HV312DB1 datasheet(2/2 Pages) SUTEX

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HV312DB1

Hotswap Controller

rev 2 12SEP02

Schematic

Inrush Limit

As supplied, the inrush current limit is set at 1 amp. To set

inrush limit to another value, please refer to the HV302/312

data sheet.

The circuit breaker trip point is set at 6.7 Amps. To set at a

different level, change R5 according to the following

equation:

100

ICB =

The power rating of R5 should be selected based on

maximum current during normal operation, which could be

just under the circuit breaker trip point.

100

Timing

Timing capacitor C1 determines start-up delay, rise time, and

circuit breaker retry interval,. Changing C1 will alter these

timings. Refer to the HV302/312 datasheet for the equations

that relate these timings to the value of C1. For use in the

equations, the nominal gate threshold voltage (VGS) of the

supplied IRFR3710 is 3V and transconductance is about 10

siemens.

Resistors R8, R9, and R10 set the delays for PWRGDs B, C,

and D according to the following equation:

Circuit Breaker Transient Immunity

The HV312 has built-in transient immunity of 2–5*s. To

increase transient immunity, an RC low-pass filter (R6C2)

may be placed on the SENSE input. (The demo board is

supplied with no filtering.)

Be aware that filtering the sense input will cause the inrush

current limit to overshoot at turn-on – the greater the filtering,

the greater the overshoot.

Undervoltage/Overvoltage Lockout

Resistors R1, R2, and R3 set the undervoltage and

overvoltage trip points. New trip points may be programmed

by changing the values of these resistors. Refer to the

HV302/312 data sheet for more information.

Additional Components

The RC network (R7C4) across the gate-source of the

external FET provides control loop compensation which

prevents inrush current peaking.

If the PWRGD A signal is used and experiences large

voltage swings, a 10nF capacitor should be installed at C5.

This limits dV/dt which may otherwise cause undesirable

coupling to internal circuits.

To defeat the circuit breaker auto-retry, install a 2.4M

resistor at location R4.

For servo-mode inrush control, remove C3. Inrush limit will

then be 3.3 Amps. See the HV302/312 data sheet for

details.

µF

487k

9.09k

not used

15m

121k

IRF3710S

not used

10nF

60.4k

R10

3.01k

100*F

VOUT+

VOUT-

VIN+

VIN-

HV312

VDD

RAMP

SENSE

GATE

PWRGDA

PWRGDB

PWRGDC

PWRGDD

not used

680pF

VEE

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