LNBH24LQTR Datasheet, PDF (7/25 Pages) STMicroelectronics – Dual LNBS supply and control IC with step-up and I²C interface

LNBH24L
Introduction
failure detected), set to LOW. The diagnostic bits are dedicated to the over-temperature and
over-load protections status (OTF and OLF).
2.9
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 is shut-
down for a time T_OFF, 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. When 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.
2.10
Thermal protection and diagnostic
The LNBH24L 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.)
2.11
Note:
Output current limit selection
The linear regulator current limit threshold can be set by an external resistor connected to
ISEL pin. The resistor value defines the output current limit by the equation:
Equation 1
I_MAX
[A]
=
10000
R_SEL
where R_SEL is the resistor connected between I_SEL and GND (see R2 in the typical
application circuit). The highest selectable current limit threshold is 0.9 A typ. with R_SEL= 11
kΩ. The above equation defines the typical threshold value for each output. However, it is
suggestible to not exceed for a long period a total amount of current of 1 A from both
sections (I_{OUT_A} + I_{OUT_B} < 1 A) in order to avoid the over temperature protection triggering.
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 bare use of this IC. NOTICE: DiSEqC™ is a trademark of EUTELSAT.
Doc ID 16857 Rev 2
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