Datasheet

Application information LNBH23
8/32 Doc ID 13356 Rev 8
2.11 Output current limit selection
The linear regulator current limit threshold can be set by an external resistor connected to
I
SEL
pin. The resistor value defines the output current limit by the equation:
I
MAX
[A] = 10000/R
SEL
where R
SEL
is the resistor connected between I
SEL
and GND. The highest selectable current
limit threshold is 1.0 A typ with R
SEL
=10 kΩ. The above equation defines the typical
threshold value.
2.12 Over-current and short circuit protection and diagnostic
In order to reduce the total power dissipation during an overload or a short circuit condition,
the device is provided with a dynamic short circuit protection. It is possible to set the short
circuit current protection either statically (simple current clamp) or dynamically by the PCL
bit of the I²C SR. When the PCL (pulsed current limiting) bit is set lo LOW, the over current
protection circuit works dynamically: as soon as an overload is detected, the output current
is provided for 90 ms (typ.), after that the output is set in shut-down for a time T
OFF
of
typically 900 ms. Simultaneously the diagnostic OLF I²C bit of the system register is set to
"1". After this time has elapsed, the output is resumed for a time T
ON
=1/10 T
OFF
= 90 ms
(typ.). At the end of T
ON
, if the overload is still detected, the protection circuit will cycle again
through T
OFF
and T
ON
. At the end of a full T
ON
in which no overload is detected, normal
operation is resumed and the OLF diagnostic bit is reset to LOW. Typical T
ON
+T
OFF
time is
990 ms and an internal timer determines it. This dynamic operation can greatly reduce the
power dissipation in short circuit condition, still ensuring excellent power-on start-up in most
conditions. However, there could be some cases in which a highly capacitive load on the
output may cause a difficult start-up when the dynamic protection is chosen. This can be
solved by initiating any power start-up in static mode (PCL=1) and, then, switching to the
dynamic mode (PCL=0) after a chosen amount of time depending on the output
capacitance. Also in static mode, the diagnostic OLF bit goes to "1" when the current clamp
limit is reached and returns LOW when the overload condition is cleared.
2.13 Thermal protection and diagnostic
The LNBH23 is also protected against overheating: when the junction temperature exceeds
150 °C (typ.), the step-up converter and the liner regulator are shut-off, and the diagnostic
OTF SR bit is set to "1". Normal operation is resumed and the OTF bit is reset to LOW when
the junction is cooled down to 135 °C (typ.).
Note: 1 External components are needed to comply to bidirectional DiSEqC™ bus hardware
requirements. Full compliance of the whole application with DiSEqC™ specifications is not
implied by the use of this IC. NOTICE: DiSEqC™ is a trademark of EUTELSAT. I²C is
trademark of Philips Semiconductors.