FUJITSU MB39A104 - Manual (Page 25)

MB39A104
25
The above power dissipation figures for the TPC8102 are satisfied with ample margin at 2.4 W (Ta
= +25 °C) .
CH2
Input voltage V
IN
(
Max
) = 19 V output voltage V
O
= 3.3 V, drain current I
D
= 3 A, Oscillation frequency
f
OSC
= 500 kHz, L = 15 µH, drain-source on resistance R
DS
(
ON
) := 50 m Ω, tr = tf := 100 ns.
Drain current (Max) : I
D
(
Max
)
Drain current (Min) : I
D
(
Min
)
P
C
= I
D
2 × R
DS
(
ON
)
× Duty
= 3 2 Ч 0.05 Ч 0.263
:= 0.118 W
P
S
(
ON
) =
V
D
(
Max
)
× I
D
× tr × f
OSC
6
=
19
Ч 3 Ч 100 Ч 10 −9 Ч 500 Ч 10
3
6
:= 0.475 W
P
S
(
OFF
)
=
V
D
(
Max
) × I
D
(
Max
) × tf × f
OSC
6
=
19 Ч 3.25 Ч 100 Ч 10 −9 Ч 500 Ч 10 3
6
:= 0.515 W
P
T
= P
C
+ P
S
(
ON
) + P
S
(
OFF
)
:= 0.118
+ 0.475 + 0.515
:= 1.108 W
I
D
(
Max
) = I
O
+
V
IN
− V
O
ton
2L
= 3 +
19 − 3.3
Ч
1
Ч 0.174
2
Ч 15 Ч 10 −6 500
Ч 10
3
:= 3.18 (A)
I
D
(
Min
) = I
O
−
V
IN
− V
O
ton
2L
= 3 −
19
− 3.3
Ч
1
Ч 0.174
2
Ч 15 Ч 10 −6 500
Ч 10 3
:= 2.82 (A)