ST1S14 STMicroelectronics, ST1S14 Datasheet - Page 25

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

ST1S14
7.4
Example:
R
125 °C. We can consider a value of 0.3 Ω.
T
I
The overall losses are:
Equation 27
The junction temperature of device will be:
Equation 28
Where T
ambient. Considering that the device is mounted on board with a good ground plane, that it
has a thermal resistance junction-to-ambient (Rth
temperature of about 40 °C:
Short-circuit protection
In overcurrent protection mode, when the peak current reaches the current limit, the device
disables the power element and it is able to reduce the conduction time down to the
minimum value (approximately 90 nsec typical) to keep the inductor current limited. This is
the pulse by pulse current limitation to implement constant current protection feature.
For the ST1S14, the operation of the pulse by pulse current limitation depends on the FB
voltage:
●
●
In overcurrent condition, the duty cycle is strongly reduced and, in most applications, this is
enough to limit the switch current to the active current threshold, nominal or foldback
depending on the FB voltage.
Q
SW_EQ
DS(on)
has a typical value of 2 mA @ V
–
–
–
300 mV <V
current limitation value
V
kHz = 850 kHz/5) and the peak current value is foldback to 1.45A typical. The
frequency foldback helps to prevent the current diverging at low V
voltage. The current foldback reduces the stress of the embedded power element and
the external power components in case of persistent short circuit at the output.
FB
has a typical value of 0.2Ω @ 25 °C and increases to a maximum value of 0.4Ω @
A
is approximately 12 ns.
< 300mV: the switching frequency is decreased five times the nominal value (170
V
V
I
OUT
is the ambient temperature and Rth
OUT
IN
=
= 24 V
= 3 A
=5 V
P
0.3
FB
TOT
⋅
<1.22V: the device operates at nominal switching frequency and the
3 ( )
=
2
R
⋅
DSON
0.137
Doc ID 17977 Rev 1
⋅
+
(
I
24 3 12 10
T
OUT
T
J
IN
J
⋅
=
=
)
= 24 V.
2
⋅
T
40
⋅
A
D
+
+
⋅
+
Rth
1.15 40 86°C
V
IN
–
9
J-A
J A
⋅
⋅
–
⋅
I
850 10
OUT
is the thermal resistance junction-to-
J-A
⋅
P
≅
⋅
) of about 40 °C/W, and an ambient
TOT
⋅
T
SW
–
3
+
⋅
24 2 10
F
SW
⋅
+
⋅
V
Application information
IN
–
3
⋅
OUT
I
≅
Q
1.15W
=
""
/ high input
25/42