a5975d STMicroelectronics, a5975d Datasheet - Page 33

• Manufacturer Part Number: a5975d
• Description: Up To 3 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

A5975D
This can be understood considering the inductor current ripple during the ON and OFF
phases:
●
Equation 29
●
Equation 30
where V
In short-circuit conditions, V
is very small, as equal to the voltage drop across parasitic components (typically the DCR of
the inductor and the V
to the inductor is maximized instead as approximately equal to V
So,
Equation 31
considering T
Equation 32
considering that f
In case a short-circuit at the output is applied, and V
controlled in most of the applications (see
short-circuit condition for an extended period, the external components (mainly the inductor
and diode) must be selected based on this value.
In case the V
does not compensate the current increase during T
example of a power-up phase with V
current escalates and the balance between
higher than the current limit. This must be taken into account in particular to avoid the risk of
an abrupt inductor saturation.
Equation 29
ON phase
OFF phase
D
is the voltage drop across the diode, DCR
Δ
I
L TOFF
IN
ON
is very high, it may happen that the ripple current during T
and
which has been already reduced to its minimum.
SW
Δ
=
I
L TON
has already been reduced to one third of the nominal.
30
–
------------------------------------------------------------- - 3 T
FW
(
V
Δ
in overcurrent conditions can be simplified to:
D
I
L TON
of the free-wheeling diode), while during T
+
=
Δ
OUT
I
V
L TOFF
V
----------------------------------------------------------------- - T
out
Doc ID 018760 Rev 1
IN
=
L
–
is negligible, so during T
+
(
V
------------------------------------------------------------------------------------- - T
DCR
DCR
IN
=
IN
–
–
------------------------------------------------------------- - T
(
V
L
L
= V
V
L
+
out
I ⋅
D
R
)
Figure
+
IN MAX
(
–
DS(on)
V
Equation 31
(
DCR
⋅
out
L
L
SW
+
) I ⋅
19). When the application must sustain the
= 36 V, where
L
DCR
)
(
+
ON
L
≅
IN
R
is the series resistance of the inductor.
–
------------------------------------------------------------- - 12μs
ON MIN
(Equation
(
DS(on)
L
= 12 V, the inductor current is
V
I ⋅
OFF
D
and occurs at a current slightly
)
+
(
)
) I ⋅
V
≅
the voltage across the inductor
OFF
out
V
-------- - 250ns
(
L
L
IN
Δ
)
+
31).
IN
ON
IL TON
(
DCR
Application information
.
)
ON
Figure 21
, the voltage applied
L
>
I ⋅
)
OFF
Δ
)
(
IL TOFF
(Equation
shows an
)
so the
33/50
32)