Typical application Example 1:

Picor Corporation • picorpower.com

PI2003

Rev 1.0

Requirement:

Redundant Bus Voltage = -48V (-36V to -60V, 100V

for 100ms transient)

Load Current = 5A load (assume through each

redundant path)

Maximum Ambient Temperature = 60°C

Solution:

A single PI2003 with a suitable MOSFET for each

redundant -48V power source should be used and

configured as shown in figure 13. The VC is biased

from the return line through a bias resistor.

Select a suitable N-Channel MOSFET:

Select the

N-Channel MOSFET with voltage rating higher than

the input voltage, Vin, plus any expected transient

voltages, with a low Rds(on) that is capable of

supporting the full load current with margin. For

instance, a 100V rated MOSFET with 10A current

capability is suitable.

An exemplary MOSFET

having these characteristic is Si4486EY from Vishay

Siliconix.

From Si4486EY datasheet:

•

N-Channel MOSFET

•

•

•

± 20V

•

•

Reverse current threshold is:

mA

m

mV

on

Rds

reverse

Vth

reverse

Is

300

20

6

)

(

.

.

−

=

Ω

−

=

=

Power dissipation:

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

increase as the temperature increases. Add 40°C to

maximum ambient temperature to compensate for

the temperature rise due to power dissipation. At

100°C (60°C + 40°C) Rds(on) will increase by 63%.

Ω

=

∗

Ω

=

m

m

on

Rds

41

63

.

1

25

)

(

maximum at 100°C

Maximum Junction temperature

C

m

A

W

C

C

T

J

°

=

⎟

⎠

⎞

⎜

⎝

⎛

Ω

∗

∗

°

+

°

=

111

41

)

0

.

5

(

50

60

2

max

Recalculate based on calculated Junction

temperature, 115°C.

At 115°C Rds(on) will increase by 72%.

Ω

=

∗

Ω

=

m

m

on

Rds

43

72

.

1

25

)

(

maximum at 115°C

C

m

A

W

C

C

T

J

°

=

⎟

⎠

⎞

⎜

⎝

⎛

Ω

∗

∗

°

+

°

=

113

43

)

0

.

5

(

50

60

2

max

A

K

V

R

VC

I

FT

Sink

FT

μ

92

120

0

.

11

=

Ω

=

=

−

VC:

Connect each controller to the return path with

a separate bias resistor, Rbias.

Sink

FT

clampMax

I

IC

VC

Vbus

Rbias

−

+

−

=

max

min

Ω

=

+

−

=

K

mA

mA

V

V

Rbias

47

.

11

092

.

0

0

.

2

12

36

, or 11.5KΩ,

1%

input voltage and minimum clamp voltage.

mW

K

V

V

Rbias

VC

Vbus

Pd

clampMIN

Rbias

200

5

.

11

)

12

60

(

)

(

2

2

max

=

Ω

−

=

−

=

Figure 13:

PI2003 in low side -48V application.