are used

they will usually exhibit minimal variation.

Short Circuit Protection

The HV100 provides short circuit protection by shutting down

if the Miller Effect associated with hotswap does not occur.

Specifically, if the output is shorted then the GATE will rise

without exhibiting a “flat response”. Due to the fact that we

have normalized the hotswap period for any pass element, a

timer can be used to detect if the GATE voltage rises above

a threshold within that time, indicating that a short exists. The

diagram below shows a typical turn on sequence with the load

shorted, resulting in a peak current of 4A.

Auto-adapt Operation

The HV100 auto-adapt mechanism provides an important

function. It normalizes the hotswap period regardless of pass

element or load capacitor for consistent hotswap results. By

doing this it allows the novel short circuit mechanism to work

because the mechanism requires a known time base.

The maximum current that may occur during this period can

be controlled by adding a resistor in series with the source of

the MOSFET. The lower graph shows the same circuit with

a 100mΩ resistor inserted between source and VNN. In this

case the maximum current is 25% smaller.

The above diagram illustrates the effectiveness of the auto-

adapt mechanism. In this example three MOSFETs with dif-

ferent CISS and RDSON values are used. The top waveform is

the hotswap current, while the bottom waveform is the GATE

voltage. As can be seen, the hotswap period is normalized,

Doc.# DSFP-HV100

B060513

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Supertex inc.

www.supertex.com

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