Datasheet LTC6990 (Analog Devices) - 8

LTC6990
PIN FUNCTIONS (DCB/S6) V+ (Pin 1/Pin 5):
Supply Voltage (2.25V to 5.5V). This Limit the capacitance on the SET pin to less than 10pF supply must be kept free from noise and ripple. It should to minimize jitter and ensure stability. Capacitance less be bypassed directly to the GND pin with a 0.1µF capacitor. than 100pF maintains the stability of the feedback circuit
DIV (Pin 2/Pin 4):
Programmable Divider and Hi-Z Mode regulating the VSET voltage. Input. A V+ referenced A/D converter monitors the DIV V+ pin voltage (VDIV) to determine a 4-bit result (DIVCODE). V OE OUT DIV may be generated by a resistor divider between V+ and GND. Use 1% resistors to ensure an accurate result. LTC6990 V+ The DIV pin and resistors should be shielded from the GND V+ C1 OUT pin or any other traces that have fast edges. Limit 0.1µF R1 the capacitance on the DIV pin to less than 100pF so that SET DIV V 6990 PF R DIV settles quickly. The MSB of DIVCODE (Hi-Z) deter- SET R2 mines the behavior of the output when OE is driven low. If Hi-Z = 0 the output is pulled low when disabled. If Hi-Z = 1 the output is placed in a high impedance condition
OE (Pin 4/Pin 1):
Output Enable. Drive high to enable the when disabled. output driver (Pin 6). Driving OE low disables the output asynchronously, so that the output is immediately forced
SET (Pin 3/Pin 3):
Frequency-Setting Input. The voltage low (Hi-Z = 0) or floated (Hi-Z = 1). When enabled, the on the SET pin (VSET) is regulated to 1V above GND. The output may temporarily remain low to synchronize with amount of current sourced from the SET pin (ISET) pro- the internal oscillator in order to eliminate pulse slivers. grams the master oscillator frequency. The ISET current range is 1.25µA to 40µA. The output oscillation will stop
GND (Pin 5/Pin 2):
Ground. Tie to a low inductance ground if I plane for best performance. SET drops below approximately 500nA. A resistor con- nected between SET and GND is the most accurate way to
OUT (Pin 6/Pin 6):
Oscillator Output. The OUT pin swings set the frequency. For best performance, use a precision from GND to V+ with an output resistance of approximately metal or thin film resistor of 0.5% or better tolerance and 30Ω. When driving an LED or other low-impedance load 50ppm/°C or better temperature coefficient. For lower ac- a series output resistor should be used to limit source/ curacy applications an inexpensive 1% thick film resistor sink current to 20mA. may be used. 6990fc 8 For more information www.linear.com/LTC6990 Document Outline Features Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Related Parts