ST1S14 STMicroelectronics, ST1S14 Datasheet - Page 26

• Manufacturer Part Number: ST1S14
• Description: Up to 3 A step down switching regulator
• Manufacturer: STMicroelectronics

Application information
7.4.1
26/42
The inductor current ripple during ON and OFF phases can be written as:
●
Equation 29
●
Equation 30
where V
The pulse by pulse current limitation is effective to implement constant current protection
when:
Equation 31
The overcurrent protection is operating over the entire output voltage, which goes from the
regulated output voltage (V
output.
From
current protection becomes more critical the lower is the V
In fact, the voltage applied to the inductor during the OFF time becomes equal to the voltage
drop across parasitic components (typically the DCR of the inductor and the V
wheeling diode) when VOUT is negligible, while during T
is maximized and it is approximately equal to V
heavy short-circuit at the output with maximum input voltage.
300 mV < V
The nominal output voltage can be written as:
Equation 32
From
Equation 33
so the output voltage is:
ON phase
OFF phase
Equation 29
Equation 32
D
is the voltage drop across the diode, DCR
FB
< 1.22 V
and
the voltage can be expressed as:
Δ
Equation 30
I
L TON
V
Δ
O_SET
I
O_SET
L TON
Doc ID 17977 Rev 1
=
V
--------------------------------------------------------------------------------------- - T
) down to GND during heavy short circuit applied at the
=
=
IN
we can gather that the implementation of the constant
V
–
----------------------------------------------------------------- - T
–
Δ
⎛
⎝
(
FB
1
I
V
V
L TON
OUT
D
+
⋅
+
⎛
⎝
R
------ -
R
1
1
2
V
–
⎞
⎠
+
OUT
=
(
R
------ -
R
=
DCR
L
IN
1
2
L
Δ
⎞
⎠
V
------------------ -
+
I
. In general the worst case scenario is
1.22
L TOFF
O_SET
=
DCR
L
L
+
1.22
is the series resistance of the inductor.
R
L
DSON
I ⋅
ON
⋅
⎛
⎝
)
OUT
1
(
the voltage applied the inductor
) I ⋅
+
OFF
R
------ -
R
and the higher is V
(
1
2
⎞
⎠
)
ON
)
FW
of the free
IN
ST1S14
.