LTC6990CS6-TRPBF 查看數據表（PDF） - Linear Technology

零件编号

产品描述 (功能)

生产厂家

LTC6990CS6-TRPBF

TimerBlox: Voltage Controlled Silicon Oscillator

Linear Technology 

LTC6990

OPERATION

Changing DIVCODE After Start-Up

Following start-up, the A/D converter will continue

monitoring VDIV for changes. Changes to DIVCODE will

be recognized slowly, as the LTC6990 places a priority on

eliminating any “wandering” in the DIVCODE. The typical

delay depends on the difference between the old and

new DIVCODE settings and is proportional to the master

oscillator period.

tDIVCODE = 16 • (∆DIVCODE + 6) • tMASTER

A change in DIVCODE will not be recognized until it is

stable, and will not pass through intermediate codes. A

digital filter is used to guarantee the DIVCODE has settled

to a new value before making changes to the output. Then

the output will make a clean (glitchless) transition to the

new divider setting.

Start-Up Time

When power is first applied to the LTC6990 the power-on

reset (POR) circuit will initiate the start-up time, tSTART.

The OUT pin is floated (high-impedance) during this time.

The typical value for tSTART ranges from 0.5ms to 8ms

depending on the master oscillator frequency (indepen-

dent of NDIV):

tSTART(TYP) = 500 • tMASTER

The start-up time may be longer if the supply or DIV

pin voltages are not stable. For this reason, it is recom-

mended to minimize the capacitance on the DIV pin so it

will properly track V+.

DIV

1V/DIV

576µs

OUT

1V/DIV

V+ = 3.3V

RSET = 200k

100µs/DIV

6990 F05

Figure 5. DIVCODE Change from 5 to 2

V+

1V/DIV

OUT

1V/DIV

470µs

OUTPUT CONNECTED

TO 1.25V THROUGH 25k

TO SHOW Hi-Z

V+ = 2.5V

DIVCODE = 4

RSET = 50k

100µs/DIV

Figure 6. Typical Start-Up

6990 F06

For more information www.linear.com/LTC6990

6990fc

13

Share Link: