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CGS410 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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CGS410 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
8 / 18 page 30 Circuit Operation (Continued) Serial Bit 2 Reference Select A logic low configures XTLIN and XTLOUT for crystal mode A logic high configures for EX- TREF On power-up this bit is low (crystal mode) Serial Bits 3 4 Loop Filter Select LSB is loaded first Bit values are mapped by the following Bit 4 Bit 3 0 O External Mode 0 1 500 kHz Reference 1 0 15 MHz Reference 1 1 5 MHz Reference External mode selected on power-up Serial Bit 5 Load Clock (LCLK) Disable A logic low enables LCLK A logic high freezes the LCLK output low and disables the L counter Note that this is different from the effects of the L clock enable pin which is a synchronous disable and which only disables the output (leaving the counter operational) LCLK is enabled on power-up Serial Bit 6 PCLK Disable A logic low enables CMOS PCLK output A logic high freezes CMOS PCLK low CMOS PCLK is en- abled on power-up Serial Bit 7 Differential (DIFF) Out Disable A logic low enables Differen- tial Output A logic high causes both differential outputs to be driven below 400 mV DlFF out is enabled on power-up Serial Bit 8 Charge Pump Output (CPO) Select A logic low forces a 25 mA current pump A logic high forces a 75 mA current pump There is a 25 mA current pump on power-up Serial Bit 9 Charge Pump Output (CPO) Polarity A logic low forces a ‘‘normal’’ output response ie the charge pump sinks cur- rent when the feedback signal (N counter output) leads the reference signal (R counter output) A logic high forces an inverted response CPO polarity is in normal mode on power-up Serial Bit 10 Charge Pump (CPO) Disable A logic low enables charge pump activity A logic high Tri-States CPO activity CPO is enabled on power-up Serial Bit 11 Voltage Controlled Oscillator (VCO) Disable A logic low en- ables VCO operation A logic high disables VCO activity VCO is enabled on power-up Serial Bit 12 External VCO Enable (XVCO EN) A logic high enables the external VCO path This bit is disabled on power-up Serial Bit 13 Voltage Control Oscillator (VCO) Reset A logic high resets the VCO This means that the charge pump output is clamped to AGND to guarantee that the loop filter is dis- charged VCO reset is high (enabled) on power-up A logic low places the VCO in normal operating mode In order for the PLL to lock this bit must be returned low after power-up Serial Bits 14 15 Internal clock MUX SEL LSB (bit 14) is loaded first This MUX selects which clock signal is passed to the clock out- puts Bit values are mapped by the following Bit 15 Bit 14 0 0 XTAL2 Mode 0 1 P Counter Mode 1 0 External Clock Mode (Passthru) 1 1 Not Used The XTAL2 mode is selected on power-up Serial Bits 16 – 19 P counter modulus select LSB bit 16 is loaded first The P modulus range is 1 – 16 continuous Serial bits 16 – 19 are loaded with the desired modulus value b 1 (ie 0 – 15) P counter divides by modulus 4 on power-up Serial Bits 20 – 23 L counter modulus select LSB bit 20 is loaded first The L modulus range is 1 – 16 continuous Serial bits 20 – 23 are loaded with the desired modulus value b 1 (ie 0 – 15) L counter divides by modulus 4 on power-up Serial Bits 24 – 33 R counter modulus LSB (bit 24) is loaded first The R coun- ter divides continuously by the binary value loaded Modulus range is 1 – 1023 inclusive R is initialized at 20 on power-up Loading R e 0 is undefined Serial Bits 34 – 47 N counter modulus LSB (bit 34) is loaded first The N coun- ter divides by the binary value loaded Modulus range is 2 – 16383 inclusive N is initialized at 120 on power-up Load- ing N e 0orN e 1 is undefined 353 Power-Up Conditions At power-up the control register bits are set to provide initial operating conditions as follows 1 All clock outputs are active 2 The differential PCLK and CMOS PCLK outputs func- tion at a rate of XTAL2 The LCLK functions at a rate of XTAL8 3 The status of the internal register reflects the following N e 120 R e 20 P e 4 (bits 16 – 19 e 3) L e 4 (bits 20 – 23 e 3) 4 All other programmable bits are low except VCO RPST which is set high 8 |
Similar Part No. - CGS410 |
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Similar Description - CGS410 |
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