LTC6906

5

6906fc

PIN FUNCTIONS

OUT (Pin 1): Oscillator Output. The OUT pin swings from

150Ω. For micropower operation, the load resistance must

be kept as high as possible and the load capacitance as

low as possible.

GND (Pin 2): Ground.

DIV (Pin 3): Divider Setting Input. This three-level input

selects one of three internal digital divider settings, de-

termining the value of N in the frequency equation. Tie to

When left floating, the LTC6906 pulls Pin 3 to mid-supply

with a 2.5M resistor. When Pin 3 is floating, care should

be taken to reduce coupling from the OUT pin and its

trace to Pin 3. Coupling can be reduced by increasing the

physical space between traces or by shielding the DIV pin

with grounded metal.

SET (Pin 4): Frequency Setting Resistor Input. Connect

frequency. For best performance use a precision metal- or

thin-film resistor of 0.5% or better tolerance and 50ppm/°C

or better temperature coefficient. For lower accuracy ap-

plications, an inexpensive 1% thick-film resistor may be

than 10pF to reduce jitter and to ensure stability. Capaci-

tance greater than 10pF could cause the LTC6906 internal

feedback circuits to oscillate. The voltage on the SET pin

is approximately 650mV and decreases with temperature

by about –2.2mV/°C.

GRD (Pin 5): Guard Signal. This pin can be used to reduce

PC board leakage across the frequency setting resistor,

SET pin and shunts leakage current away from the SET pin.

To control leakage, connect a bare copper trace (a trace

with no solder mask) to GRD and loop it around the SET

pin and all PC board metal connected to SET.

Voltage Supply (2.25V to 3.6V). This supply

is internally decoupled with a 20Ω resistor in series with

an 800pF capacitor. No external decoupling capacitor is

kept reasonably free of noise and ripple.

BLOCK DIAGRAM

4

6

1

OP AMP

150Ω DRIVER

OUT

6906 BD

3

DIV

PROGRAMMABLE

DIVIDER (n)

(1, 3, 10)

THREE-LEVEL

INPUT

DETECTOR

VOLTAGE

CONTROLLED

OSCILLATOR

(MASTER OSCILLATOR)

SET

SET

2

GND

20

800pF

FREQUENCY-TO-CURRENT

CONVERTERS

DECOUPLING

NETWORK

BUFFER

GRD

5M

5M

DIVIDER

SELECT

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