HV312 Ver la hoja de datos (PDF) - Supertex Inc

Número de pieza

componentes Descripción

Fabricante

HV312

Sequencing Hotswap Controllers (Negative SupplyRail)

Supertex Inc 

Design Information

Programming Under and Over Voltage Shut Down

The UV and OV pins are connected to comparators with nominal

1.21V thresholds and 100mV of hysteresis (1.21V ± 50mV). They

are used to detect under voltage and over voltage conditions at the

input to the circuit. Whenever the OV pin rises above its high

threshold (1.26V) or the UV pin falls below its low threshold

(1.16V) the GATE voltage is immediately pulled low, the PWRGD

pin changes to its inactive state and the external capacitor

connected to the RAMP pin is discharged.

Calculations can be based on either the desired input voltage

operating limits or the input voltage shutdown limits. In the

following equations the shutdown limits are assumed.

The under voltage and over voltage shut down thresholds can be

programmed by means of the three resistor divider formed by R1,

R2 and R3. Since the input currents on the UV and OV pins are

negligible the resistor values may be calculated as follows:

UVOFF

=

VUVL

= 1.16

=

VEEUV(off)

× R2 + R3

R1 + R2 + R3

OVOFF

=

VOVH

= 1.26

=

VEEOV(off)

×

R3

R1 + R2 + R3

Where VEEUV(off) and VEEOV(off) are Under & Over Voltage Shut

Down Threshold points.

If we select a divider current of 100µA at a nominal operating input

voltage of 50 Volts then

R1 + R2 + R3 = 50V = 500kΩ

100uA

From the second equation for an OV shut down threshold of 65V

the value of R3 may be calculated.

OVOFF

= 1.26

=

65 × R3

500kΩ

R3 = 1.26 × 500KΩ = 9.69kΩ

65

The closest 1% value is 9.76kΩ

From the first equation for a UV shut down threshold of 35V the

value of R2 can be calculated.

UVOFF

=

1.16

=

35 × (R2 + R3)

500KΩ

R2 = 1.16 × 500kΩ − 9.76kΩ = 6.81kΩ

35

The closest 1% value is 6.81kΩ

Then

R1 = 500KΩ − R2 − R3 = 483kΩ

The closest 1% value is 487kΩ

HV302 / HV312

Under Voltage/Over Voltage Operation

From the calculated resistor values the OV and UV start up

threshold voltages can be calculated as follows:

UVON

=

VUVH

= 1.26

=

VEEUV(on)

× R2 + R3

R1 + R2 + R3

OVON

= VOVL

= 1.16

=

VEEOV(on)

×

R3

R1 + R2 + R3

Where VEEUV(on) and VEEOV(on) are Under & Over Voltage Start

Up Threshold points.

Then

VEEUV(on)

= 1.26 × R1 + R2 + R3

R2 + R3

VEEUV(on)

= 1.26 × 487kΩ + 6.81kΩ + 9.76kΩ

6.81kΩ + 9.76kΩ

= 38.29V

And

VEEOV(on)

= 1.16 × R1 + R2 + R3

R3

VEEOV(on)

= 1.16 × 487kΩ + 6.81kΩ + 9.76kΩ

9.76kΩ

= 59.85V

Therefore, the circuit will start when the input supply voltage is in

the range of 38.29V to 59.85V.

6

Rev. D

04/17/02

Supertex, Inc. 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 Fax: (408) 222-4895 www.supertex.com

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