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| 型號： | AB-039 |
| 英文描述： | POWER AMPLIFIER STRESS AND POWER HANDLING LIMITATIONS |
| 中文描述： | 功放應(yīng)力和功率限制 |
| 文件頁數(shù)： | 1/6頁 |
| 文件大小： | 52K |
| 代理商： | AB-039 |
APPLICATION BULLE TIN
Mailing Address: PO Box 11400 Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd. Tucson, AZ 85706
Tel: (602) 746-1111 Twx: 910-952-111 Telex: 066-6491 FAX (602) 889-1510 Immediate Product Info: (800) 548-6132
POWER AMPLIFIER STRESS
AND POWER HANDLING LIMITATIONS
BY BRUCE TRUMP (602) 746-7347
FIGURE 2. Safe Operating Area (SOA)— OPA502. (Figure 2 in PDS-1166)
SAFE OPERATING AREA
10
V
CE
|V
S
– V
OUT
| (V)
I
O
10
5.0
2.0
1.0
0.5
0.2
0.1
5
2
1
20
50
100
T
C
= +25°C
T
C
= +85°C
T
C
= +125°C
t 5s
t m
t m
Thermal Limitation
(T
J
= 200°C)
Second Breakdown
Limited
Max Current
Thermal
Limits
Second
Breakdown
Region
Voltage
Breakdown
To achieve reliable power amplifier designs you must con-
sider the stress on the amplifier compared to its power
handling limitations. Power handling limits are specified by
the Safe Operating Area (SOA) curves of the power amp.
Stress on the amplifier depends on amplifier load and signal
conditions which can be evaluated with straightforward
techniques.
Consider the simplified power op amp shown in Figure 1.
Output transistors Q
and Q
2
provide positive and negative
output current to the load. I
is shown flowing out of the
amplifier, so Q
is supplying the output current. For positive
output current, Q
2
is “off” and can be ignored.
The stress on Q
under load is related to the output current
and the voltage across Q
1
(its collector-to-emitter voltage,
V
CE
). The product of these quantities, I
OUT
V
CE
, is the power
dissipation of Q
. This power dissipation is one important
consideration, but the “safe operating area” provides a more
complete description of the amplifier’s limits.
SAFE OPERATING AREA
The power handling ability of a power transistor is charac-
terized by its Safe Operating Area (SOA), Figure 2. The
SOA curve shows permissible voltage, (V
CE
) and current,
(I
OUT
). The maximum safe current is a function of V
CE
. The
characteristic shape of this curve has four distinct regions.
At low V
, maximum output current can be safely delivered
to the load. Exceeding the maximum current in this region
can overstress wire bonds or metallization on the die and
destroy the device.
FIGURE 1. Simplified Power Op Amp Circuit.
As V
CE
is increased, the power dissipation of the transistor
increases until self-heating raises the junction temperature to
its maximum safe value. All points along this thermally
limited region (dotted lines) produce the same power dissi-
pation. V
I
is a constant 120W (at 25
°
C) in Figure 2. All
points on this region of the curve produce the same maxi-
mum junction temperature. Exceeding the safe output cur-
rent in this region may damage the transistor junction.
V
IN
V+
Q
1
Q
2
R
L
I
OUT
V
O
V
CE
= (V+) –V
O
V–
V
CE
–
+
R
F
R
I
1993 Burr-Brown Corporation
AB-039
Printed in U.S.A. April, 1993
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