U4254BM-M Datasheet, PDF (7/14 Pages) ATMEL Corporation – Low-noise AM/FM Antenna Impedance Matching IC

U4254BM-M
Functional Description
The U4254BM-M is an integrated AM/FM antenna impedance matching circuit. It com-
pensates cable losses between the antenna (for example windshield, roof or bumper
antennas) and the car radio which is usually placed far away from the antenna.
The FM amplifier provides excellent noise performance. External components are used
to adjust the gain and the input-output matching impedance. Therefore, it is possible to
adjust the amplifier to various cable impedances (usually 50, 75 or 150 Ω). To protect
the amplifier against input overload, an Automatic Gain Control (AGC) is included on the
chip. The AGC observes the AC voltage at the FM amplifier output, rectifies this signal,
and delivers DC current to dampen the input antenna signal via an external PIN diode.
The threshold for the AGC is adjustable. Simple and temperature-compensated biasing
is possible due to the integrated voltage reference V_Ref2.
The AM part consists of a buffer amplifier. The voltage gain of this stage is approxi-
mately one. The input resistance is 470 kΩ, the input capacitance less than 10 pF. The
output resistance is 125 Ω. An excellent dynamic range is achieved due to the comple-
mentary CMOS source follower stage.
Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Reference point is ground (pins 2 and 7)
Parameters
Symbol
Value
Unit
Supply voltage
V_S
8.8
V
Power dissipation, P_tot at T_amb = 85° C
P_tot
460
mW
Junction temperature
T_j
150
°C
Ambient temperature
T_amb
-40 to +85
°C
Storage temperature
T_stg
-50 to +150
°C
Electrostatic handling (HBM at ESD S.5.1)
±V_ESD
±1000
V
Thermal Resistance
Parameters
Junction ambient
Symbol
R_thJA
Value
140
Unit
K/W
7
4772B–AUDR–11/03