Fout = –1.4kHz per microampere of photo diode current, IPD. The LTC6990 is a precision silicon oscillator with a programmable frequency range of 488Hz to 2MHz. It can be used as a fixed-frequency or voltage-controlled oscillator (VCO). The LTC6990 is part of the TimerBlox family of versatile silicon timing devices. A single resistor, RSET, programs the LTC6990’s internal master oscillator frequency. The output frequency is determined by this master oscillator and an 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 and 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 enable function that is synchronized with the master oscillator to ensure clean, glitch-free output pulses. The disabled output can be configured to be high impedance or forced low.