Application information (valid for each section A/B)

LNBH26L

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Doc ID 022876 Rev 1

2.9

PNG: input voltage minimum detection

When input voltage (VCC pin) is lower than LPD (low power diagnostic) minimum

thresholds, the PNG I²C bit is set to “1”. Refer to the electrical characteristics table for

threshold details.

2.10

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. It is possible to

set the short-circuit current protection 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 lo LOW, the overcurrent protection circuit works dynamically: as soon as

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

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

dissipation in short-circuit condition, while still ensuring 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 done.

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

2.11

OTF: thermal protection and diagnostic

The LNBH26L 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.

To re-enable the output stages, 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, 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.