kh561 Fairchild Semiconductor, kh561 Datasheet - Page 12

• Manufacturer Part Number: kh561
• Description: Wideband, Low Distortion Driver Amplifier
• Manufacturer: Fairchild Semiconductor

I
I
P
P
P
DATA SHEET
with R
12
Note that the P
V
for a negative going V
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.
T
θ
T
T
The Limiting Factor for Output Power is Maximum
Junction Temperature
Reducing θ
airflow can greatly reduce the junction temperatures.
One effective means of heatsinking the KH561 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).
o
t
circuit
t
q
ca
c
j(t)
j(q)
=
o
=
= ⋅
. Absolute values of -V
=
total internal output stage current
power in hottest internal junction
prior
power in remainder of circuit [note V
= T
= 35°C/W for the KH561 with no heatsink in still air
1
V / R
I
= T
0
2
t
= T
o
.2 I
eq
output transistor junction temperature



A
=
(
hottest internal junction temperature
T
P
I
20°C/W
V
c
o
j(t)
t
⋅ ⋅
to to output stage
c
1.3 V
+ (P
=
CC
+ P
t
+
eq
+ P
R
(
⋅
L
−
V
total output current
q
t
I
q
o
CC
ca
1.4 17.3
CC
•
+ P
2
Figure 10: Thermal Model
•
20°C/W



t
200°C/W
R A
+
A
and P
−
⋅
−
through either heatsinking and/or
T
(
L
( )
f
V
2 I
.06
T
P
+ P
200°C/W
−
o
⋅ −
j(q)
q
L
1
−
t



q
2
o
circult
Ω
0.7 15.3
total load
. since we are only interested in



I
equations are written for positive
o
⋅
I output stage power
CC
t
+
−
)
)
19.2mA
, V
•
θ
T
o
ca
P
ca
c
, and I
Ω
circuit
Case Temperature
of 24°C in still air using
⋅
Case Temperature
I
)
t
θ
)
−
ca
CC
P
o
t
, should be used
Case to Ambient
Termal Impedance
T
Ambient
Temperature
−
= −
A
P
| V
q
CC
|]
R
I
I
P
P
P
From this, the hottest internal junctions may be found as
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 50Ω load.
Note that 1/2 of the total P
With these powers and T
T
T t
T q
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 KH561’s short circuiting capability is principally a
thermal issue. Generally, the KH561 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
resistance, R
Evaluation Board
An evaluation board (part number 730019) for the KH561
is available.
o
T
T
q
circuit
c
j
j
eq
( )
( )
=
=
=
=
=
2.5V / 45.6
=
prior to output stage
1
total power in both sides of hottest
case temperature
0.
=
68.1mA 15 2.5 0.7 15.3
total power in both sides of the output stage
25 C
=
2
50
power in the remainder of circuit
94 C
2 68.1mA 15 1.4 17.3
−



=
hottest internal junction
94 C
° +
54.9mA
⋅
733mW 169mW 1.058W
1.3 15
Ω
° +
° +
(
⋅
(

 
( )
.733 .169 1.058 35 94 C
[
410
1
x
1
2
, as shown in Figure 9.
2
5 1
Ω
+
(
−
(
−
⋅
.733 20 101
−
Ω
)
[
.169 200 111 C
+
[
2 68.1mA 54.9mA 19.2mA
=
⋅
(
⋅
54.9mA
5
54.9mA
−
)
)

 
−
⋅
⋅
=
+
A
45.6
−
=
=
=
−
=
)
25 C and
2
−
T
Ω
+
°
)
and P
°
Ω
( )
⋅
C C output stage
.06
Ω
°
⋅
68.1mA
⋅
=
68.1mA
2
θ
a

 =

junctions
junctions
+
ca
powers were used
°
REV. 1A February 2001
68.1mA
=
]
35 C / W
]
=
=
169mW
°
733mW
]
KH561