9

Dissipation In Multiple Outputs

The HIP0080 and HIP0081 Power Drivers have multiple

MOS Output Drivers and require special consideration with

regard to maximum current and dissipation ratings. While

each output has a maximum current specification consistent

with the device structure, all such devices on the chip can

not be simultaneously rated to the same high level of peak

current. The total combined current and the dissipation on

the chip must be adjusted for maximum allowable ratings,

given simultaneous multiple output conditions.

For the HIP0081, the maximum positive output current rating

is 2.2A when one output is ON. When ALL outputs are ON,

the rating is reduced to 1.5A because the total maximum

current is limited to 6A. For any given application, all output

drivers on a chip may or may not have a different level of

loading. The discussion here is intended to provide relatively

simple methods to determine the maximum dissipation and

current ratings as a general solution and, as a special

solution, when all switched ON outputs have the same current

loading.

General Solution

A general equation for dissipation should specify that the

total power dissipation in a package is the sum of all

significant elements of dissipation on the chip. However, in

Power BiMOS Circuits very little dissipation is needed to

control the logic and predriver circuits on the chip. The

dissipation losses in each channel where the current, I is the

output current and the resistance, R is the NMOS channel

driver without regard to uniformity of dissipation in each

MOS channel. The dissipation loss in an NMOS channel is

given in Equation 2 where the current, I, is determined by the

output load when the channel is turned ON. The channel

gate voltage and the chip temperature. Other switching

the chip and bond wires of the package.

The temperature rise in the package due to the dissipation is

resistance,

θ

solution is:

or:

Since this solution relates only to the package, further

consideration must be given to a practical heat sink. The

equation of linear heat flow assumes that the thermal

resistance from Junction-to-Ambient (

θ

thermal resistance from Junction-to-Case and the thermal

resistance from Case (heat sink)-to-Ambient. The Junction-

to-Ambient thermal resistance,

θ

environment and can be expressed as:

FIGURE 4. SINGLE PULSE ENERGY TEST SHOWING THE

FAILURE BOUNDARY FOR EACH HIP0080

OUTPUT STRESSED TO POINT OF FAILURE

FIGURE 5. SINGLE PULSE ENERGY TEST SHOWING THE

FAILURE BOUNDARY FOR EACH HIP0081

OUTPUT STRESSED TO POINT OF FAILURE

0.1

1

10

100

1000

100

1000

10000

PULSE WIDTH TIME (ms)

HIP0080 SINGLE PULSE

SAFE

OPERA

TING

AREA

ENERGY vs TIME

NOTE: SAFE OPERATING AREA

BELOW DOTTED LINE

0.1

1

10

100

1000

100

1000

10000

PULSE WIDTH TIME (ms)

HIP0081 SINGLE PULSE

ENERGY vs TIME

NOTE: SAFE OPERATING AREA

BELOW DOTTED LINE

P

k

k1

=

n

∑

=

(EQ. 1)

P

k

I

2

r

DS ON

()

×

=

(EQ. 2)

T

J

T

C

P

D

θ

JC

×

+

=

(EQ. 3)

(EQ. 3A)

T

C

T

J

P

D

θ

JC

×

–

=

θ

JA

θ

JC

θ

CA

+

=

(EQ. 4)

HIP0080, HIP0081