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
P_(pk)
FIGURE 19A
t₁
t₂
DUTY CYCLE, D = t₁/t₂
D CURVES APPLY FOR POWER
PULSE TRAIN SHOWN
READ TIME AT t₁ (SEE AN–569)
Z_θJA(t) = r(t) • R_θJA
T_J(pk) – T_A = P_(pk) Z_θJA(t)
5.0 10 20 50 100 200
t, TIME (ms)
500 1.0Ăk 2.0Ăk 5.0Ăk 10Ăk 20Ăk 50Ăk 100Ăk
Figure 19. Thermal Response
10⁴
DESIGN NOTE: USE OF THERMAL RESPONSE DATA
V_CC = 30 Vdc
10³
A train of periodical power pulses can be represented by the
model as shown in Figure 19A. Using the model and the de-
10²
I_CEO
vice thermal response the normalized effective transient ther-
mal resistance of Figure 19 was calculated for various duty
10¹
cycles.
To find Z_θJA(t), multiply the value obtained from Figure 19
10⁰
I_CBO
by the steady state value R_θJA.
AND
Example:
10^-1
I_CEX @ V_BE(off) = 3.0 Vdc
The MPS3904 is dissipating 2.0 watts peak under the follow-
ing conditions:
10^-2
t₁ = 1.0 ms, t₂ = 5.0 ms. (D = 0.2)
-40 -20 0 +20 +40 +60 +80 +100 +120 +140 +160 _{Using Figure 19 at a pulse width of 1.0 ms and D = 0.2, the}
T_J, JUNCTION TEMPERATURE (°C)
reading of r(t) is 0.22.
Figure 19A.
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
200
100
60
40
20
10
6.0
4.0
2.0
1.0 ms ^{100 µs}
T_C = 25°C
T_A = 25°C
dc
10 µs
1.0 s
dc
T_J = 150°C
CURRENT LIMIT
THERMAL LIMIT
SECOND BREAKDOWN LIMIT
4.0 6.0 8.0 10
20
V_CE, COLLECTOR-EMITTER VOLTAGE (VOLTS)
The safe operating area curves indicate I_C–V_CE 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 T_J(pk) = 150°C; T_C or
T_A is variable depending upon conditions. Pulse curves are
valid for duty cycles to 10% provided T_J(pk) ≤ 150°C. T_J(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.
40
Figure 20.
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