SC1112TSTRT Semtech, SC1112TSTRT Datasheet - Page 18

• Manufacturer Part Number: SC1112TSTRT
• Manufacturer: Semtech

Specifications of SC1112TSTRT

• Lead Free Status / RoHS Status: Compliant

Short Circuit Protection
The VTT short circuit protection feature of the SC1112
is implemented by using the R
the output current increases, the regulation loop main-
tains the output voltage by turning the FET on more and
more. Eventually, as the R
FET will be unable to turn on any further, and the output
voltage will start to fall. When the VTT output voltage falls
to approximately 700mV, the LDO controller is latched off,
setting output voltage to 0V. Power must be cycled to re-
set the latch.
To prevent false latching due to capacitor inrush currents
or low supply rails, the current limit latch is initially
disabled. It is enabled once the short circuit delay time
has elapsed. Timing diagram on pages 4 to 5 will show a
detailed operation of the Short Circuit protection circuitry.
To be most effective, the MOSFET R
selected artificially low. The MOSFET should be
chosen so that at maximum required current, it is almost
fully turned on. If, for example, a supply of 1.5V at 4A is
required from a 3.3V ± 5% rail, the maximum allowable
R
To allow for temperature effects 200m
suitable room temperature maximum, allowing a peak
short circuit current of approximately 15A for a short time
before shutdown.
Capacitor Selection
Output Capacitors: Low ESR aluminum electrolytic or tan-
talum capacitors are recommended for bulk
capacitance, with ceramic bypass capacitors for decoupling
high frequency transients.
Input Capacitors: Placement of low ESR aluminum
electrolytic or tantalum capacitors at the input to the
MOSFET (VTTIN) will help to hold up the power supply
during fast load changes, thus improving overall transient
response. The +5VSTBY supply should be bypassed with a
10µF ceramic capacitor.
R
Applications Infomation (Cont.)
POWER MANAGEMENT
DS(ON)
DS
2006 Semtech Corp.
(
ON
)(
would be:
MAX
)
. 0
95
3
3 .
4
1
5 .
DS(ON)
. 1
025
limit is reached, the MOS-
DS(ON)
400
of the MOSFET. As
DS(ON)
m
should not be
would be a
18
Layout Guidelines
One of the advantages of using the SC1112 to drive an
external MOSFET is that the bandgap reference and
control circuitry do not need to be located right next to the
power device, thus a very accurate output voltage can be
obtained since heating effects will be minimal.
The 0.1µF bypass capacitor should be located close to the
+5VSTBY supply pin, and connected directly to the ground
plane. The ground pin of the device should also be con-
nected directly to the ground plane. The sense or adjust
pin does not need to be close to the output voltage plane,
but should be routed to avoid noisy traces if at all pos-
sible.
Power dissipation within the device is practically
negligible, requiring no special consideration during
layout.
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