Application information (valid for each section

A/B)

LNBH26LS

10/33

DocID025504 Rev 1

For recommended DC-DC capacitor and inductor values refer to Section 5: "Typical

application circuits" and to the BOM in Table 5: "LNBH26LS DiSEqC 1.x bill of material" .

2.11

OLF: overcurrent and short-circuit protection and diagnostic

In order to reduce the total power dissipation during an overload or a short-circuit condition,

each section of the device is provided with a dynamic short-circuit protection. The short-

circuit current protection can be set either statically (simple current clamp) or dynamically

through the corresponding PCL bit of the I²C DATA3 register. When the PCL (pulsed

current limiting) bit is set to low, the overcurrent protection circuit works dynamically: as

the corresponding diagnostic OLF I²C bit of the STATUS1 register is set to “1”. After this

ms and is determined by an internal timer. This dynamic operation can greatly reduce the

power dissipation in short-circuit condition, ensuring an excellent power-on startup in most

conditions. However, there may be some cases in which a highly capacitive load on the

output can 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” (and the FLT pin is set

to low) when the current clamp limit is reached and returns low when the overload condition

is cleared and register reading is performed.

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

according to the OLR I²C bit on the DATA4 register.

If OLR=1, all VSEL bits, corresponding to the involved section, are reset to “0” and the LNB

set again by the microprocessor and the OLF bit is reset to “0” after a register reading

operation.

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

is removed, and th

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

2.12

OTF: thermal protection and diagnostic

The LNBH26LS is also protected against overheating: when the junction temperature

exceeds 150 °C (typ.), the step-up converter and both linear regulators 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 DATA4 register.

If THERM=1, all VSEL bits are reset to “0” and both LNB outputs (V

To re-enable the output stages, the VSEL bits must be set again by the microprocessor,

whil

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

If THERM=0, outputs are automatically re-enabled as soon as the overtemperature

condition is removed, while the OTF bit is reset to “0” after a register reading operation.