LTC6990IDCB-TRMPBF データシートの表示（PDF） - Analog Devices

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LTC6990IDCB-TRMPBF

TimerBlox: Voltage Controlled Silicon Oscillator

Analog Devices 

LTC6990

OPERATION

Table 1. DIVCODE Programming

DIVCODE

Hi-Z

NDIV

0

0

1

1

0

2

2

0

4

3

0

8

4

0

16

5

0

32

6

0

64

7

0

128

8

1

128

9

1

64

10

1

32

11

1

16

12

1

8

13

1

4

14

1

2

15

1

1

Recommended fOUT

62.5kHz to 1MHz

31.25kHz to 500kHz

15.63kHz to 250kHz

7.813kHz to 125kHz

3.906kHz to 62.5kHz

1.953kHz to 31.25kHz

976.6Hz to 15.63kHz

488.3Hz to 7.813kHz

488.3Hz to 7.813kHz

976.6Hz to 15.63kHz

1.953kHz to 31.25kHz

3.906kHz to 62.5kHz

7.813kHz to 125kHz

15.63kHz to 250kHz

31.25kHz to 500kHz

62.5kHz to 1MHz

R1 (k)

Open

976

976

1000

1000

1000

1000

1000

887

681

523

392

280

182

102

Short

R2 (k)

Short

102

182

280

392

523

681

887

1000

1000

1000

1000

1000

976

976

Open

VDIV/V+

≤ 0.03125 ±0.015

0.09375 ±0.015

0.15625 ±0.015

0.21875 ±0.015

0.28125 ±0.015

0.34375 ±0.015

0.40625 ±0.015

0.46875 ±0.015

0.53125 ±0.015

0.59375 ±0.015

0.65625 ±0.015

0.71875 ±0.015

0.78125 ±0.015

0.84375 ±0.015

0.90625 ±0.015

≥ 0.96875 ±0.015

Table 1 offers recommended 1% resistor values that accu-

rately produce the correct voltage division as well as the

corresponding NDIV and Hi-Z values for the recommended

resistor pairs. Other values may be used as long as:

1. The VDIV/V+ ratio is accurate to ±1.5% (including resis-

tor tolerances and temperature effects)

2. The driving impedance (R1||R2) does not exceed 500kΩ.

If the voltage is generated by other means (i.e. the output

of a DAC) it must track the V+ supply voltage. The last

column in Table 1 shows the ideal ratio of VDIV to the

supply voltage, which can also be calculated as:

VDIV

V+

=

DIVCODE + 0.5

16

± 1.5%

For example, if the supply is 3.3V and the desired DIVCODE

is 4, VDIV = 0.281 • 3.3V = 928mV ± 50mV.

Figure 2 illustrates the information in Table 1, showing

that NDIV is symmetric around the DIVCODE midpoint.

On start-up, the DIV pin A/D converter must determine

the correct DIVCODE before the output is enabled. If VDIV

1000

Hi-Z BIT = 0

Hi-Z BIT = 1

0

1

100

2

15

14

13

3

4

10

5

12

11

10

6

9

78

1

0.1

0V

0.5• V+

INCREASING VDIV

RECOMMENDED RANGE

EXTENDED RANGE

V+

6990 F02

Figure 2. Frequency Range and Hi-Z Bit vs DIVCODE

For more information www.analog.com

Rev. D

11

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