e01ch36.PDF

(40 KB) Pobierz

036

Electronically Trimmable Capacitor

+2V7...+5V5

R i

12p

100n

u

i

IC1

2

CP

Example: 5 pulses = 7p54

9p3...9p6

CP

4

CP

1

DAT

CM

35p

CM

6p4...13p3

3

6

EN

single ended

CM

014135 - 13

Q enhancement circuit

5

MAX1474

014135 - 12

014135 - 11

R i

CM

R

e

Maxim ( www.maxim-ic.com ) have recently introduced an

innovative IC the MAX1474 also called a FLECAP (Fine

Line Electronically trimmable Capacitor). This device is

basically a capacitor that can be electronically adjusted

through the range of 6.4 pF to 13.3 pF in steps of 0.22 pF

and is supplied as a tiny SC70 outline package. Capacitor

adjustment is performed by sending a series of pulses to

the DAT input while holding the EN input high. The num-

ber of pulses (up to a maximum of 31) are counted and

latched into an in internal register on the falling edge of the

EN input. At power-up with no pulses sent, the capacitance

would be 6.4 pF in a single-ended application or 0.42 pF in

a differential application.

DC voltage at the variable capacitance pins must be

within the chip supply voltage and the signal swing can be

up to 300 mV either side of V DD and V SS . For optimum per-

formance it is recommended to connect the CM capacitor

pin to the lowest impedance node in your application

(ground or supply if possible).

CP

u

u e

i

0p4...10p9

differential

014135 - 14

An internal multiplexer introduces a series resistance

with the trimmable capacitor elements and this leads to a

relatively poor quality (Q) factor of the capacitor. The dia-

gram shows a method of enhancing the Q factor with fixed

capacitors this will however reduce the range of the FLE-

CAP.

One major application for this device will be to replace

the variable trimmers usually necessary in quartz oscilla-

tor circuits. To increase capacitance range several FLE-

CAP’s can of course be connected in parallel or series.

(014135-1)

12/2001

Elektor Electronics

73

855738834.038.png

855738834.039.png

855738834.040.png

855738834.041.png

855738834.001.png

855738834.002.png

855738834.003.png

855738834.004.png

855738834.005.png

855738834.006.png

855738834.007.png

855738834.008.png

855738834.009.png

855738834.010.png

855738834.011.png

855738834.012.png

855738834.013.png

855738834.014.png

855738834.015.png

855738834.016.png

855738834.017.png

855738834.018.png

855738834.019.png

855738834.020.png

855738834.021.png

855738834.022.png

855738834.023.png

855738834.024.png

855738834.025.png

855738834.026.png

855738834.027.png

855738834.028.png

855738834.029.png

855738834.030.png

855738834.031.png

855738834.032.png

855738834.033.png

855738834.034.png

855738834.035.png

855738834.036.png

855738834.037.png

Plik z chomika:

Inne pliki z tego folderu:

bge.jpg (26 KB)
detail11.htm (6 KB)
detail1.htm (5 KB)
detail10.htm (4 KB)
e011016.PDF (1901 KB)

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin