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TDA7427AAD Datasheet(PDF) 6 Page - STMicroelectronics |
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TDA7427AAD Datasheet(HTML) 6 Page - STMicroelectronics |
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6 / 21 page  GENERAL DESCRIPTION This circuit contains a frequency synthesiser and a loop filter for use in FM/AM radio tuning sys- tems. Only a VCO is required to build a complete PLL system. For auto search/stop operation an IF counter system is available. For FM and SW AM application, the counter works in a two-stage configuration. The first stage is a swallow counter with a two modulus (:32/33) precounter. The second stage is an 11-bit pro- grammable counter. For LW and MW application, a 16-bit programma- ble counter is available. The circuit receives the scaling factors for the pro- grammable counters and the values of the refer- ence frequencies via a I 2C bus interface. The reference frequency is generated by an inter- nal XTAL oscillator followed by the reference di- vider. The device can operate with XTAL oscilla- tor between 4 and 13MHz either in master mode and in slave mode. The reference and step frequencies are free se- lectable. (XTAL frequency divided by an integer value). The outputs signals of the phase detector are switching the programmable current sources. The loop filter integrates their currents to a DC voltage. Values of the current sources are programmable by 6 bits also received via the I 2C bus. To minimize the noise induced by the digital part of the system, a separate power supply supplies the internal loop filter amplifier. The loop gain can be set for different conditions by setting the cur- rent values of the charge/pump generator. IF COUNTER SYSTEM Two separate inputs are available for AM and FM IF signals. The level of integration is adjustable by six different measuring cycle times. The tolerance of the accepted count value is ad- justable, to reach an optimum compromise for search speed and precision of the evaluation. For the FM range the center frequency of the measured count value is adjustable in 32 steps, to get the possibility of fitting the IF filter toler- ance. In the AM range an IF frequency of 448 to 479KHz ( 10.684 to 10.715MHz for AM up-con- version) with 1KHz steps is available. PLL FREQUENCY SYNTHESIZER Input Amplifiers The signals applied on AM and FM inputs are am- plified to get a logic level in order to drive the fre- quency dividers. The typical input impedance for FM and AM in- puts is 4k Ω. MSB LSB FUNCTION SUBAD BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 PLL CHARGE PUMP 00H LPIN1/2 CURRH B1 B0 A3 A2 A1 A0 PLL COUNTER 01H PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0 PLL COUNTER 02H PC15 PC14 PC13 PC12 PC11 PC10 PC9 PC8 PLL REF COUNTER 03H RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0 PLL REF COUNTER 04H RC15 RC14 RC13 RC12 RC11 RC10 RC9 RC8 PLL LOCK DETECT 05H LDENA INLOCK D3 D2 D1 D0 PM1 PM0 IFC REF COUNTER 06H IRC7 IRC6 IRC5 IRC4 IRC3 IRC2 IRC1 IRC0 IFC REF COUNTER 07H IFCM1 IFCM0 IRC13 IRC12 IRC11 IRC10 IRC9 IRC8 IFC CONTROL 08H IFENA - - - - EW2 EW1 EW0 IFC CONTROL 09H IFS2 IFS1 IFS0 CF4 CF3 CF2 CF1 CF0 OSC ADJUST 0AH - - - OSC4 OSC3 OSC2 OSC1 OSC0 PORT EXTENSION 0BH - - DOUT3 DOUT4 DOUT5 DOUT6 DOUT2 DOUT1 Table 1. Address Organization TDA7427A 6/21 |
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