MMBTA20LT1 Datasheet, PDF (6/8 Pages) Motorola, Inc – General Purpose Amplifier

MMBTA20LT1
1.0
0.7
0.5
D = 0.5
0.3
0.2
0.2
0.1
0.1
0.07
0.05
0.05
0.02
0.03
0.02
0.01
SINGLE PULSE
0.01
0.01 0.02 0.05 0.1 0.2 0.5 1.0 2.0
FIGURE 19A
DUTY CYCLE, D = t1/t2
P(pk)
D CURVES APPLY FOR POWER
PULSE TRAIN SHOWN
t1
READ TIME AT t1 (SEE AN–569)
t2
Z_θJA(t) = r(t) • R_θJA
TJ(pk) – TA = P(pk) Z_θJA(t)
5.0 10 20 50 100 200
t, TIME (ms)
500 1.0 k 2.0 k 5.0 k 10 k 20 k 50 k 100 k
Figure 19. Thermal Response
104
VCC = 30 Vdc
103
102
ICEO
101
100
ICBO
AND
10–1
ICEX @ VBE(off) = 3.0 Vdc
10–2
–4 –2
00
0 + 20 + 40 + 60 + 80 + 100 + 120 + 140 + 160
TJ, JUNCTION TEMPERATURE (°C)
Figure 19A.
DESIGN NOTE: USE OF THERMAL RESPONSE DATA
A train of periodical power pulses can be represented by the model
as shown in Figure 19A. Using the model and the device thermal
response the normalized effective transient thermal resistance of
Figure 19 was calculated for various duty cycles.
To find Z_θJA(t), multiply the value obtained from Figure 19 by the
steady state value R_θJA.
Example:
The MPS3904 is dissipating 2.0 watts peak under the following
conditions:
t1 = 1.0 ms, t2 = 5.0 ms. (D = 0.2)
Using Figure 19 at a pulse width of 1.0 ms and D = 0.2, the reading of
r(t) is 0.22.
The peak rise in junction temperature is therefore
∆T = r(t) x P(pk) x R_θJA = 0.22 x 2.0 x 200 = 88°C.
For more information, see AN–569.
400
1.0 ms ^{100 µs}
200
10 µs
100
TC = 25°C
1.0 s
60
dc
TA = 25°C
40
dc
20
TJ = 150°C
10
CURRENT LIMIT
6.0
THERMAL LIMIT
SECOND BREAKDOWN LIMIT
4.0
2.0
4.0 6.0 8.0 10
20
40
VCE, COLLECTOR–EMITTER VOLTAGE (VOLTS)
Figure 20.
The safe operating area curves indicate IC–VCE limits of the
transistor that must be observed for reliable operation. Collector load
lines for specific circuits must fall below the limits indicated by the
applicable curve.
The data of Figure 20 is based upon TJ(pk) = 150°C; TC or TA is
variable depending upon conditions. Pulse curves are valid for duty
cycles to 10% provided TJ(pk) ≤ 150°C. TJ(pk) may be calculated from
the data in Figure 19. At high case or ambient temperatures, thermal
limitations will reduce the power that can be handled to values less
than the limitations imposed by second breakdown.
6
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