Application information

LNBH23

8/32

2.11

Output current limit selection

The linear regulator current limit threshold can be set by an external resistor connected to

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

typically 900 ms. Simultaneously the diagnostic OLF I²C bit of the system register is set to

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

trademark of Philips Semiconductors.