LNBH25 STMicroelectronics, LNBH25 Datasheet - Page 8

• Manufacturer Part Number: LNBH25
• Description: LNB supply and control IC with step-up and I2C interface
• Manufacturer: STMicroelectronics

Application information
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Surge protections and TVS diodes
The LNBH25 device is directly connected to the antenna cable in a set-top box. Atmospheric
phenomenon can cause high voltage discharges on the antenna cable causing damage to
the attached devices. Surge pulses occur due to direct or indirect lightning strikes to an
external (outdoor) circuit. This leads to currents or electromagnetic fields causing high
voltage or current transients. Transient voltage suppressor (TVS) devices are usually
placed, as shown in the following schematic, to protect the STB output circuits where the
LNBH25 and other devices are electrically connected to the antenna cable.
Figure 4.
For this purpose we recommend the use of LNBTVSxx surge protection diodes specifically
designed by ST. The selection of LNBTVS diodes should be made based on the maximum
peak power dissipation that the diode is capable of supporting (see Ppp (W) parameter in
the LNBTVS datasheet for further details).
FLT: fault flag
In order to get an immediate feedback on diagnostic status, LNBH25 is equipped with a
dedicated fault flag pin (FLT). In the case of overload (OLF bit=1) or overheating (OTF bit=1)
or if Power No Good (PNG bit=1) condition is detected, the FLT pin (open drain output) is set
to low and is kept low until the relevant activating diagnostic bit is cleared. Be aware that
diagnostic bits OLF, OTF and PNG, once activated, are kept latched to “1” until the cause
origin is removed and a new register reading operation is performed by the microprocessor.
The FLT pin must be connected to a positive voltage (5 V max.) by means of a pull-up
resistor.
VMON: output voltage diagnostic
When device output voltage is activated (V
long as the output voltage level is below the guaranteed limits, the VMON I²C bit is set to “1”.
See
TMON: 22 kHz tone diagnostic
The 22 kHz tone can be internally detected and monitored if the DETIN pin is connected to
the LNB output bus (see typical application circuit in
capacitor.
The tone diagnostic function is provided with the TMON I²C bit. If the 22 kHz tone amplitude
and/or the tone frequency is out of the guaranteed limits (see
set to “1”.
Table 17
Surge protection circuit
for more details.
Doc ID 022433 Rev 4
OUT
pin), its value is internally monitored and, as
Figure 7
) through a decoupling
Table 19
), the TMON I²C bit is
LNBH25