Zlnb254 – Diodes ZLNB254 User Manual
Page 2
ZLNB254
ZLNB254
Document number: Ds32002 Rev. 1
2 of 8
October 2009
© Diodes Incorporated
DESCRIPTION
The ZLNB254 is a dual DiSEqC™ tone detector IC for
multiple output LNBs, satellite distribution systems,
set-top boxes and DiSEqC™ peripherals. Although
intended for use with 22kHz DiSEqC™ signals, the
ZLNB254 can be used over the frequency range of
10kHz to 60kHz so it can detect standard 22kHz
satellite band control signals as well as regional
variations such as those in Japan.
The minimum of external components are required to
enable this two-channel tone filter and fast envelope
detector. The ZLNB254 is particularly suited to low
signal level, high distortion DiSEqC™ signal detecting
applications.
The ZLNB254 includes circuitry necessary to detect
the presence of a 22kHz tones modulated on the
supply inputs to a LNB or switchbox. The TD outputs
are set low on detection of a valid tone or DiSEqC™
signal when applied to the FIN inputs.
To enable system flexibility user control is given over
the gain and the lower frequency limit of the filter by
using a single external resistor and capacitor per
channel. The higher frequency limit of the filters is set
internally above 60kHz. The remaining detector
circuits utilises no other external components.
The tone detector can be used to sense either
continuous tones or coded tone bursts such as used
in DiSEqC™ and similar control systems. To ensure
system reliability the tone detector rejects unwanted
signals including transients from other parts of the
LNB system without the use of any external
components.
The TD outputs are designed to be compatible with
LSTTL and CMOS loads so can drive a
microcontroller or other logic directly.
To give further protection the resistor which is used to
set the filter gain also provides ESD protection.
The ZNBL254 provides a small simple solution and is
packaged in the TDFN2020-6 surface mount
package.
Pinout Diagram
TDFN2020-6 Top view
3
2
1
4
6
FIN1
GND
TD2
FIN2
TD1
5
VCC