TEF6721HL_4 © Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet Rev. 04 — 20 December 2005 10 of 48
Philips Semiconductors
TEF6721HL
Car radio tuner front-end for digital IF
minimum JFET drain source voltage is controlled by a Direct Current (DC) feedback loop
(pin VAMCASFB) in order to limit the cascode AGC range to 10 dB. If the cascode AGC is
not required, a simple RF AGC loop is possible by using only a PIN diode. In some
conditions, noise behavior will increase. In this case pins VAMCAS and VAMCASFB have
to be left open-circuit. In FM mode, the cascode switches off the JFET bias current to
reduce the total power consumption.
The AGC detection points for AM RF AGC are at the AM mixer input (threshold
programmable via the I
2
C-bus) and the AM and FM IF AGC amplifier input (fixed
threshold).
In FM mode the AM AGC can be activated via the I
2
C-bus to sink a constant current of
1 mA from the PIN diode.
7.10 FM/AM RF AGC buffer
This output current can be used to reduce the gain of active antennas before start of
RF AGC.
The output (open-collector) sinks a current which in AM mode is proportional to the
voltage at pin TRFAMAGC and in FM mode proportional to the RF level detector voltage
(pin TFMAGC) inside the FM AGC.
8. I
2
C-bus protocol
8.1 I
2
C-bus specification
SDA and SCL HIGH and LOW levels are specified according to a 3.3 V I
2
C-bus. The bus
pins tolerate also thresholds of a 5 V bus.
The standard I
2
C-bus specification is expanded by the following definitions.
IC addresses:
• 1st IC address C2h: 1100001 R/W
• 2nd IC address C0h: 1100000 R/W
• 3rd IC address C4h: 1100010 R/W.
Structure of the I
2
C-bus logic: slave transceiver with auto increment.
Subaddresses are not used.
The second I
2
C-bus address can be selected by connecting pin ADDRSEL via a 120 kΩ
resistor to ground. The third I
2
C-bus address can be selected by connecting
pin ADDRSEL via a 33 kΩ resistor to ground.
The maximum bit rate for this device is 100 kbit/s.
The I
2
C-bus interface is extended with an enable input (pin BUSENABLE). If pin
BUSENABLE is HIGH the communication with the device is active; if pin BUSENABLE is
LOW the signals on the I
2
C-bus are ignored so that higher bit rates (> 100 kbit/s) can be
used to communicate with other devices on the same I
2
C-bus. The enable signal must not
change while bus communication takes place.
