Application information

LNBH25LS

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DocID026753 Rev 3

circuit current protection either statically (simple current clamp) or dynamically by the PCL

bit of the I²C data 3 register. When the PCL (pulsed current limiting) bit LOW, the

overcurrent protection circuit works dynamically: as soon as an overload is detected, the

resumed and the OLF diagnostic bit is reset to LOW after a register reading is done.

operation can greatly reduce the power dissipation in short-circuit condition, still ensuring

excellent power-on startup in most conditions. However, there could be some cases in

which a highly capacitive load on the output may cause a difficult startup when the dynamic

protection is chosen. This can be solved by initiating any power startup 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 and register reading is done.

After the overload condition is removed, normal operation can be resumed in two ways,

according to the OLR I²C bit on the data 4 register.

If OLR=1, all VSEL 1..4 bits are reset to “0” and LNB output (VOUT pin) is disabled. To re-

enable output stage, the VSEL bits must be set again by the microprocessor, and the OLF

bit is reset to “0” after a register reading operation.

If OLR=0, output is automatically re-enabled as soon as the overload condition is removed,

and the OLF bit is reset to “0” after a register reading operation.

2.12

OTF: thermal protection and diagnostic

The LNBH25LS is also protected against overheating: when the junction temperature

exceeds 150 °C (typ.), the step-up converter and the linear regulator are shut off, the

diagnostic OTF bit in the status1 register is set to “1”. After the overtemperature condition is

removed, normal operation can be resumed in two ways, according to the THERM I²C bit

on the data 4 register.

If THERM=1, all VSEL 1..4 bits are reset to “0” and LNB output (VOUT pin) is disabled. To

re-enable output stage, the VSEL bits must be set again by the microprocessor, while the

OTF bit is reset to “0” after a register reading operation.

If THERM=0, output is automatically re-enabled as soon as the overtemperature condition

is removed, while the OTF bit is re

set to “0” after a register reading operation.