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ML2731CT Arkusz danych(PDF) 7 Page - Micro Linear Corporation |
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ML2731CT Arkusz danych(HTML) 7 Page - Micro Linear Corporation |
7 / 12 page ML2731 7 January, 2000 PRELIMINARY DATASHEET PRELIMINARY CRYSTAL OSCILLATOR The crystal oscillator circuit is powered by an on chip regulator and generates a square wave signal and a sine wave signal. The sine wave is intended for radio PLL circuits, and the square wave clock for the digital circuits. The frequency range of operation is 10 to 40MHz (determined by the external crystal). The crystal oscillator can also be overdriven by connecting an external oscillator to pin 15 (XIN). The crystal oscillator square wave and sine wave signal outputs are enabled in STANDBY, PRETX and TRANSMIT modes. (See Figures 2 and 3) The oscillator circuit is enabled by the PDN logic control pin and turns on and generates stable output signals within 20mS of being enabled. Figure 2: Typical 32 MHz Square wave output signal (1k W+10pF load, VCC = 3.3V) Figure 3: Typical 32 MHz sine wave output signal (1k W+0pF load, and 1k W+10pF load, VCC = 3.3V) NEGATIVE VOLTAGE GENERATOR When driven by a 32 MHz crystal, the charge pump of the ML2731 is clocked with a 2.66 MHz signal. Because the clock frequency is so high, the negative voltage generator requires only small ceramic capacitors on C1 and C2 for operation. (Figure 4) Typically they have values of 100nF. The quick response time (Figure 5), due in part to the small circuit capacitance, allows the charge pump to be disabled when not needed thus reducing power consumption. Figure 5: Typical negative voltage generator on and off timing (using 100nF capacitors on pins C1 and C2) FUNCTIONAL DESCRIPTION 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 –0.5 TIME (ns) 010 30 50 40 20 TIME (ns) 0 60 40 80 20 1.9 1.8 1.7 1.6 1.5 1.4 10 70 50 30 Cap: 10pF none Figure 4: Typical C1 and C2 Noise Shunt Configuration NEGEN (pin 7) enables the negative voltage generator during the PRETX and TRANSMIT modes of operation. Output from the negative voltage generator is used internally by the ML2731 to supply the op amp in the PA current control circuit. The resulting voltage is applied to VBIAS for controlling an external PA. The negative voltage generator enables the ML2731 to provide a typical bias voltage in the range of –2.9 V to 0V. 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 TIME (ms) 00.8 0.6 0.4 0.2 0.1 0.7 0.5 0.3 0.5 0.0 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 VNEG BIAS VNEG C1 C2 12 11 10 100nF 100nF 100nF Figure 6: Negative voltage output ripple ( mV) (using 100nF bypass and reservoir capacitance) 600 500 400 300 200 100 0 FREQUENCY (MHz) 04 6 10 8 2 |
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