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1. Describe
The LTC®6990 is a precision silicon oscillator with a programmable frequency range from 488Hz to 2MHz. Can be used as a fixed frequency or voltage controlled oscillator (Voltage Controlled Oscillator). The LTC6990 is part of the TimerBlox® family of multifunction silicon timer devices. A single resistor, RSET, programs the LTC6990's internal primary oscillator frequency. The output frequency is determined by this main oscillator and the internal frequency divider NDIV, programmable to eight settings from 1 to 128. Optionally, a second resistor at the SET input provides linear voltage control of the output frequency, which can be used for frequency modulation. A narrow or wide VCO tuning range can be configured by the appropriate selection of the two resistors. The LTC6990 includes an A-device synchronization Enable function to ensure clean, glitch-free output pulses. Disabled outputs can be configured as high impedance or forced low impedance. For easy configuration of the LTC6990, use the TimerBlox LTC6990: Web-Based Voltage Controlled Oscillator Design Tools.
2. Feature
1. Fixed frequency or voltage control operation
- Correction: Single-resistor programming frequency, maximum error <1.5%
- VCO: Two resistors set the VCO center frequency and tuning range
2. Frequency range: 488Hz to 2MHz
3. 2.25V to 5.5V single supply 72µA Supply Current at 100kHz
4. 500µs startup time
5. VCO bandwidth >300kHz at 1MHz
6. CMOS logic output source/sink 20mA
7. 50% duty cycle square wave output
8. Output enable (select low impedance or high impedance when disabled)
9. 55°C to 125°C operating temperature range
10. Available in low profile (1mm) SOT-23 (ThinSOT™) and 2mm × 3mm DFN packages
11. AEC-Q100 qualified for automotive applications
3. Application
1. Low-cost precision programmable oscillator
2. Voltage Controlled Oscillator
3. High vibration, high acceleration environment
4. Alternatives to fixed crystal and ceramic oscillators
5. Portable and battery powered devices
4. Pin configuration
5. Pin Description
1. V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V).
2. DIV (Pin 2/Pin 4): Programmable Divider and Hi-Z Mode Input.
3. SET (Pin 3/Pin 3): Frequency-Setting Input.
4. OE (Pin 4/Pin 1): Output Enable.
5. GND (Pin 5/Pin 2): Ground.
6. OUT (Pin 6/Pin 6): Oscillator Output.
6. Application Information
Furthermore, by judiciously choosing the VCO's specification, the frequency error (percentage) change due to VSET is reduced to ΔVSET/VSET = ±3%. To achieve this improvement, the design must obey three conditions. First, the VIN voltage must always be in the positive range. Second, choose VMAX/VMIN≥fMAX/fMIN. Finally, select RVCO/RSET ≥ R4/R3.
