STMicroelectronics Evaluation board for A5970AD EVALA5970AD EVALA5970AD Fiche De Données
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EVALA5970AD
DocID14661 Rev 5
25/42
A5970AD
Application information
42
Switching losses due to turning ON and OFF. These are derived using the following
equation:
equation:
Equation 23
Where T
RISE
and T
FALL
represent the switching times of the power element that cause the
switching losses when driving an inductive load (see
). T
SW
is the equivalent
switching time.
Figure 14. Switching losses
Quiescent current losses.
Equation 24
Where I
Q
is the quiescent current.
Example 2:
V
IN
= 12 V
V
OUT
= 3.3 V
I
OUT
= 0.8 A
R
DS(on)
has a typical value of 0.25 at 25 °C and increases up to a maximum value of 0.5. at
150 °C. We can consider a value of 0.4
.
T
SW
is approximately 70 ns.
I
Q
has a typical value of 2.7 mA at V
IN
= 12 V.
The overall losses are:
Equation 25
P
SW
V
IN
I
OUT
T
ON
T
OFF
+
2
------------------------------------
F
SW
V
IN
=
I
OUT
T
SW
F
SW
=
P
Q
V
IN
I
Q
=
P
TOT
R
DSON
I
OUT
2
D V
IN
I
OUT
T
SW
F
SW
V
IN
I
Q
=
+
+
=
0.4 0.8
2
0.3 12 0.8
70
10
9
–
500
10
3
12 2.7
10
3
–
+
+
0.55W
=