DATA SHEET

KH563

12

REV. 1A January 2008

Figure 10: Thermal Model

delta V’s. For bipolar swings, the two powers for each

output polarity are developed as shown above then

ratioed by the duty cycle. Having the total internal power,

as well as its component parts, the maximum junction

temperature may be computed as follows.

θ

θ

output transistor junction temperature

hottest internal junction temperature

The Limiting Factor for Output Power is Maximum

Junction Temperature

Reducing

θ

ca

through

either

heatsinking

and/or

airflow can greatly reduce the junction temperatures.

One effective means of heatsinking the KH563 is to use

a thermally conductive pad under the part from the pack-

age bottom to a top surface ground plane on the compo-

nent side. Tests have shown a

θ

a “Sil Pad” available from Bergquist (800-347-4572).

As an example of calculating the maximum internal junc-

tion temperatures, consider the circuit of Figure 1 driving

±2.5V, 50% duty cycle, square wave into a 50

Ω

load.

here since the 50% duty cycle output splits the power

evenly between the two halves of the circuit whereas the

total powers were used to get case temperature.

Even with the output current internally limited to 250mA,

the KH563’s short circuiting capability is principally a

thermal issue. Generally, the KH563 can survive short

duration shorts to ground without any special effort. For

protection against shorts to the ±15 volt supply voltages,

it is very useful to reduce some of the voltage across the

output stage transistors by using some external output

Evaluation Board

An evaluation board (part number 730019) for the KH563

is available.

R50 410 5

51 45.6

I 2.5V/ 45.6

eq

o

=

⋅

−







 =

=

()

Ω

Ω

Ω

Ω ==

=+







 =

54.9mA

I

54.9mA 54.9mA .06

T 12

P 68.1mA 15 2.5 0.7 15.3 68.1mA

⋅





Ω== 733mW

totalpower inboth sides of the output stagee

P 1 68.1mA 15 1.4 17.3 68.1mA 84.5

− −

⋅



=

0.

Ω

mmW

totalpower inboth sides of hottest junctions

prrior to output stage

P

1.3 15 2 68.1m

733mW 169mW 1.058W

powe

−+





−−

=

rr in the remainder of circuit

With these powers and TT 25C and

35C/W

T 25 C .733 .169 1.05

Aca

c

=°

= °

=° +

+ +

θ

8835 94 C

case temperature

From this, the hott

eest internal junctions may be found as

Tt 94 C

j

12

j

12

.733 20 101 C output stage

Tq 94 C

..0845 200 102 C

hottest internal junction

KH560

+

-

KH560 Fig 9

With:

Ambient

Temperature

θ

ca

200

°

C/W

20

°

C/W

Case Temperature

Case to Ambient

Termal Impedance

I V /R total output current

withR R RA

A

oo eq

eq L

fL

L

=

=

−−













=+

+

()









1 totalload

II I .06

t 12 oo2

=⋅ −

totalinternal output stage current

PI V

P.1 I V

t

qt C

−⋅

()

=⋅ ⋅

Ω

0

CCo

t

V 0.7 15.3 I

power inhottest internal j

−− −

⋅

()

Ω

uunction

prior to output stage

P1.3 V

circuit

CC

=⋅ ⋅ 22 I I 19.2mA P P

power inremainder of ci

to

t q

⋅− +

rrcuit [note V | V |]

CC

CC

=−