PI2125 datasheet(16/20 Pages) VICOR

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RUV

)

(

Set

value based on system allowable current

RUV

100

≥

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

)

(

)

(

Where:

)

(

: OV threshold voltage

ROV

current.

Typical Application Example 1:

Requirement:

Redundant Bus Voltage = 12V

Load Current = 10A (assume through each

redundant path)

Maximum Ambient Temperature = 70°C; no air flow

Auxiliary Voltage = 24V±10% (21.6V to 26.4V).

Solution:

A single PI2125 for each redundant 12V power

source should be used. Vin is 12V which is higher

than the SP pin maximum voltage rating of 8V, so

the PI2125 should be configured in the floating

configuration as shown in Figure 23.

PI2125 is

floated on Vin by connecting it’s GND pin and the

low side of the VC coupling capacitor to Vin.

Vaux:

Make sure that the Vaux voltage is always

higher than Vin (dc-dc converter output) by 6.0V to

ensure that the internal MOSFET is fully enhanced.

Since the auxiliary voltage is higher than the PI2125

VC clamp voltage a bias resistor (Rbias) is needed

in series with the VC pin.

Rbias value:

−

Rbias

or 1.43KΩ

Rbias Power dissipation rating

Rbias

)

(

−

Based on the resultant power dissipation on the bias

resistor, use a ¼W rated resistor.

SP and SN pins:

Since the PI2125 is floating, the

GND pin and S pin are connected to Vin, so connect

the SP pin directly to the PI2125 GND pin to reduce

the effect of parasitics between the SP pin and the

GND pin. This will avoid negative voltages on the SP

pin with respect to the GND pin. Connect SN to the

D pin.

BK pin:

Connect the BK pin to the GND pin to

achieve the minimum reverse current response time

SL pin: Not required, so leave floating

Fault pin

: The FT pin output is referenced to the

PI2125 GND pin which is connected to Vin. A level

shift circuit can be added to make FT output

referenced

the

system

ground.

The

recommended level shift circuit is shown in Figure

23. The level shift circuit uses a Dual Bias Resistor

Picor Corporation • picorpower.com

PI2125

Rev 1.0

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