ST1S10 STMicroelectronics, ST1S10 Datasheet - Page 12

• Manufacturer Part Number: ST1S10
• Description: Monolithic synchronous step-down regulator
• Manufacturer: STMicroelectronics

Specifications of ST1S10

• Input Voltage Range: 2.5 V to 18 V
• Max Iout: 3 A
• High Internal Switching Frequency: 900 kHz
• Quiescent Current: < 6 μA in inhibit state

Application information
5.8.2
5.8.3
5.8.4
5.8.5
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Inhibit function
The inhibit pin can be used to turn OFF the regulator when pulled down, thus drastically
reducing the current consumption down to less than 6 µA. When the inhibit feature is not
used, this pin must be tied to V
proper operation, the signal source used to drive the inhibit pin must be able to swing above
and below the specified thresholds listed in the electrical characteristics section under V
Any slew rate can be used to drive the inhibit pin.
OCP (over-current protection)
The ST1S10 DC-DC converter is equipped with a switch over-current protection. In order to
provide protection for the application and the internal power switches and bonding wires, the
device goes into a shutdown state if the switch current limit is reached and is kept in this
condition for the T
(T
by cycle. Normal operation is resumed when no over-current is detected.
SCP (short circuit protection)
In order to protect the entire application and reduce the total power dissipation during an
overload or an output short circuit condition, the device is equipped with dynamic short
circuit protection which works by internally monitoring the V
In the event of an overload or output short circuit, if the V
feedback voltage (V
T
µs typ.). This operation is repeated cycle by cycle, and normal operation is resumed when
no overload is detected (V
This dynamic operation can greatly reduce the power dissipation in overload conditions,
while still ensuring excellent power-on startup in most conditions.
SCP and OCP operation with high capacitive load
Thanks to the OCP and SCP circuit, ST1S10 is strongly protected against damage from
short circuit and overload.
However, a highly capacitive load on the output may cause difficulties during start-up. This
can be resolved by using the modified application circuit shown in
minimum of 10 µF for C1 and a 4.7 µF ceramic capacitor for C3 are used. Moreover, for
C
divider resistor (R1) as shown in
Note that C4 may impact the control loop response and should be added only when a
capacitive load higher than 100 µF is continuously present. If the high capacitive load is
variable or not present at all times, in addition to C4 an increase in the output ceramic
capacitor C2 from 22 µF to 47 µF (or 2 x 22 µF capacitors in parallel) is recommended. Also
in this case it is suggested to further increase the input capacitors to a minimum of 10 µF for
C1 and a 4.7 µF ceramic capacitor for C3 as shown in
OFF
LOAD
ON(OCP)
time (T
> 100 µF, it is necessary to add the C4 capacitor in parallel to the upper voltage
= 22 µs typ.) under typical application conditions. This operation is repeated cycle
OFF(SCP)
OFF
FB
= 288 µs typ.) and turns on again for the T
period (T
) to drop below 0.3 V (typ.), the device goes into shutdown for the
FB
> 0.3 V typ.) for the full T
Doc ID 13844 Rev 4
OFF(OCP)
IN
Figure 3
to keep the regulator output ON at all times. To ensure
= 135 µs typ.) and turns on again for the T
The recommended value for C4 is 4.7 nF.
ON
Figure
OUT
period.
FB
voltage is reduced causing the
3.
(feedback voltage).
ON
Figure
period (T
3, in which a
ON(SCP)
ON
ST1S10
= 130
period
INH
.