M5451 datasheet(6/8 Pages) STMICROELECTRONICS

6 / 8 page

POWER DISSIPATION OF THE IC

The power dissipation of the IC can be limited using

different configurations.

a) In the application R must be chosen taking into

account the worst operating conditions.

VOUT

+V C

R is determined by the maximum number of seg-

ments activated

R =

− VD MAX − VO MIN

NMAX

⋅ ID

The worst case condition for the device is when

roughly half of the maximum number of segments

are activated.

It must be checked that the total power dissipation

does not exceed the absolute maximum ratings of

the device.

In critical cases more resistors can be used in

conjunction with groups of segments.

In this case the current variation in the single

resistor is reduced and Ptot limited.

b) In this configuration the drop on the serial con-

+V C

+VC

VOUT +VD

nected diodes is quite stable if the diodes are

properly chosen.

The total power dissipation of the IC depends, in a

first approximation, only on the number of seg-

ments activated.

c) In this configuration VOUT + VD is constant. The

total power dissipation of the IC depends only on

the number of segments activated.

M5450 - M5451

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