PI2121 datasheet(16/21 Pages) VICOR

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Picor Corporation • picorpower.com

PI2121

Rev. 1.2 Page 16 of 21

Typical Application Example 1:

Requirement:

Redundant Bus Voltage = 3.3V

Load Current = 20A (assume through each

redundant path)

Maximum Ambient Temperature = 60°C, no air flow

Auxiliary Voltage = 12V (10V to 14V)

Solution:

A single PI2121 for each redundant 3.3V power

source should be used, configured as shown in the

circuit schematic in Figure 22.

Vaux:

Since the Vaux voltage does not exceed the VC pin

clamp voltage, connect the Vaux directly to the VC

SP and SN pins:

Connect each SP pin to the S pins and each SN pin

to the D pins

BK pin:

Connect the BK pin to ground to achieve the

minimum reverse current response time.

SL pin: Not required, so leave floating

FT pin:

Connect to the logic input and to the logic power

supply via a 10KΩ resistor.

Program UV and OV to monitor input voltage:

Program UV at 3.0V and OV at 3.6V

Use the three-resistor divider configuration:

200

500

or 2.49kΩ 1%

⎟

⎠

⎞

⎜

⎝

⎛

−

498

or 499Ω 1%

()

⎟

⎠

⎞

⎜

⎝

⎛

−

500

499

or 15kΩ 1%

Power Dissipation and Junction Temperature:

First use Figure 13 (Junction Temperature vs. Input

Current) to find the final junction temperature for 20A

load current at 60°C ambient temperature. In Figure

13 (illustrated in Figure 21) draw a vertical line from

20A to intersect the 60°C ambient temperature line.

At the intersection draw a horizontal line towards the

Y-axis

(Junction

Temperature).

The

Junction

Temperature at full load current (20A) and 60°C

ambient is 118°C.

Rds(on) is 2.0mΩ maximum at 25°C and will

increase as the Junction temperature increases.

From Figure 11, at 118°C Rds(on) will increase by

~35%, then

∗

Rds

)

(

maximum at 118°C

Maximum power dissipation is:

Rds

Iin

)

(

)

(

max

∗

Recalculate TJ:

⎟

⎠

⎞

⎜

⎝

⎛

∗

118

)

(

max

Figure 21: Example 1 final junction temperature at

20A/60°C TA

Reverse Current Threshold:

The following procedure demonstrates how to

calculate the minimum required reverse current in

the internal MOSFET to generate a reverse fault

condition and turn off the internal MOSFET.

At room temperature (25°C) typical Rds(on):

Rds

reverse

Vth

reverse

)

(

−

At maximum junction temperature (118°C) and

maximum Rds(on):

Rds

reverse

Vth

reverse

)

(

−

END OF LIFE

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