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LMX1600SLB Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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LMX1600SLB Datasheet(HTML) 9 Page - National Semiconductor (TI) |
9 / 14 page 2.0 Programming Description (Continued) 1.1 GHz option (12 bit) MAIN_B_CNTR Divide Ratio 11 10 9876543210 3 000000000011 4 000000000100 • •••••••••••• 4,095 111111111111 Note 14: Divide ratio: 3 to 4,095 (Divide ratios less than 3 are prohibited) MAIN_B_CNTR ≥ MAIN_A_CNTR. See section 2.3.7 for calculation of VCO output frequency. 2.3.7 Pulse Swallow Function The N divider counts such that it divides the VCO RF frequency by (P+1) for A times, and then divides by P for (B – A ) times. The B value (B_CNTR) must be ≥ 3. The continuous divider range for the Main PLL N divider is from 992 to 65,535 for 2 GHz option, from 240 to 65,535 for 1.1 GHz option, and from 56 to 32,767 for 500 MHz option. Divider ratios less than the minimum value are achievable as long as the binary counter value is greater than or equal to the swallow counter value (B_CNTR ≥ A_CNTR). f VCO =Nx(fOSC /R) N=(P x B) + A f VCO: Output frequency of external voltage controlled oscillator (VCO) f OSC: Output frequency of the external reference frequency oscillator (input to OSC IN). R: Preset divide ratio of binary programmable reference counter (R_CNTR) N: Preset divide ratio of main programmable integer N counter (N_CNTR) B: Preset divide ratio of binary programmable B counter (B_CNTR) A: Preset value of binary 4-bit swallow A counter (A _CNTR) P: Preset modulus of dual modulus prescaler (P = 32 for 2 GHz option, P=16 for 1.1 GHz option, and P=8 for 500 MHz option) 2.4 CHARGE PUMP CONTROL WORD (CP_WORD) MSB LSB AUX_CP_GAIN MAIN_CP_GAIN AUX_PD_POL MAIN_PD_POL BIT LOCATION FUNCTION 0 1 AUX_CP_GAIN MAIN_R[17] Aux Charge Pump Current Gain LOW HIGH MAIN_CP_GAIN MAIN_R[16] Main Charge Pump Current Gain LOW HIGH AUX_PD_POL MAIN_R[15] Aux Phase Detector Polarity Negative Positive MAIN_PD_POL MAIN_R[14] Main Phase Detector Polarity Negative Positive AUX_CP_GAIN (MAIN_R[17]) and MAIN_CP_GAIN (MAIN_R[16]) are used to select charge pump current magnitude either low gain mode (160 µA typ) or high gain mode (1600 µA typ) AUX_ PD_POL (MAIN_R[15]) and MAIN_ PD_POL (MAIN_R[14]) are respectively set to one when Aux or Main VCO character- istics are positive as in (1) below. When VCO frequency decreases with increasing control voltage (2) PD_POL should set to zero. 9 www.national.com |
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