A5975ADTR STMicroelectronics, A5975ADTR Datasheet - Page 33

• Manufacturer Part Number: A5975ADTR
• Description: IC REG SW STEP-DOWN 2.5A 8SOIC
• Manufacturer: STMicroelectronics
• Series: -r
• Type: Step-Down (Buck), PWMr

Specifications of A5975ADTR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.235 V ~ 35 V
• Current - Output: 2.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 4 V ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-11425-2

A5975AD
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 instead maximized 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
slightly 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 could occur that the ripple current during T
, which has already been reduced to its minimum.
and
SW
Δ
=
I
L TON
has been already 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 018761 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)
Equation 31
V
(
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
(
DS(on)
L
(Equation
= 12 V, the inductor current is
V
and
I ⋅
OFF
D
)
+
(
)
) I ⋅
V
Equation 32
the voltage across the inductor
≅
OFF
out
V
-------- - 250ns
(
L
L
Δ
IN
)
+
IN
ON
31).
IL TON
(
DCR
Application information
.
ON
)
Figure 21
, the voltage applied
L
>
I ⋅
)
occurs at a current
OFF
Δ
)
(
IL TOFF
(Equation
shows an
)
, so the
33/50
32)