LM3464AMH datasheet(18/22 Pages) NSC

18 / 22 page

For V

RAIL(peak) = 150V, the maximum value of RDRx is:

And the minimum value of R

DRx is:

Thus, the value of R

DRx must be selected in the range:

To minimize power dissipation on the zener diodes, a stan-

dard 42.2k

Ω resistor can be used for the R

DRx. Because the

resistors, R

DRx are used to absorb the power being introduced

by the voltage difference between V

RAIL and VZx, the maxi-

mum power dissipation on every R

DRx equals to:

Thus, a standard 42.2k

Ω resistor with 0.25W power rating

(1206 package) and 1% tolerance can be used.

Calculating the Values of Z

IN and RIN:

Similar to the requirements of selecting the Zx and R

DRx, the

voltage at the VIN pin of the LM3464/64A is clamped to 75V

by a voltage clamping circuit consists of Z

IN and RIN. Because

the maximum operating and shut-down current (V

EN < 2.1V)

are 3mA and 700uA respectively, in order to ensure the volt-

age of the VIN pin is clamped close to 75V even when the

LM3464/64A is disabled, a 1.5W/75V zener diode CMZ5946B

from Central Semiconductor is used to ensure adequate con-

duction current for Z

IN. The reverse current of the CMZ5946B

is specified 5mA at 75V, so the allowable current flows

through Z

IN is in between 5mA to 20mA.

The value of R

IN is governed by the following equations:

Maximum value of R

IN:

Minimum value of R

IN:

So the value of R

IN must be in the range:

To minimize power dissipations on both the Z

IN and RIN, a

standard 9.31k

Ω resistor can be selected for the R

IN. Then

the maximum power dissipation on R

IN is:

Thus, a standard 9.38k

Ω resistor with 2512 package (1W)

and 1% tolerance can be used.

LM3464AMH Datasheet(PDF) 18 Page - National Semiconductor (TI)

LM3464AMH Datasheet(HTML) 18 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Datasheet Download

Link URL